2505 lines
74 KiB
C
2505 lines
74 KiB
C
/*
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* Read-Copy Update mechanism for mutual exclusion (tree-based version)
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* Internal non-public definitions that provide either classic
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* or preemptible semantics.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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*
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* Copyright Red Hat, 2009
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* Copyright IBM Corporation, 2009
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*
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* Author: Ingo Molnar <mingo@elte.hu>
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* Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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*/
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#include <linux/delay.h>
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#include <linux/gfp.h>
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#include <linux/oom.h>
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#include <linux/smpboot.h>
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#define RCU_KTHREAD_PRIO 1
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#ifdef CONFIG_RCU_BOOST
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#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
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#else
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#define RCU_BOOST_PRIO RCU_KTHREAD_PRIO
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#endif
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#ifdef CONFIG_RCU_NOCB_CPU
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static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
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static bool have_rcu_nocb_mask; /* Was rcu_nocb_mask allocated? */
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static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */
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static char __initdata nocb_buf[NR_CPUS * 5];
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#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
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/*
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* Check the RCU kernel configuration parameters and print informative
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* messages about anything out of the ordinary. If you like #ifdef, you
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* will love this function.
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*/
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static void __init rcu_bootup_announce_oddness(void)
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{
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#ifdef CONFIG_RCU_TRACE
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printk(KERN_INFO "\tRCU debugfs-based tracing is enabled.\n");
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#endif
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#if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
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printk(KERN_INFO "\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
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CONFIG_RCU_FANOUT);
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#endif
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#ifdef CONFIG_RCU_FANOUT_EXACT
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printk(KERN_INFO "\tHierarchical RCU autobalancing is disabled.\n");
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#endif
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#ifdef CONFIG_RCU_FAST_NO_HZ
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printk(KERN_INFO
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"\tRCU dyntick-idle grace-period acceleration is enabled.\n");
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#endif
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#ifdef CONFIG_PROVE_RCU
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printk(KERN_INFO "\tRCU lockdep checking is enabled.\n");
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#endif
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#ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
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printk(KERN_INFO "\tRCU torture testing starts during boot.\n");
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#endif
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#if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
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printk(KERN_INFO "\tDump stacks of tasks blocking RCU-preempt GP.\n");
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#endif
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#if defined(CONFIG_RCU_CPU_STALL_INFO)
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printk(KERN_INFO "\tAdditional per-CPU info printed with stalls.\n");
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#endif
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#if NUM_RCU_LVL_4 != 0
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printk(KERN_INFO "\tFour-level hierarchy is enabled.\n");
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#endif
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if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF)
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printk(KERN_INFO "\tExperimental boot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
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if (nr_cpu_ids != NR_CPUS)
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printk(KERN_INFO "\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
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#ifdef CONFIG_RCU_NOCB_CPU
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if (have_rcu_nocb_mask) {
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if (cpumask_test_cpu(0, rcu_nocb_mask)) {
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cpumask_clear_cpu(0, rcu_nocb_mask);
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pr_info("\tCPU 0: illegal no-CBs CPU (cleared).\n");
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}
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cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask);
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pr_info("\tExperimental no-CBs CPUs: %s.\n", nocb_buf);
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if (rcu_nocb_poll)
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pr_info("\tExperimental polled no-CBs CPUs.\n");
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}
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#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
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}
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#ifdef CONFIG_TREE_PREEMPT_RCU
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struct rcu_state rcu_preempt_state =
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RCU_STATE_INITIALIZER(rcu_preempt, call_rcu);
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DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data);
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static struct rcu_state *rcu_state = &rcu_preempt_state;
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static int rcu_preempted_readers_exp(struct rcu_node *rnp);
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/*
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* Tell them what RCU they are running.
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*/
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static void __init rcu_bootup_announce(void)
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{
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printk(KERN_INFO "Preemptible hierarchical RCU implementation.\n");
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rcu_bootup_announce_oddness();
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}
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/*
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* Return the number of RCU-preempt batches processed thus far
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* for debug and statistics.
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*/
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long rcu_batches_completed_preempt(void)
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{
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return rcu_preempt_state.completed;
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}
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EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt);
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/*
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* Return the number of RCU batches processed thus far for debug & stats.
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*/
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long rcu_batches_completed(void)
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{
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return rcu_batches_completed_preempt();
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}
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EXPORT_SYMBOL_GPL(rcu_batches_completed);
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/*
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* Force a quiescent state for preemptible RCU.
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*/
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void rcu_force_quiescent_state(void)
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{
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force_quiescent_state(&rcu_preempt_state);
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}
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EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
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/*
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* Record a preemptible-RCU quiescent state for the specified CPU. Note
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* that this just means that the task currently running on the CPU is
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* not in a quiescent state. There might be any number of tasks blocked
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* while in an RCU read-side critical section.
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*
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* Unlike the other rcu_*_qs() functions, callers to this function
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* must disable irqs in order to protect the assignment to
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* ->rcu_read_unlock_special.
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*/
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static void rcu_preempt_qs(int cpu)
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{
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struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
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if (rdp->passed_quiesce == 0)
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trace_rcu_grace_period("rcu_preempt", rdp->gpnum, "cpuqs");
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rdp->passed_quiesce = 1;
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current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
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}
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/*
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* We have entered the scheduler, and the current task might soon be
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* context-switched away from. If this task is in an RCU read-side
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* critical section, we will no longer be able to rely on the CPU to
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* record that fact, so we enqueue the task on the blkd_tasks list.
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* The task will dequeue itself when it exits the outermost enclosing
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* RCU read-side critical section. Therefore, the current grace period
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* cannot be permitted to complete until the blkd_tasks list entries
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* predating the current grace period drain, in other words, until
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* rnp->gp_tasks becomes NULL.
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*
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* Caller must disable preemption.
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*/
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static void rcu_preempt_note_context_switch(int cpu)
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{
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struct task_struct *t = current;
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unsigned long flags;
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struct rcu_data *rdp;
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struct rcu_node *rnp;
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if (t->rcu_read_lock_nesting > 0 &&
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(t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
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/* Possibly blocking in an RCU read-side critical section. */
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rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
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rnp = rdp->mynode;
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raw_spin_lock_irqsave(&rnp->lock, flags);
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t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
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t->rcu_blocked_node = rnp;
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/*
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* If this CPU has already checked in, then this task
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* will hold up the next grace period rather than the
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* current grace period. Queue the task accordingly.
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* If the task is queued for the current grace period
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* (i.e., this CPU has not yet passed through a quiescent
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* state for the current grace period), then as long
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* as that task remains queued, the current grace period
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* cannot end. Note that there is some uncertainty as
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* to exactly when the current grace period started.
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* We take a conservative approach, which can result
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* in unnecessarily waiting on tasks that started very
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* slightly after the current grace period began. C'est
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* la vie!!!
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*
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* But first, note that the current CPU must still be
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* on line!
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*/
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WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0);
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WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
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if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) {
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list_add(&t->rcu_node_entry, rnp->gp_tasks->prev);
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rnp->gp_tasks = &t->rcu_node_entry;
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#ifdef CONFIG_RCU_BOOST
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if (rnp->boost_tasks != NULL)
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rnp->boost_tasks = rnp->gp_tasks;
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#endif /* #ifdef CONFIG_RCU_BOOST */
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} else {
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list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
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if (rnp->qsmask & rdp->grpmask)
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rnp->gp_tasks = &t->rcu_node_entry;
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}
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trace_rcu_preempt_task(rdp->rsp->name,
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t->pid,
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(rnp->qsmask & rdp->grpmask)
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? rnp->gpnum
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: rnp->gpnum + 1);
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raw_spin_unlock_irqrestore(&rnp->lock, flags);
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} else if (t->rcu_read_lock_nesting < 0 &&
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t->rcu_read_unlock_special) {
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/*
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* Complete exit from RCU read-side critical section on
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* behalf of preempted instance of __rcu_read_unlock().
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*/
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rcu_read_unlock_special(t);
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}
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/*
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* Either we were not in an RCU read-side critical section to
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* begin with, or we have now recorded that critical section
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* globally. Either way, we can now note a quiescent state
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* for this CPU. Again, if we were in an RCU read-side critical
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* section, and if that critical section was blocking the current
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* grace period, then the fact that the task has been enqueued
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* means that we continue to block the current grace period.
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*/
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local_irq_save(flags);
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rcu_preempt_qs(cpu);
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local_irq_restore(flags);
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}
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/*
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* Check for preempted RCU readers blocking the current grace period
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* for the specified rcu_node structure. If the caller needs a reliable
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* answer, it must hold the rcu_node's ->lock.
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*/
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static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
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{
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return rnp->gp_tasks != NULL;
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}
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/*
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* Record a quiescent state for all tasks that were previously queued
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* on the specified rcu_node structure and that were blocking the current
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* RCU grace period. The caller must hold the specified rnp->lock with
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* irqs disabled, and this lock is released upon return, but irqs remain
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* disabled.
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*/
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static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
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__releases(rnp->lock)
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{
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unsigned long mask;
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struct rcu_node *rnp_p;
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if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
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raw_spin_unlock_irqrestore(&rnp->lock, flags);
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return; /* Still need more quiescent states! */
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}
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rnp_p = rnp->parent;
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if (rnp_p == NULL) {
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/*
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* Either there is only one rcu_node in the tree,
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* or tasks were kicked up to root rcu_node due to
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* CPUs going offline.
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*/
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rcu_report_qs_rsp(&rcu_preempt_state, flags);
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return;
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}
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/* Report up the rest of the hierarchy. */
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mask = rnp->grpmask;
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raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
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raw_spin_lock(&rnp_p->lock); /* irqs already disabled. */
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rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags);
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}
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/*
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* Advance a ->blkd_tasks-list pointer to the next entry, instead
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* returning NULL if at the end of the list.
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*/
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static struct list_head *rcu_next_node_entry(struct task_struct *t,
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struct rcu_node *rnp)
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{
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struct list_head *np;
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np = t->rcu_node_entry.next;
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if (np == &rnp->blkd_tasks)
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np = NULL;
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return np;
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}
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/*
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* Handle special cases during rcu_read_unlock(), such as needing to
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* notify RCU core processing or task having blocked during the RCU
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* read-side critical section.
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*/
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void rcu_read_unlock_special(struct task_struct *t)
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{
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int empty;
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int empty_exp;
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int empty_exp_now;
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unsigned long flags;
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struct list_head *np;
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#ifdef CONFIG_RCU_BOOST
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struct rt_mutex *rbmp = NULL;
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#endif /* #ifdef CONFIG_RCU_BOOST */
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struct rcu_node *rnp;
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int special;
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/* NMI handlers cannot block and cannot safely manipulate state. */
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if (in_nmi())
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return;
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local_irq_save(flags);
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/*
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* If RCU core is waiting for this CPU to exit critical section,
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* let it know that we have done so.
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*/
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special = t->rcu_read_unlock_special;
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if (special & RCU_READ_UNLOCK_NEED_QS) {
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rcu_preempt_qs(smp_processor_id());
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}
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/* Hardware IRQ handlers cannot block. */
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if (in_irq() || in_serving_softirq()) {
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local_irq_restore(flags);
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return;
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}
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/* Clean up if blocked during RCU read-side critical section. */
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if (special & RCU_READ_UNLOCK_BLOCKED) {
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t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
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/*
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* Remove this task from the list it blocked on. The
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* task can migrate while we acquire the lock, but at
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* most one time. So at most two passes through loop.
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*/
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for (;;) {
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rnp = t->rcu_blocked_node;
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raw_spin_lock(&rnp->lock); /* irqs already disabled. */
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if (rnp == t->rcu_blocked_node)
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break;
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raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
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}
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empty = !rcu_preempt_blocked_readers_cgp(rnp);
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empty_exp = !rcu_preempted_readers_exp(rnp);
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smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
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np = rcu_next_node_entry(t, rnp);
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list_del_init(&t->rcu_node_entry);
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t->rcu_blocked_node = NULL;
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trace_rcu_unlock_preempted_task("rcu_preempt",
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rnp->gpnum, t->pid);
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if (&t->rcu_node_entry == rnp->gp_tasks)
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rnp->gp_tasks = np;
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if (&t->rcu_node_entry == rnp->exp_tasks)
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rnp->exp_tasks = np;
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#ifdef CONFIG_RCU_BOOST
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if (&t->rcu_node_entry == rnp->boost_tasks)
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rnp->boost_tasks = np;
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/* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */
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if (t->rcu_boost_mutex) {
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rbmp = t->rcu_boost_mutex;
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t->rcu_boost_mutex = NULL;
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}
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#endif /* #ifdef CONFIG_RCU_BOOST */
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/*
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* If this was the last task on the current list, and if
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* we aren't waiting on any CPUs, report the quiescent state.
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* Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
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* so we must take a snapshot of the expedited state.
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*/
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empty_exp_now = !rcu_preempted_readers_exp(rnp);
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if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) {
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trace_rcu_quiescent_state_report("preempt_rcu",
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rnp->gpnum,
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0, rnp->qsmask,
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rnp->level,
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rnp->grplo,
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rnp->grphi,
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!!rnp->gp_tasks);
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rcu_report_unblock_qs_rnp(rnp, flags);
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} else {
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raw_spin_unlock_irqrestore(&rnp->lock, flags);
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}
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#ifdef CONFIG_RCU_BOOST
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/* Unboost if we were boosted. */
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if (rbmp)
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rt_mutex_unlock(rbmp);
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#endif /* #ifdef CONFIG_RCU_BOOST */
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/*
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* If this was the last task on the expedited lists,
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* then we need to report up the rcu_node hierarchy.
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*/
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if (!empty_exp && empty_exp_now)
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rcu_report_exp_rnp(&rcu_preempt_state, rnp, true);
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} else {
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local_irq_restore(flags);
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}
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}
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#ifdef CONFIG_RCU_CPU_STALL_VERBOSE
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/*
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* Dump detailed information for all tasks blocking the current RCU
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* grace period on the specified rcu_node structure.
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*/
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static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
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{
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unsigned long flags;
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struct task_struct *t;
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raw_spin_lock_irqsave(&rnp->lock, flags);
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if (!rcu_preempt_blocked_readers_cgp(rnp)) {
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raw_spin_unlock_irqrestore(&rnp->lock, flags);
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return;
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}
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t = list_entry(rnp->gp_tasks,
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struct task_struct, rcu_node_entry);
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list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
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sched_show_task(t);
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raw_spin_unlock_irqrestore(&rnp->lock, flags);
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}
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/*
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* Dump detailed information for all tasks blocking the current RCU
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* grace period.
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*/
|
|
static void rcu_print_detail_task_stall(struct rcu_state *rsp)
|
|
{
|
|
struct rcu_node *rnp = rcu_get_root(rsp);
|
|
|
|
rcu_print_detail_task_stall_rnp(rnp);
|
|
rcu_for_each_leaf_node(rsp, rnp)
|
|
rcu_print_detail_task_stall_rnp(rnp);
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
|
|
|
|
static void rcu_print_detail_task_stall(struct rcu_state *rsp)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
|
|
|
|
#ifdef CONFIG_RCU_CPU_STALL_INFO
|
|
|
|
static void rcu_print_task_stall_begin(struct rcu_node *rnp)
|
|
{
|
|
printk(KERN_ERR "\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
|
|
rnp->level, rnp->grplo, rnp->grphi);
|
|
}
|
|
|
|
static void rcu_print_task_stall_end(void)
|
|
{
|
|
printk(KERN_CONT "\n");
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
|
|
|
|
static void rcu_print_task_stall_begin(struct rcu_node *rnp)
|
|
{
|
|
}
|
|
|
|
static void rcu_print_task_stall_end(void)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
|
|
|
|
/*
|
|
* Scan the current list of tasks blocked within RCU read-side critical
|
|
* sections, printing out the tid of each.
|
|
*/
|
|
static int rcu_print_task_stall(struct rcu_node *rnp)
|
|
{
|
|
struct task_struct *t;
|
|
int ndetected = 0;
|
|
|
|
if (!rcu_preempt_blocked_readers_cgp(rnp))
|
|
return 0;
|
|
rcu_print_task_stall_begin(rnp);
|
|
t = list_entry(rnp->gp_tasks,
|
|
struct task_struct, rcu_node_entry);
|
|
list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
|
|
printk(KERN_CONT " P%d", t->pid);
|
|
ndetected++;
|
|
}
|
|
rcu_print_task_stall_end();
|
|
return ndetected;
|
|
}
|
|
|
|
/*
|
|
* Check that the list of blocked tasks for the newly completed grace
|
|
* period is in fact empty. It is a serious bug to complete a grace
|
|
* period that still has RCU readers blocked! This function must be
|
|
* invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
|
|
* must be held by the caller.
|
|
*
|
|
* Also, if there are blocked tasks on the list, they automatically
|
|
* block the newly created grace period, so set up ->gp_tasks accordingly.
|
|
*/
|
|
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
|
|
{
|
|
WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
|
|
if (!list_empty(&rnp->blkd_tasks))
|
|
rnp->gp_tasks = rnp->blkd_tasks.next;
|
|
WARN_ON_ONCE(rnp->qsmask);
|
|
}
|
|
|
|
#ifdef CONFIG_HOTPLUG_CPU
|
|
|
|
/*
|
|
* Handle tasklist migration for case in which all CPUs covered by the
|
|
* specified rcu_node have gone offline. Move them up to the root
|
|
* rcu_node. The reason for not just moving them to the immediate
|
|
* parent is to remove the need for rcu_read_unlock_special() to
|
|
* make more than two attempts to acquire the target rcu_node's lock.
|
|
* Returns true if there were tasks blocking the current RCU grace
|
|
* period.
|
|
*
|
|
* Returns 1 if there was previously a task blocking the current grace
|
|
* period on the specified rcu_node structure.
|
|
*
|
|
* The caller must hold rnp->lock with irqs disabled.
|
|
*/
|
|
static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
|
|
struct rcu_node *rnp,
|
|
struct rcu_data *rdp)
|
|
{
|
|
struct list_head *lp;
|
|
struct list_head *lp_root;
|
|
int retval = 0;
|
|
struct rcu_node *rnp_root = rcu_get_root(rsp);
|
|
struct task_struct *t;
|
|
|
|
if (rnp == rnp_root) {
|
|
WARN_ONCE(1, "Last CPU thought to be offlined?");
|
|
return 0; /* Shouldn't happen: at least one CPU online. */
|
|
}
|
|
|
|
/* If we are on an internal node, complain bitterly. */
|
|
WARN_ON_ONCE(rnp != rdp->mynode);
|
|
|
|
/*
|
|
* Move tasks up to root rcu_node. Don't try to get fancy for
|
|
* this corner-case operation -- just put this node's tasks
|
|
* at the head of the root node's list, and update the root node's
|
|
* ->gp_tasks and ->exp_tasks pointers to those of this node's,
|
|
* if non-NULL. This might result in waiting for more tasks than
|
|
* absolutely necessary, but this is a good performance/complexity
|
|
* tradeoff.
|
|
*/
|
|
if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0)
|
|
retval |= RCU_OFL_TASKS_NORM_GP;
|
|
if (rcu_preempted_readers_exp(rnp))
|
|
retval |= RCU_OFL_TASKS_EXP_GP;
|
|
lp = &rnp->blkd_tasks;
|
|
lp_root = &rnp_root->blkd_tasks;
|
|
while (!list_empty(lp)) {
|
|
t = list_entry(lp->next, typeof(*t), rcu_node_entry);
|
|
raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
|
|
list_del(&t->rcu_node_entry);
|
|
t->rcu_blocked_node = rnp_root;
|
|
list_add(&t->rcu_node_entry, lp_root);
|
|
if (&t->rcu_node_entry == rnp->gp_tasks)
|
|
rnp_root->gp_tasks = rnp->gp_tasks;
|
|
if (&t->rcu_node_entry == rnp->exp_tasks)
|
|
rnp_root->exp_tasks = rnp->exp_tasks;
|
|
#ifdef CONFIG_RCU_BOOST
|
|
if (&t->rcu_node_entry == rnp->boost_tasks)
|
|
rnp_root->boost_tasks = rnp->boost_tasks;
|
|
#endif /* #ifdef CONFIG_RCU_BOOST */
|
|
raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
|
|
}
|
|
|
|
rnp->gp_tasks = NULL;
|
|
rnp->exp_tasks = NULL;
|
|
#ifdef CONFIG_RCU_BOOST
|
|
rnp->boost_tasks = NULL;
|
|
/*
|
|
* In case root is being boosted and leaf was not. Make sure
|
|
* that we boost the tasks blocking the current grace period
|
|
* in this case.
|
|
*/
|
|
raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
|
|
if (rnp_root->boost_tasks != NULL &&
|
|
rnp_root->boost_tasks != rnp_root->gp_tasks &&
|
|
rnp_root->boost_tasks != rnp_root->exp_tasks)
|
|
rnp_root->boost_tasks = rnp_root->gp_tasks;
|
|
raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
|
|
#endif /* #ifdef CONFIG_RCU_BOOST */
|
|
|
|
return retval;
|
|
}
|
|
|
|
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
|
|
|
|
/*
|
|
* Check for a quiescent state from the current CPU. When a task blocks,
|
|
* the task is recorded in the corresponding CPU's rcu_node structure,
|
|
* which is checked elsewhere.
|
|
*
|
|
* Caller must disable hard irqs.
|
|
*/
|
|
static void rcu_preempt_check_callbacks(int cpu)
|
|
{
|
|
struct task_struct *t = current;
|
|
|
|
if (t->rcu_read_lock_nesting == 0) {
|
|
rcu_preempt_qs(cpu);
|
|
return;
|
|
}
|
|
if (t->rcu_read_lock_nesting > 0 &&
|
|
per_cpu(rcu_preempt_data, cpu).qs_pending)
|
|
t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
|
|
}
|
|
|
|
#ifdef CONFIG_RCU_BOOST
|
|
|
|
static void rcu_preempt_do_callbacks(void)
|
|
{
|
|
rcu_do_batch(&rcu_preempt_state, &__get_cpu_var(rcu_preempt_data));
|
|
}
|
|
|
|
#endif /* #ifdef CONFIG_RCU_BOOST */
|
|
|
|
/*
|
|
* Queue a preemptible-RCU callback for invocation after a grace period.
|
|
*/
|
|
void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
|
|
{
|
|
__call_rcu(head, func, &rcu_preempt_state, -1, 0);
|
|
}
|
|
EXPORT_SYMBOL_GPL(call_rcu);
|
|
|
|
/*
|
|
* Queue an RCU callback for lazy invocation after a grace period.
|
|
* This will likely be later named something like "call_rcu_lazy()",
|
|
* but this change will require some way of tagging the lazy RCU
|
|
* callbacks in the list of pending callbacks. Until then, this
|
|
* function may only be called from __kfree_rcu().
|
|
*/
|
|
void kfree_call_rcu(struct rcu_head *head,
|
|
void (*func)(struct rcu_head *rcu))
|
|
{
|
|
__call_rcu(head, func, &rcu_preempt_state, -1, 1);
|
|
}
|
|
EXPORT_SYMBOL_GPL(kfree_call_rcu);
|
|
|
|
/**
|
|
* synchronize_rcu - wait until a grace period has elapsed.
|
|
*
|
|
* Control will return to the caller some time after a full grace
|
|
* period has elapsed, in other words after all currently executing RCU
|
|
* read-side critical sections have completed. Note, however, that
|
|
* upon return from synchronize_rcu(), the caller might well be executing
|
|
* concurrently with new RCU read-side critical sections that began while
|
|
* synchronize_rcu() was waiting. RCU read-side critical sections are
|
|
* delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
|
|
*
|
|
* See the description of synchronize_sched() for more detailed information
|
|
* on memory ordering guarantees.
|
|
*/
|
|
void synchronize_rcu(void)
|
|
{
|
|
rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
|
|
!lock_is_held(&rcu_lock_map) &&
|
|
!lock_is_held(&rcu_sched_lock_map),
|
|
"Illegal synchronize_rcu() in RCU read-side critical section");
|
|
if (!rcu_scheduler_active)
|
|
return;
|
|
if (rcu_expedited)
|
|
synchronize_rcu_expedited();
|
|
else
|
|
wait_rcu_gp(call_rcu);
|
|
}
|
|
EXPORT_SYMBOL_GPL(synchronize_rcu);
|
|
|
|
static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
|
|
static unsigned long sync_rcu_preempt_exp_count;
|
|
static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
|
|
|
|
/*
|
|
* Return non-zero if there are any tasks in RCU read-side critical
|
|
* sections blocking the current preemptible-RCU expedited grace period.
|
|
* If there is no preemptible-RCU expedited grace period currently in
|
|
* progress, returns zero unconditionally.
|
|
*/
|
|
static int rcu_preempted_readers_exp(struct rcu_node *rnp)
|
|
{
|
|
return rnp->exp_tasks != NULL;
|
|
}
|
|
|
|
/*
|
|
* return non-zero if there is no RCU expedited grace period in progress
|
|
* for the specified rcu_node structure, in other words, if all CPUs and
|
|
* tasks covered by the specified rcu_node structure have done their bit
|
|
* for the current expedited grace period. Works only for preemptible
|
|
* RCU -- other RCU implementation use other means.
|
|
*
|
|
* Caller must hold sync_rcu_preempt_exp_mutex.
|
|
*/
|
|
static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
|
|
{
|
|
return !rcu_preempted_readers_exp(rnp) &&
|
|
ACCESS_ONCE(rnp->expmask) == 0;
|
|
}
|
|
|
|
/*
|
|
* Report the exit from RCU read-side critical section for the last task
|
|
* that queued itself during or before the current expedited preemptible-RCU
|
|
* grace period. This event is reported either to the rcu_node structure on
|
|
* which the task was queued or to one of that rcu_node structure's ancestors,
|
|
* recursively up the tree. (Calm down, calm down, we do the recursion
|
|
* iteratively!)
|
|
*
|
|
* Most callers will set the "wake" flag, but the task initiating the
|
|
* expedited grace period need not wake itself.
|
|
*
|
|
* Caller must hold sync_rcu_preempt_exp_mutex.
|
|
*/
|
|
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
|
|
bool wake)
|
|
{
|
|
unsigned long flags;
|
|
unsigned long mask;
|
|
|
|
raw_spin_lock_irqsave(&rnp->lock, flags);
|
|
for (;;) {
|
|
if (!sync_rcu_preempt_exp_done(rnp)) {
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
break;
|
|
}
|
|
if (rnp->parent == NULL) {
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
if (wake)
|
|
wake_up(&sync_rcu_preempt_exp_wq);
|
|
break;
|
|
}
|
|
mask = rnp->grpmask;
|
|
raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
|
|
rnp = rnp->parent;
|
|
raw_spin_lock(&rnp->lock); /* irqs already disabled */
|
|
rnp->expmask &= ~mask;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Snapshot the tasks blocking the newly started preemptible-RCU expedited
|
|
* grace period for the specified rcu_node structure. If there are no such
|
|
* tasks, report it up the rcu_node hierarchy.
|
|
*
|
|
* Caller must hold sync_rcu_preempt_exp_mutex and must exclude
|
|
* CPU hotplug operations.
|
|
*/
|
|
static void
|
|
sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
|
|
{
|
|
unsigned long flags;
|
|
int must_wait = 0;
|
|
|
|
raw_spin_lock_irqsave(&rnp->lock, flags);
|
|
if (list_empty(&rnp->blkd_tasks)) {
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
} else {
|
|
rnp->exp_tasks = rnp->blkd_tasks.next;
|
|
rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
|
|
must_wait = 1;
|
|
}
|
|
if (!must_wait)
|
|
rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */
|
|
}
|
|
|
|
/**
|
|
* synchronize_rcu_expedited - Brute-force RCU grace period
|
|
*
|
|
* Wait for an RCU-preempt grace period, but expedite it. The basic
|
|
* idea is to invoke synchronize_sched_expedited() to push all the tasks to
|
|
* the ->blkd_tasks lists and wait for this list to drain. This consumes
|
|
* significant time on all CPUs and is unfriendly to real-time workloads,
|
|
* so is thus not recommended for any sort of common-case code.
|
|
* In fact, if you are using synchronize_rcu_expedited() in a loop,
|
|
* please restructure your code to batch your updates, and then Use a
|
|
* single synchronize_rcu() instead.
|
|
*
|
|
* Note that it is illegal to call this function while holding any lock
|
|
* that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
|
|
* to call this function from a CPU-hotplug notifier. Failing to observe
|
|
* these restriction will result in deadlock.
|
|
*/
|
|
void synchronize_rcu_expedited(void)
|
|
{
|
|
unsigned long flags;
|
|
struct rcu_node *rnp;
|
|
struct rcu_state *rsp = &rcu_preempt_state;
|
|
unsigned long snap;
|
|
int trycount = 0;
|
|
|
|
smp_mb(); /* Caller's modifications seen first by other CPUs. */
|
|
snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1;
|
|
smp_mb(); /* Above access cannot bleed into critical section. */
|
|
|
|
/*
|
|
* Block CPU-hotplug operations. This means that any CPU-hotplug
|
|
* operation that finds an rcu_node structure with tasks in the
|
|
* process of being boosted will know that all tasks blocking
|
|
* this expedited grace period will already be in the process of
|
|
* being boosted. This simplifies the process of moving tasks
|
|
* from leaf to root rcu_node structures.
|
|
*/
|
|
get_online_cpus();
|
|
|
|
/*
|
|
* Acquire lock, falling back to synchronize_rcu() if too many
|
|
* lock-acquisition failures. Of course, if someone does the
|
|
* expedited grace period for us, just leave.
|
|
*/
|
|
while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {
|
|
if (ULONG_CMP_LT(snap,
|
|
ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
|
|
put_online_cpus();
|
|
goto mb_ret; /* Others did our work for us. */
|
|
}
|
|
if (trycount++ < 10) {
|
|
udelay(trycount * num_online_cpus());
|
|
} else {
|
|
put_online_cpus();
|
|
wait_rcu_gp(call_rcu);
|
|
return;
|
|
}
|
|
}
|
|
if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
|
|
put_online_cpus();
|
|
goto unlock_mb_ret; /* Others did our work for us. */
|
|
}
|
|
|
|
/* force all RCU readers onto ->blkd_tasks lists. */
|
|
synchronize_sched_expedited();
|
|
|
|
/* Initialize ->expmask for all non-leaf rcu_node structures. */
|
|
rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
|
|
raw_spin_lock_irqsave(&rnp->lock, flags);
|
|
rnp->expmask = rnp->qsmaskinit;
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
}
|
|
|
|
/* Snapshot current state of ->blkd_tasks lists. */
|
|
rcu_for_each_leaf_node(rsp, rnp)
|
|
sync_rcu_preempt_exp_init(rsp, rnp);
|
|
if (NUM_RCU_NODES > 1)
|
|
sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp));
|
|
|
|
put_online_cpus();
|
|
|
|
/* Wait for snapshotted ->blkd_tasks lists to drain. */
|
|
rnp = rcu_get_root(rsp);
|
|
wait_event(sync_rcu_preempt_exp_wq,
|
|
sync_rcu_preempt_exp_done(rnp));
|
|
|
|
/* Clean up and exit. */
|
|
smp_mb(); /* ensure expedited GP seen before counter increment. */
|
|
ACCESS_ONCE(sync_rcu_preempt_exp_count)++;
|
|
unlock_mb_ret:
|
|
mutex_unlock(&sync_rcu_preempt_exp_mutex);
|
|
mb_ret:
|
|
smp_mb(); /* ensure subsequent action seen after grace period. */
|
|
}
|
|
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
|
|
|
|
/**
|
|
* rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
|
|
*
|
|
* Note that this primitive does not necessarily wait for an RCU grace period
|
|
* to complete. For example, if there are no RCU callbacks queued anywhere
|
|
* in the system, then rcu_barrier() is within its rights to return
|
|
* immediately, without waiting for anything, much less an RCU grace period.
|
|
*/
|
|
void rcu_barrier(void)
|
|
{
|
|
_rcu_barrier(&rcu_preempt_state);
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_barrier);
|
|
|
|
/*
|
|
* Initialize preemptible RCU's state structures.
|
|
*/
|
|
static void __init __rcu_init_preempt(void)
|
|
{
|
|
rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
|
|
|
|
static struct rcu_state *rcu_state = &rcu_sched_state;
|
|
|
|
/*
|
|
* Tell them what RCU they are running.
|
|
*/
|
|
static void __init rcu_bootup_announce(void)
|
|
{
|
|
printk(KERN_INFO "Hierarchical RCU implementation.\n");
|
|
rcu_bootup_announce_oddness();
|
|
}
|
|
|
|
/*
|
|
* Return the number of RCU batches processed thus far for debug & stats.
|
|
*/
|
|
long rcu_batches_completed(void)
|
|
{
|
|
return rcu_batches_completed_sched();
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_batches_completed);
|
|
|
|
/*
|
|
* Force a quiescent state for RCU, which, because there is no preemptible
|
|
* RCU, becomes the same as rcu-sched.
|
|
*/
|
|
void rcu_force_quiescent_state(void)
|
|
{
|
|
rcu_sched_force_quiescent_state();
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, we never have to check for
|
|
* CPUs being in quiescent states.
|
|
*/
|
|
static void rcu_preempt_note_context_switch(int cpu)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, there are never any preempted
|
|
* RCU readers.
|
|
*/
|
|
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
#ifdef CONFIG_HOTPLUG_CPU
|
|
|
|
/* Because preemptible RCU does not exist, no quieting of tasks. */
|
|
static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
|
|
{
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
}
|
|
|
|
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, we never have to check for
|
|
* tasks blocked within RCU read-side critical sections.
|
|
*/
|
|
static void rcu_print_detail_task_stall(struct rcu_state *rsp)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, we never have to check for
|
|
* tasks blocked within RCU read-side critical sections.
|
|
*/
|
|
static int rcu_print_task_stall(struct rcu_node *rnp)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Because there is no preemptible RCU, there can be no readers blocked,
|
|
* so there is no need to check for blocked tasks. So check only for
|
|
* bogus qsmask values.
|
|
*/
|
|
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
|
|
{
|
|
WARN_ON_ONCE(rnp->qsmask);
|
|
}
|
|
|
|
#ifdef CONFIG_HOTPLUG_CPU
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, it never needs to migrate
|
|
* tasks that were blocked within RCU read-side critical sections, and
|
|
* such non-existent tasks cannot possibly have been blocking the current
|
|
* grace period.
|
|
*/
|
|
static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
|
|
struct rcu_node *rnp,
|
|
struct rcu_data *rdp)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, it never has any callbacks
|
|
* to check.
|
|
*/
|
|
static void rcu_preempt_check_callbacks(int cpu)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Queue an RCU callback for lazy invocation after a grace period.
|
|
* This will likely be later named something like "call_rcu_lazy()",
|
|
* but this change will require some way of tagging the lazy RCU
|
|
* callbacks in the list of pending callbacks. Until then, this
|
|
* function may only be called from __kfree_rcu().
|
|
*
|
|
* Because there is no preemptible RCU, we use RCU-sched instead.
|
|
*/
|
|
void kfree_call_rcu(struct rcu_head *head,
|
|
void (*func)(struct rcu_head *rcu))
|
|
{
|
|
__call_rcu(head, func, &rcu_sched_state, -1, 1);
|
|
}
|
|
EXPORT_SYMBOL_GPL(kfree_call_rcu);
|
|
|
|
/*
|
|
* Wait for an rcu-preempt grace period, but make it happen quickly.
|
|
* But because preemptible RCU does not exist, map to rcu-sched.
|
|
*/
|
|
void synchronize_rcu_expedited(void)
|
|
{
|
|
synchronize_sched_expedited();
|
|
}
|
|
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
|
|
|
|
#ifdef CONFIG_HOTPLUG_CPU
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, there is never any need to
|
|
* report on tasks preempted in RCU read-side critical sections during
|
|
* expedited RCU grace periods.
|
|
*/
|
|
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
|
|
bool wake)
|
|
{
|
|
}
|
|
|
|
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, rcu_barrier() is just
|
|
* another name for rcu_barrier_sched().
|
|
*/
|
|
void rcu_barrier(void)
|
|
{
|
|
rcu_barrier_sched();
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_barrier);
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, it need not be initialized.
|
|
*/
|
|
static void __init __rcu_init_preempt(void)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
|
|
|
|
#ifdef CONFIG_RCU_BOOST
|
|
|
|
#include "rtmutex_common.h"
|
|
|
|
#ifdef CONFIG_RCU_TRACE
|
|
|
|
static void rcu_initiate_boost_trace(struct rcu_node *rnp)
|
|
{
|
|
if (list_empty(&rnp->blkd_tasks))
|
|
rnp->n_balk_blkd_tasks++;
|
|
else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL)
|
|
rnp->n_balk_exp_gp_tasks++;
|
|
else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL)
|
|
rnp->n_balk_boost_tasks++;
|
|
else if (rnp->gp_tasks != NULL && rnp->qsmask != 0)
|
|
rnp->n_balk_notblocked++;
|
|
else if (rnp->gp_tasks != NULL &&
|
|
ULONG_CMP_LT(jiffies, rnp->boost_time))
|
|
rnp->n_balk_notyet++;
|
|
else
|
|
rnp->n_balk_nos++;
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_RCU_TRACE */
|
|
|
|
static void rcu_initiate_boost_trace(struct rcu_node *rnp)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_TRACE */
|
|
|
|
static void rcu_wake_cond(struct task_struct *t, int status)
|
|
{
|
|
/*
|
|
* If the thread is yielding, only wake it when this
|
|
* is invoked from idle
|
|
*/
|
|
if (status != RCU_KTHREAD_YIELDING || is_idle_task(current))
|
|
wake_up_process(t);
|
|
}
|
|
|
|
/*
|
|
* Carry out RCU priority boosting on the task indicated by ->exp_tasks
|
|
* or ->boost_tasks, advancing the pointer to the next task in the
|
|
* ->blkd_tasks list.
|
|
*
|
|
* Note that irqs must be enabled: boosting the task can block.
|
|
* Returns 1 if there are more tasks needing to be boosted.
|
|
*/
|
|
static int rcu_boost(struct rcu_node *rnp)
|
|
{
|
|
unsigned long flags;
|
|
struct rt_mutex mtx;
|
|
struct task_struct *t;
|
|
struct list_head *tb;
|
|
|
|
if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL)
|
|
return 0; /* Nothing left to boost. */
|
|
|
|
raw_spin_lock_irqsave(&rnp->lock, flags);
|
|
|
|
/*
|
|
* Recheck under the lock: all tasks in need of boosting
|
|
* might exit their RCU read-side critical sections on their own.
|
|
*/
|
|
if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Preferentially boost tasks blocking expedited grace periods.
|
|
* This cannot starve the normal grace periods because a second
|
|
* expedited grace period must boost all blocked tasks, including
|
|
* those blocking the pre-existing normal grace period.
|
|
*/
|
|
if (rnp->exp_tasks != NULL) {
|
|
tb = rnp->exp_tasks;
|
|
rnp->n_exp_boosts++;
|
|
} else {
|
|
tb = rnp->boost_tasks;
|
|
rnp->n_normal_boosts++;
|
|
}
|
|
rnp->n_tasks_boosted++;
|
|
|
|
/*
|
|
* We boost task t by manufacturing an rt_mutex that appears to
|
|
* be held by task t. We leave a pointer to that rt_mutex where
|
|
* task t can find it, and task t will release the mutex when it
|
|
* exits its outermost RCU read-side critical section. Then
|
|
* simply acquiring this artificial rt_mutex will boost task
|
|
* t's priority. (Thanks to tglx for suggesting this approach!)
|
|
*
|
|
* Note that task t must acquire rnp->lock to remove itself from
|
|
* the ->blkd_tasks list, which it will do from exit() if from
|
|
* nowhere else. We therefore are guaranteed that task t will
|
|
* stay around at least until we drop rnp->lock. Note that
|
|
* rnp->lock also resolves races between our priority boosting
|
|
* and task t's exiting its outermost RCU read-side critical
|
|
* section.
|
|
*/
|
|
t = container_of(tb, struct task_struct, rcu_node_entry);
|
|
rt_mutex_init_proxy_locked(&mtx, t);
|
|
t->rcu_boost_mutex = &mtx;
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
rt_mutex_lock(&mtx); /* Side effect: boosts task t's priority. */
|
|
rt_mutex_unlock(&mtx); /* Keep lockdep happy. */
|
|
|
|
return ACCESS_ONCE(rnp->exp_tasks) != NULL ||
|
|
ACCESS_ONCE(rnp->boost_tasks) != NULL;
|
|
}
|
|
|
|
/*
|
|
* Priority-boosting kthread. One per leaf rcu_node and one for the
|
|
* root rcu_node.
|
|
*/
|
|
static int rcu_boost_kthread(void *arg)
|
|
{
|
|
struct rcu_node *rnp = (struct rcu_node *)arg;
|
|
int spincnt = 0;
|
|
int more2boost;
|
|
|
|
trace_rcu_utilization("Start boost kthread@init");
|
|
for (;;) {
|
|
rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
|
|
trace_rcu_utilization("End boost kthread@rcu_wait");
|
|
rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
|
|
trace_rcu_utilization("Start boost kthread@rcu_wait");
|
|
rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
|
|
more2boost = rcu_boost(rnp);
|
|
if (more2boost)
|
|
spincnt++;
|
|
else
|
|
spincnt = 0;
|
|
if (spincnt > 10) {
|
|
rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
|
|
trace_rcu_utilization("End boost kthread@rcu_yield");
|
|
schedule_timeout_interruptible(2);
|
|
trace_rcu_utilization("Start boost kthread@rcu_yield");
|
|
spincnt = 0;
|
|
}
|
|
}
|
|
/* NOTREACHED */
|
|
trace_rcu_utilization("End boost kthread@notreached");
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Check to see if it is time to start boosting RCU readers that are
|
|
* blocking the current grace period, and, if so, tell the per-rcu_node
|
|
* kthread to start boosting them. If there is an expedited grace
|
|
* period in progress, it is always time to boost.
|
|
*
|
|
* The caller must hold rnp->lock, which this function releases.
|
|
* The ->boost_kthread_task is immortal, so we don't need to worry
|
|
* about it going away.
|
|
*/
|
|
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
|
|
{
|
|
struct task_struct *t;
|
|
|
|
if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
|
|
rnp->n_balk_exp_gp_tasks++;
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
return;
|
|
}
|
|
if (rnp->exp_tasks != NULL ||
|
|
(rnp->gp_tasks != NULL &&
|
|
rnp->boost_tasks == NULL &&
|
|
rnp->qsmask == 0 &&
|
|
ULONG_CMP_GE(jiffies, rnp->boost_time))) {
|
|
if (rnp->exp_tasks == NULL)
|
|
rnp->boost_tasks = rnp->gp_tasks;
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
t = rnp->boost_kthread_task;
|
|
if (t)
|
|
rcu_wake_cond(t, rnp->boost_kthread_status);
|
|
} else {
|
|
rcu_initiate_boost_trace(rnp);
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Wake up the per-CPU kthread to invoke RCU callbacks.
|
|
*/
|
|
static void invoke_rcu_callbacks_kthread(void)
|
|
{
|
|
unsigned long flags;
|
|
|
|
local_irq_save(flags);
|
|
__this_cpu_write(rcu_cpu_has_work, 1);
|
|
if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
|
|
current != __this_cpu_read(rcu_cpu_kthread_task)) {
|
|
rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task),
|
|
__this_cpu_read(rcu_cpu_kthread_status));
|
|
}
|
|
local_irq_restore(flags);
|
|
}
|
|
|
|
/*
|
|
* Is the current CPU running the RCU-callbacks kthread?
|
|
* Caller must have preemption disabled.
|
|
*/
|
|
static bool rcu_is_callbacks_kthread(void)
|
|
{
|
|
return __get_cpu_var(rcu_cpu_kthread_task) == current;
|
|
}
|
|
|
|
#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
|
|
|
|
/*
|
|
* Do priority-boost accounting for the start of a new grace period.
|
|
*/
|
|
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
|
|
{
|
|
rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
|
|
}
|
|
|
|
/*
|
|
* Create an RCU-boost kthread for the specified node if one does not
|
|
* already exist. We only create this kthread for preemptible RCU.
|
|
* Returns zero if all is well, a negated errno otherwise.
|
|
*/
|
|
static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
|
|
struct rcu_node *rnp)
|
|
{
|
|
int rnp_index = rnp - &rsp->node[0];
|
|
unsigned long flags;
|
|
struct sched_param sp;
|
|
struct task_struct *t;
|
|
|
|
if (&rcu_preempt_state != rsp)
|
|
return 0;
|
|
|
|
if (!rcu_scheduler_fully_active || rnp->qsmaskinit == 0)
|
|
return 0;
|
|
|
|
rsp->boost = 1;
|
|
if (rnp->boost_kthread_task != NULL)
|
|
return 0;
|
|
t = kthread_create(rcu_boost_kthread, (void *)rnp,
|
|
"rcub/%d", rnp_index);
|
|
if (IS_ERR(t))
|
|
return PTR_ERR(t);
|
|
raw_spin_lock_irqsave(&rnp->lock, flags);
|
|
rnp->boost_kthread_task = t;
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
sp.sched_priority = RCU_BOOST_PRIO;
|
|
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
|
|
wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
|
|
return 0;
|
|
}
|
|
|
|
static void rcu_kthread_do_work(void)
|
|
{
|
|
rcu_do_batch(&rcu_sched_state, &__get_cpu_var(rcu_sched_data));
|
|
rcu_do_batch(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
|
|
rcu_preempt_do_callbacks();
|
|
}
|
|
|
|
static void rcu_cpu_kthread_setup(unsigned int cpu)
|
|
{
|
|
struct sched_param sp;
|
|
|
|
sp.sched_priority = RCU_KTHREAD_PRIO;
|
|
sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
|
|
}
|
|
|
|
static void rcu_cpu_kthread_park(unsigned int cpu)
|
|
{
|
|
per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
|
|
}
|
|
|
|
static int rcu_cpu_kthread_should_run(unsigned int cpu)
|
|
{
|
|
return __get_cpu_var(rcu_cpu_has_work);
|
|
}
|
|
|
|
/*
|
|
* Per-CPU kernel thread that invokes RCU callbacks. This replaces the
|
|
* RCU softirq used in flavors and configurations of RCU that do not
|
|
* support RCU priority boosting.
|
|
*/
|
|
static void rcu_cpu_kthread(unsigned int cpu)
|
|
{
|
|
unsigned int *statusp = &__get_cpu_var(rcu_cpu_kthread_status);
|
|
char work, *workp = &__get_cpu_var(rcu_cpu_has_work);
|
|
int spincnt;
|
|
|
|
for (spincnt = 0; spincnt < 10; spincnt++) {
|
|
trace_rcu_utilization("Start CPU kthread@rcu_wait");
|
|
local_bh_disable();
|
|
*statusp = RCU_KTHREAD_RUNNING;
|
|
this_cpu_inc(rcu_cpu_kthread_loops);
|
|
local_irq_disable();
|
|
work = *workp;
|
|
*workp = 0;
|
|
local_irq_enable();
|
|
if (work)
|
|
rcu_kthread_do_work();
|
|
local_bh_enable();
|
|
if (*workp == 0) {
|
|
trace_rcu_utilization("End CPU kthread@rcu_wait");
|
|
*statusp = RCU_KTHREAD_WAITING;
|
|
return;
|
|
}
|
|
}
|
|
*statusp = RCU_KTHREAD_YIELDING;
|
|
trace_rcu_utilization("Start CPU kthread@rcu_yield");
|
|
schedule_timeout_interruptible(2);
|
|
trace_rcu_utilization("End CPU kthread@rcu_yield");
|
|
*statusp = RCU_KTHREAD_WAITING;
|
|
}
|
|
|
|
/*
|
|
* Set the per-rcu_node kthread's affinity to cover all CPUs that are
|
|
* served by the rcu_node in question. The CPU hotplug lock is still
|
|
* held, so the value of rnp->qsmaskinit will be stable.
|
|
*
|
|
* We don't include outgoingcpu in the affinity set, use -1 if there is
|
|
* no outgoing CPU. If there are no CPUs left in the affinity set,
|
|
* this function allows the kthread to execute on any CPU.
|
|
*/
|
|
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
|
|
{
|
|
struct task_struct *t = rnp->boost_kthread_task;
|
|
unsigned long mask = rnp->qsmaskinit;
|
|
cpumask_var_t cm;
|
|
int cpu;
|
|
|
|
if (!t)
|
|
return;
|
|
if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
|
|
return;
|
|
for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
|
|
if ((mask & 0x1) && cpu != outgoingcpu)
|
|
cpumask_set_cpu(cpu, cm);
|
|
if (cpumask_weight(cm) == 0) {
|
|
cpumask_setall(cm);
|
|
for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++)
|
|
cpumask_clear_cpu(cpu, cm);
|
|
WARN_ON_ONCE(cpumask_weight(cm) == 0);
|
|
}
|
|
set_cpus_allowed_ptr(t, cm);
|
|
free_cpumask_var(cm);
|
|
}
|
|
|
|
static struct smp_hotplug_thread rcu_cpu_thread_spec = {
|
|
.store = &rcu_cpu_kthread_task,
|
|
.thread_should_run = rcu_cpu_kthread_should_run,
|
|
.thread_fn = rcu_cpu_kthread,
|
|
.thread_comm = "rcuc/%u",
|
|
.setup = rcu_cpu_kthread_setup,
|
|
.park = rcu_cpu_kthread_park,
|
|
};
|
|
|
|
/*
|
|
* Spawn all kthreads -- called as soon as the scheduler is running.
|
|
*/
|
|
static int __init rcu_spawn_kthreads(void)
|
|
{
|
|
struct rcu_node *rnp;
|
|
int cpu;
|
|
|
|
rcu_scheduler_fully_active = 1;
|
|
for_each_possible_cpu(cpu)
|
|
per_cpu(rcu_cpu_has_work, cpu) = 0;
|
|
BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
|
|
rnp = rcu_get_root(rcu_state);
|
|
(void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
|
|
if (NUM_RCU_NODES > 1) {
|
|
rcu_for_each_leaf_node(rcu_state, rnp)
|
|
(void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
|
|
}
|
|
return 0;
|
|
}
|
|
early_initcall(rcu_spawn_kthreads);
|
|
|
|
static void __cpuinit rcu_prepare_kthreads(int cpu)
|
|
{
|
|
struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
|
|
struct rcu_node *rnp = rdp->mynode;
|
|
|
|
/* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
|
|
if (rcu_scheduler_fully_active)
|
|
(void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_RCU_BOOST */
|
|
|
|
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
|
|
{
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
}
|
|
|
|
static void invoke_rcu_callbacks_kthread(void)
|
|
{
|
|
WARN_ON_ONCE(1);
|
|
}
|
|
|
|
static bool rcu_is_callbacks_kthread(void)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
|
|
{
|
|
}
|
|
|
|
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
|
|
{
|
|
}
|
|
|
|
static int __init rcu_scheduler_really_started(void)
|
|
{
|
|
rcu_scheduler_fully_active = 1;
|
|
return 0;
|
|
}
|
|
early_initcall(rcu_scheduler_really_started);
|
|
|
|
static void __cpuinit rcu_prepare_kthreads(int cpu)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_BOOST */
|
|
|
|
#if !defined(CONFIG_RCU_FAST_NO_HZ)
|
|
|
|
/*
|
|
* Check to see if any future RCU-related work will need to be done
|
|
* by the current CPU, even if none need be done immediately, returning
|
|
* 1 if so. This function is part of the RCU implementation; it is -not-
|
|
* an exported member of the RCU API.
|
|
*
|
|
* Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
|
|
* any flavor of RCU.
|
|
*/
|
|
int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
|
|
{
|
|
*delta_jiffies = ULONG_MAX;
|
|
return rcu_cpu_has_callbacks(cpu);
|
|
}
|
|
|
|
/*
|
|
* Because we do not have RCU_FAST_NO_HZ, don't bother initializing for it.
|
|
*/
|
|
static void rcu_prepare_for_idle_init(int cpu)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
|
|
* after it.
|
|
*/
|
|
static void rcu_cleanup_after_idle(int cpu)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
|
|
* is nothing.
|
|
*/
|
|
static void rcu_prepare_for_idle(int cpu)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Don't bother keeping a running count of the number of RCU callbacks
|
|
* posted because CONFIG_RCU_FAST_NO_HZ=n.
|
|
*/
|
|
static void rcu_idle_count_callbacks_posted(void)
|
|
{
|
|
}
|
|
|
|
#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
|
|
|
|
/*
|
|
* This code is invoked when a CPU goes idle, at which point we want
|
|
* to have the CPU do everything required for RCU so that it can enter
|
|
* the energy-efficient dyntick-idle mode. This is handled by a
|
|
* state machine implemented by rcu_prepare_for_idle() below.
|
|
*
|
|
* The following three proprocessor symbols control this state machine:
|
|
*
|
|
* RCU_IDLE_FLUSHES gives the maximum number of times that we will attempt
|
|
* to satisfy RCU. Beyond this point, it is better to incur a periodic
|
|
* scheduling-clock interrupt than to loop through the state machine
|
|
* at full power.
|
|
* RCU_IDLE_OPT_FLUSHES gives the number of RCU_IDLE_FLUSHES that are
|
|
* optional if RCU does not need anything immediately from this
|
|
* CPU, even if this CPU still has RCU callbacks queued. The first
|
|
* times through the state machine are mandatory: we need to give
|
|
* the state machine a chance to communicate a quiescent state
|
|
* to the RCU core.
|
|
* RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
|
|
* to sleep in dyntick-idle mode with RCU callbacks pending. This
|
|
* is sized to be roughly one RCU grace period. Those energy-efficiency
|
|
* benchmarkers who might otherwise be tempted to set this to a large
|
|
* number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
|
|
* system. And if you are -that- concerned about energy efficiency,
|
|
* just power the system down and be done with it!
|
|
* RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
|
|
* permitted to sleep in dyntick-idle mode with only lazy RCU
|
|
* callbacks pending. Setting this too high can OOM your system.
|
|
*
|
|
* The values below work well in practice. If future workloads require
|
|
* adjustment, they can be converted into kernel config parameters, though
|
|
* making the state machine smarter might be a better option.
|
|
*/
|
|
#define RCU_IDLE_FLUSHES 5 /* Number of dyntick-idle tries. */
|
|
#define RCU_IDLE_OPT_FLUSHES 3 /* Optional dyntick-idle tries. */
|
|
#define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
|
|
#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
|
|
|
|
extern int tick_nohz_enabled;
|
|
|
|
/*
|
|
* Does the specified flavor of RCU have non-lazy callbacks pending on
|
|
* the specified CPU? Both RCU flavor and CPU are specified by the
|
|
* rcu_data structure.
|
|
*/
|
|
static bool __rcu_cpu_has_nonlazy_callbacks(struct rcu_data *rdp)
|
|
{
|
|
return rdp->qlen != rdp->qlen_lazy;
|
|
}
|
|
|
|
#ifdef CONFIG_TREE_PREEMPT_RCU
|
|
|
|
/*
|
|
* Are there non-lazy RCU-preempt callbacks? (There cannot be if there
|
|
* is no RCU-preempt in the kernel.)
|
|
*/
|
|
static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu)
|
|
{
|
|
struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
|
|
|
|
return __rcu_cpu_has_nonlazy_callbacks(rdp);
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
|
|
|
|
static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
#endif /* else #ifdef CONFIG_TREE_PREEMPT_RCU */
|
|
|
|
/*
|
|
* Does any flavor of RCU have non-lazy callbacks on the specified CPU?
|
|
*/
|
|
static bool rcu_cpu_has_nonlazy_callbacks(int cpu)
|
|
{
|
|
return __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_sched_data, cpu)) ||
|
|
__rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_bh_data, cpu)) ||
|
|
rcu_preempt_cpu_has_nonlazy_callbacks(cpu);
|
|
}
|
|
|
|
/*
|
|
* Allow the CPU to enter dyntick-idle mode if either: (1) There are no
|
|
* callbacks on this CPU, (2) this CPU has not yet attempted to enter
|
|
* dyntick-idle mode, or (3) this CPU is in the process of attempting to
|
|
* enter dyntick-idle mode. Otherwise, if we have recently tried and failed
|
|
* to enter dyntick-idle mode, we refuse to try to enter it. After all,
|
|
* it is better to incur scheduling-clock interrupts than to spin
|
|
* continuously for the same time duration!
|
|
*
|
|
* The delta_jiffies argument is used to store the time when RCU is
|
|
* going to need the CPU again if it still has callbacks. The reason
|
|
* for this is that rcu_prepare_for_idle() might need to post a timer,
|
|
* but if so, it will do so after tick_nohz_stop_sched_tick() has set
|
|
* the wakeup time for this CPU. This means that RCU's timer can be
|
|
* delayed until the wakeup time, which defeats the purpose of posting
|
|
* a timer.
|
|
*/
|
|
int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
|
|
{
|
|
struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
|
|
|
|
/* Flag a new idle sojourn to the idle-entry state machine. */
|
|
rdtp->idle_first_pass = 1;
|
|
/* If no callbacks, RCU doesn't need the CPU. */
|
|
if (!rcu_cpu_has_callbacks(cpu)) {
|
|
*delta_jiffies = ULONG_MAX;
|
|
return 0;
|
|
}
|
|
if (rdtp->dyntick_holdoff == jiffies) {
|
|
/* RCU recently tried and failed, so don't try again. */
|
|
*delta_jiffies = 1;
|
|
return 1;
|
|
}
|
|
/* Set up for the possibility that RCU will post a timer. */
|
|
if (rcu_cpu_has_nonlazy_callbacks(cpu)) {
|
|
*delta_jiffies = round_up(RCU_IDLE_GP_DELAY + jiffies,
|
|
RCU_IDLE_GP_DELAY) - jiffies;
|
|
} else {
|
|
*delta_jiffies = jiffies + RCU_IDLE_LAZY_GP_DELAY;
|
|
*delta_jiffies = round_jiffies(*delta_jiffies) - jiffies;
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Handler for smp_call_function_single(). The only point of this
|
|
* handler is to wake the CPU up, so the handler does only tracing.
|
|
*/
|
|
void rcu_idle_demigrate(void *unused)
|
|
{
|
|
trace_rcu_prep_idle("Demigrate");
|
|
}
|
|
|
|
/*
|
|
* Timer handler used to force CPU to start pushing its remaining RCU
|
|
* callbacks in the case where it entered dyntick-idle mode with callbacks
|
|
* pending. The hander doesn't really need to do anything because the
|
|
* real work is done upon re-entry to idle, or by the next scheduling-clock
|
|
* interrupt should idle not be re-entered.
|
|
*
|
|
* One special case: the timer gets migrated without awakening the CPU
|
|
* on which the timer was scheduled on. In this case, we must wake up
|
|
* that CPU. We do so with smp_call_function_single().
|
|
*/
|
|
static void rcu_idle_gp_timer_func(unsigned long cpu_in)
|
|
{
|
|
int cpu = (int)cpu_in;
|
|
|
|
trace_rcu_prep_idle("Timer");
|
|
if (cpu != smp_processor_id())
|
|
smp_call_function_single(cpu, rcu_idle_demigrate, NULL, 0);
|
|
else
|
|
WARN_ON_ONCE(1); /* Getting here can hang the system... */
|
|
}
|
|
|
|
/*
|
|
* Initialize the timer used to pull CPUs out of dyntick-idle mode.
|
|
*/
|
|
static void rcu_prepare_for_idle_init(int cpu)
|
|
{
|
|
struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
|
|
|
|
rdtp->dyntick_holdoff = jiffies - 1;
|
|
setup_timer(&rdtp->idle_gp_timer, rcu_idle_gp_timer_func, cpu);
|
|
rdtp->idle_gp_timer_expires = jiffies - 1;
|
|
rdtp->idle_first_pass = 1;
|
|
}
|
|
|
|
/*
|
|
* Clean up for exit from idle. Because we are exiting from idle, there
|
|
* is no longer any point to ->idle_gp_timer, so cancel it. This will
|
|
* do nothing if this timer is not active, so just cancel it unconditionally.
|
|
*/
|
|
static void rcu_cleanup_after_idle(int cpu)
|
|
{
|
|
struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
|
|
|
|
del_timer(&rdtp->idle_gp_timer);
|
|
trace_rcu_prep_idle("Cleanup after idle");
|
|
rdtp->tick_nohz_enabled_snap = ACCESS_ONCE(tick_nohz_enabled);
|
|
}
|
|
|
|
/*
|
|
* Check to see if any RCU-related work can be done by the current CPU,
|
|
* and if so, schedule a softirq to get it done. This function is part
|
|
* of the RCU implementation; it is -not- an exported member of the RCU API.
|
|
*
|
|
* The idea is for the current CPU to clear out all work required by the
|
|
* RCU core for the current grace period, so that this CPU can be permitted
|
|
* to enter dyntick-idle mode. In some cases, it will need to be awakened
|
|
* at the end of the grace period by whatever CPU ends the grace period.
|
|
* This allows CPUs to go dyntick-idle more quickly, and to reduce the
|
|
* number of wakeups by a modest integer factor.
|
|
*
|
|
* Because it is not legal to invoke rcu_process_callbacks() with irqs
|
|
* disabled, we do one pass of force_quiescent_state(), then do a
|
|
* invoke_rcu_core() to cause rcu_process_callbacks() to be invoked
|
|
* later. The ->dyntick_drain field controls the sequencing.
|
|
*
|
|
* The caller must have disabled interrupts.
|
|
*/
|
|
static void rcu_prepare_for_idle(int cpu)
|
|
{
|
|
struct timer_list *tp;
|
|
struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
|
|
int tne;
|
|
|
|
/* Handle nohz enablement switches conservatively. */
|
|
tne = ACCESS_ONCE(tick_nohz_enabled);
|
|
if (tne != rdtp->tick_nohz_enabled_snap) {
|
|
if (rcu_cpu_has_callbacks(cpu))
|
|
invoke_rcu_core(); /* force nohz to see update. */
|
|
rdtp->tick_nohz_enabled_snap = tne;
|
|
return;
|
|
}
|
|
if (!tne)
|
|
return;
|
|
|
|
/* Adaptive-tick mode, where usermode execution is idle to RCU. */
|
|
if (!is_idle_task(current)) {
|
|
rdtp->dyntick_holdoff = jiffies - 1;
|
|
if (rcu_cpu_has_nonlazy_callbacks(cpu)) {
|
|
trace_rcu_prep_idle("User dyntick with callbacks");
|
|
rdtp->idle_gp_timer_expires =
|
|
round_up(jiffies + RCU_IDLE_GP_DELAY,
|
|
RCU_IDLE_GP_DELAY);
|
|
} else if (rcu_cpu_has_callbacks(cpu)) {
|
|
rdtp->idle_gp_timer_expires =
|
|
round_jiffies(jiffies + RCU_IDLE_LAZY_GP_DELAY);
|
|
trace_rcu_prep_idle("User dyntick with lazy callbacks");
|
|
} else {
|
|
return;
|
|
}
|
|
tp = &rdtp->idle_gp_timer;
|
|
mod_timer_pinned(tp, rdtp->idle_gp_timer_expires);
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* If this is an idle re-entry, for example, due to use of
|
|
* RCU_NONIDLE() or the new idle-loop tracing API within the idle
|
|
* loop, then don't take any state-machine actions, unless the
|
|
* momentary exit from idle queued additional non-lazy callbacks.
|
|
* Instead, repost the ->idle_gp_timer if this CPU has callbacks
|
|
* pending.
|
|
*/
|
|
if (!rdtp->idle_first_pass &&
|
|
(rdtp->nonlazy_posted == rdtp->nonlazy_posted_snap)) {
|
|
if (rcu_cpu_has_callbacks(cpu)) {
|
|
tp = &rdtp->idle_gp_timer;
|
|
mod_timer_pinned(tp, rdtp->idle_gp_timer_expires);
|
|
}
|
|
return;
|
|
}
|
|
rdtp->idle_first_pass = 0;
|
|
rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted - 1;
|
|
|
|
/*
|
|
* If there are no callbacks on this CPU, enter dyntick-idle mode.
|
|
* Also reset state to avoid prejudicing later attempts.
|
|
*/
|
|
if (!rcu_cpu_has_callbacks(cpu)) {
|
|
rdtp->dyntick_holdoff = jiffies - 1;
|
|
rdtp->dyntick_drain = 0;
|
|
trace_rcu_prep_idle("No callbacks");
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* If in holdoff mode, just return. We will presumably have
|
|
* refrained from disabling the scheduling-clock tick.
|
|
*/
|
|
if (rdtp->dyntick_holdoff == jiffies) {
|
|
trace_rcu_prep_idle("In holdoff");
|
|
return;
|
|
}
|
|
|
|
/* Check and update the ->dyntick_drain sequencing. */
|
|
if (rdtp->dyntick_drain <= 0) {
|
|
/* First time through, initialize the counter. */
|
|
rdtp->dyntick_drain = RCU_IDLE_FLUSHES;
|
|
} else if (rdtp->dyntick_drain <= RCU_IDLE_OPT_FLUSHES &&
|
|
!rcu_pending(cpu) &&
|
|
!local_softirq_pending()) {
|
|
/* Can we go dyntick-idle despite still having callbacks? */
|
|
rdtp->dyntick_drain = 0;
|
|
rdtp->dyntick_holdoff = jiffies;
|
|
if (rcu_cpu_has_nonlazy_callbacks(cpu)) {
|
|
trace_rcu_prep_idle("Dyntick with callbacks");
|
|
rdtp->idle_gp_timer_expires =
|
|
round_up(jiffies + RCU_IDLE_GP_DELAY,
|
|
RCU_IDLE_GP_DELAY);
|
|
} else {
|
|
rdtp->idle_gp_timer_expires =
|
|
round_jiffies(jiffies + RCU_IDLE_LAZY_GP_DELAY);
|
|
trace_rcu_prep_idle("Dyntick with lazy callbacks");
|
|
}
|
|
tp = &rdtp->idle_gp_timer;
|
|
mod_timer_pinned(tp, rdtp->idle_gp_timer_expires);
|
|
rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
|
|
return; /* Nothing more to do immediately. */
|
|
} else if (--(rdtp->dyntick_drain) <= 0) {
|
|
/* We have hit the limit, so time to give up. */
|
|
rdtp->dyntick_holdoff = jiffies;
|
|
trace_rcu_prep_idle("Begin holdoff");
|
|
invoke_rcu_core(); /* Force the CPU out of dyntick-idle. */
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* Do one step of pushing the remaining RCU callbacks through
|
|
* the RCU core state machine.
|
|
*/
|
|
#ifdef CONFIG_TREE_PREEMPT_RCU
|
|
if (per_cpu(rcu_preempt_data, cpu).nxtlist) {
|
|
rcu_preempt_qs(cpu);
|
|
force_quiescent_state(&rcu_preempt_state);
|
|
}
|
|
#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
|
|
if (per_cpu(rcu_sched_data, cpu).nxtlist) {
|
|
rcu_sched_qs(cpu);
|
|
force_quiescent_state(&rcu_sched_state);
|
|
}
|
|
if (per_cpu(rcu_bh_data, cpu).nxtlist) {
|
|
rcu_bh_qs(cpu);
|
|
force_quiescent_state(&rcu_bh_state);
|
|
}
|
|
|
|
/*
|
|
* If RCU callbacks are still pending, RCU still needs this CPU.
|
|
* So try forcing the callbacks through the grace period.
|
|
*/
|
|
if (rcu_cpu_has_callbacks(cpu)) {
|
|
trace_rcu_prep_idle("More callbacks");
|
|
invoke_rcu_core();
|
|
} else {
|
|
trace_rcu_prep_idle("Callbacks drained");
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Keep a running count of the number of non-lazy callbacks posted
|
|
* on this CPU. This running counter (which is never decremented) allows
|
|
* rcu_prepare_for_idle() to detect when something out of the idle loop
|
|
* posts a callback, even if an equal number of callbacks are invoked.
|
|
* Of course, callbacks should only be posted from within a trace event
|
|
* designed to be called from idle or from within RCU_NONIDLE().
|
|
*/
|
|
static void rcu_idle_count_callbacks_posted(void)
|
|
{
|
|
__this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
|
|
}
|
|
|
|
/*
|
|
* Data for flushing lazy RCU callbacks at OOM time.
|
|
*/
|
|
static atomic_t oom_callback_count;
|
|
static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq);
|
|
|
|
/*
|
|
* RCU OOM callback -- decrement the outstanding count and deliver the
|
|
* wake-up if we are the last one.
|
|
*/
|
|
static void rcu_oom_callback(struct rcu_head *rhp)
|
|
{
|
|
if (atomic_dec_and_test(&oom_callback_count))
|
|
wake_up(&oom_callback_wq);
|
|
}
|
|
|
|
/*
|
|
* Post an rcu_oom_notify callback on the current CPU if it has at
|
|
* least one lazy callback. This will unnecessarily post callbacks
|
|
* to CPUs that already have a non-lazy callback at the end of their
|
|
* callback list, but this is an infrequent operation, so accept some
|
|
* extra overhead to keep things simple.
|
|
*/
|
|
static void rcu_oom_notify_cpu(void *unused)
|
|
{
|
|
struct rcu_state *rsp;
|
|
struct rcu_data *rdp;
|
|
|
|
for_each_rcu_flavor(rsp) {
|
|
rdp = __this_cpu_ptr(rsp->rda);
|
|
if (rdp->qlen_lazy != 0) {
|
|
atomic_inc(&oom_callback_count);
|
|
rsp->call(&rdp->oom_head, rcu_oom_callback);
|
|
}
|
|
}
|
|
}
|
|
|
|
/*
|
|
* If low on memory, ensure that each CPU has a non-lazy callback.
|
|
* This will wake up CPUs that have only lazy callbacks, in turn
|
|
* ensuring that they free up the corresponding memory in a timely manner.
|
|
* Because an uncertain amount of memory will be freed in some uncertain
|
|
* timeframe, we do not claim to have freed anything.
|
|
*/
|
|
static int rcu_oom_notify(struct notifier_block *self,
|
|
unsigned long notused, void *nfreed)
|
|
{
|
|
int cpu;
|
|
|
|
/* Wait for callbacks from earlier instance to complete. */
|
|
wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0);
|
|
|
|
/*
|
|
* Prevent premature wakeup: ensure that all increments happen
|
|
* before there is a chance of the counter reaching zero.
|
|
*/
|
|
atomic_set(&oom_callback_count, 1);
|
|
|
|
get_online_cpus();
|
|
for_each_online_cpu(cpu) {
|
|
smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
|
|
cond_resched();
|
|
}
|
|
put_online_cpus();
|
|
|
|
/* Unconditionally decrement: no need to wake ourselves up. */
|
|
atomic_dec(&oom_callback_count);
|
|
|
|
return NOTIFY_OK;
|
|
}
|
|
|
|
static struct notifier_block rcu_oom_nb = {
|
|
.notifier_call = rcu_oom_notify
|
|
};
|
|
|
|
static int __init rcu_register_oom_notifier(void)
|
|
{
|
|
register_oom_notifier(&rcu_oom_nb);
|
|
return 0;
|
|
}
|
|
early_initcall(rcu_register_oom_notifier);
|
|
|
|
#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
|
|
|
|
#ifdef CONFIG_RCU_CPU_STALL_INFO
|
|
|
|
#ifdef CONFIG_RCU_FAST_NO_HZ
|
|
|
|
static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
|
|
{
|
|
struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
|
|
struct timer_list *tltp = &rdtp->idle_gp_timer;
|
|
char c;
|
|
|
|
c = rdtp->dyntick_holdoff == jiffies ? 'H' : '.';
|
|
if (timer_pending(tltp))
|
|
sprintf(cp, "drain=%d %c timer=%lu",
|
|
rdtp->dyntick_drain, c, tltp->expires - jiffies);
|
|
else
|
|
sprintf(cp, "drain=%d %c timer not pending",
|
|
rdtp->dyntick_drain, c);
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
|
|
|
|
static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
|
|
{
|
|
*cp = '\0';
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
|
|
|
|
/* Initiate the stall-info list. */
|
|
static void print_cpu_stall_info_begin(void)
|
|
{
|
|
printk(KERN_CONT "\n");
|
|
}
|
|
|
|
/*
|
|
* Print out diagnostic information for the specified stalled CPU.
|
|
*
|
|
* If the specified CPU is aware of the current RCU grace period
|
|
* (flavor specified by rsp), then print the number of scheduling
|
|
* clock interrupts the CPU has taken during the time that it has
|
|
* been aware. Otherwise, print the number of RCU grace periods
|
|
* that this CPU is ignorant of, for example, "1" if the CPU was
|
|
* aware of the previous grace period.
|
|
*
|
|
* Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
|
|
*/
|
|
static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
|
|
{
|
|
char fast_no_hz[72];
|
|
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
|
|
struct rcu_dynticks *rdtp = rdp->dynticks;
|
|
char *ticks_title;
|
|
unsigned long ticks_value;
|
|
|
|
if (rsp->gpnum == rdp->gpnum) {
|
|
ticks_title = "ticks this GP";
|
|
ticks_value = rdp->ticks_this_gp;
|
|
} else {
|
|
ticks_title = "GPs behind";
|
|
ticks_value = rsp->gpnum - rdp->gpnum;
|
|
}
|
|
print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
|
|
printk(KERN_ERR "\t%d: (%lu %s) idle=%03x/%llx/%d %s\n",
|
|
cpu, ticks_value, ticks_title,
|
|
atomic_read(&rdtp->dynticks) & 0xfff,
|
|
rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
|
|
fast_no_hz);
|
|
}
|
|
|
|
/* Terminate the stall-info list. */
|
|
static void print_cpu_stall_info_end(void)
|
|
{
|
|
printk(KERN_ERR "\t");
|
|
}
|
|
|
|
/* Zero ->ticks_this_gp for all flavors of RCU. */
|
|
static void zero_cpu_stall_ticks(struct rcu_data *rdp)
|
|
{
|
|
rdp->ticks_this_gp = 0;
|
|
}
|
|
|
|
/* Increment ->ticks_this_gp for all flavors of RCU. */
|
|
static void increment_cpu_stall_ticks(void)
|
|
{
|
|
struct rcu_state *rsp;
|
|
|
|
for_each_rcu_flavor(rsp)
|
|
__this_cpu_ptr(rsp->rda)->ticks_this_gp++;
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
|
|
|
|
static void print_cpu_stall_info_begin(void)
|
|
{
|
|
printk(KERN_CONT " {");
|
|
}
|
|
|
|
static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
|
|
{
|
|
printk(KERN_CONT " %d", cpu);
|
|
}
|
|
|
|
static void print_cpu_stall_info_end(void)
|
|
{
|
|
printk(KERN_CONT "} ");
|
|
}
|
|
|
|
static void zero_cpu_stall_ticks(struct rcu_data *rdp)
|
|
{
|
|
}
|
|
|
|
static void increment_cpu_stall_ticks(void)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
|
|
|
|
#ifdef CONFIG_RCU_NOCB_CPU
|
|
|
|
/*
|
|
* Offload callback processing from the boot-time-specified set of CPUs
|
|
* specified by rcu_nocb_mask. For each CPU in the set, there is a
|
|
* kthread created that pulls the callbacks from the corresponding CPU,
|
|
* waits for a grace period to elapse, and invokes the callbacks.
|
|
* The no-CBs CPUs do a wake_up() on their kthread when they insert
|
|
* a callback into any empty list, unless the rcu_nocb_poll boot parameter
|
|
* has been specified, in which case each kthread actively polls its
|
|
* CPU. (Which isn't so great for energy efficiency, but which does
|
|
* reduce RCU's overhead on that CPU.)
|
|
*
|
|
* This is intended to be used in conjunction with Frederic Weisbecker's
|
|
* adaptive-idle work, which would seriously reduce OS jitter on CPUs
|
|
* running CPU-bound user-mode computations.
|
|
*
|
|
* Offloading of callback processing could also in theory be used as
|
|
* an energy-efficiency measure because CPUs with no RCU callbacks
|
|
* queued are more aggressive about entering dyntick-idle mode.
|
|
*/
|
|
|
|
|
|
/* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
|
|
static int __init rcu_nocb_setup(char *str)
|
|
{
|
|
alloc_bootmem_cpumask_var(&rcu_nocb_mask);
|
|
have_rcu_nocb_mask = true;
|
|
cpulist_parse(str, rcu_nocb_mask);
|
|
return 1;
|
|
}
|
|
__setup("rcu_nocbs=", rcu_nocb_setup);
|
|
|
|
static int __init parse_rcu_nocb_poll(char *arg)
|
|
{
|
|
rcu_nocb_poll = 1;
|
|
return 0;
|
|
}
|
|
early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
|
|
|
|
/* Is the specified CPU a no-CPUs CPU? */
|
|
static bool is_nocb_cpu(int cpu)
|
|
{
|
|
if (have_rcu_nocb_mask)
|
|
return cpumask_test_cpu(cpu, rcu_nocb_mask);
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* Enqueue the specified string of rcu_head structures onto the specified
|
|
* CPU's no-CBs lists. The CPU is specified by rdp, the head of the
|
|
* string by rhp, and the tail of the string by rhtp. The non-lazy/lazy
|
|
* counts are supplied by rhcount and rhcount_lazy.
|
|
*
|
|
* If warranted, also wake up the kthread servicing this CPUs queues.
|
|
*/
|
|
static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
|
|
struct rcu_head *rhp,
|
|
struct rcu_head **rhtp,
|
|
int rhcount, int rhcount_lazy)
|
|
{
|
|
int len;
|
|
struct rcu_head **old_rhpp;
|
|
struct task_struct *t;
|
|
|
|
/* Enqueue the callback on the nocb list and update counts. */
|
|
old_rhpp = xchg(&rdp->nocb_tail, rhtp);
|
|
ACCESS_ONCE(*old_rhpp) = rhp;
|
|
atomic_long_add(rhcount, &rdp->nocb_q_count);
|
|
atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy);
|
|
|
|
/* If we are not being polled and there is a kthread, awaken it ... */
|
|
t = ACCESS_ONCE(rdp->nocb_kthread);
|
|
if (rcu_nocb_poll | !t)
|
|
return;
|
|
len = atomic_long_read(&rdp->nocb_q_count);
|
|
if (old_rhpp == &rdp->nocb_head) {
|
|
wake_up(&rdp->nocb_wq); /* ... only if queue was empty ... */
|
|
rdp->qlen_last_fqs_check = 0;
|
|
} else if (len > rdp->qlen_last_fqs_check + qhimark) {
|
|
wake_up_process(t); /* ... or if many callbacks queued. */
|
|
rdp->qlen_last_fqs_check = LONG_MAX / 2;
|
|
}
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* This is a helper for __call_rcu(), which invokes this when the normal
|
|
* callback queue is inoperable. If this is not a no-CBs CPU, this
|
|
* function returns failure back to __call_rcu(), which can complain
|
|
* appropriately.
|
|
*
|
|
* Otherwise, this function queues the callback where the corresponding
|
|
* "rcuo" kthread can find it.
|
|
*/
|
|
static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
|
|
bool lazy)
|
|
{
|
|
|
|
if (!is_nocb_cpu(rdp->cpu))
|
|
return 0;
|
|
__call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy);
|
|
return 1;
|
|
}
|
|
|
|
/*
|
|
* Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
|
|
* not a no-CBs CPU.
|
|
*/
|
|
static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
|
|
struct rcu_data *rdp)
|
|
{
|
|
long ql = rsp->qlen;
|
|
long qll = rsp->qlen_lazy;
|
|
|
|
/* If this is not a no-CBs CPU, tell the caller to do it the old way. */
|
|
if (!is_nocb_cpu(smp_processor_id()))
|
|
return 0;
|
|
rsp->qlen = 0;
|
|
rsp->qlen_lazy = 0;
|
|
|
|
/* First, enqueue the donelist, if any. This preserves CB ordering. */
|
|
if (rsp->orphan_donelist != NULL) {
|
|
__call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist,
|
|
rsp->orphan_donetail, ql, qll);
|
|
ql = qll = 0;
|
|
rsp->orphan_donelist = NULL;
|
|
rsp->orphan_donetail = &rsp->orphan_donelist;
|
|
}
|
|
if (rsp->orphan_nxtlist != NULL) {
|
|
__call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist,
|
|
rsp->orphan_nxttail, ql, qll);
|
|
ql = qll = 0;
|
|
rsp->orphan_nxtlist = NULL;
|
|
rsp->orphan_nxttail = &rsp->orphan_nxtlist;
|
|
}
|
|
return 1;
|
|
}
|
|
|
|
/*
|
|
* There must be at least one non-no-CBs CPU in operation at any given
|
|
* time, because no-CBs CPUs are not capable of initiating grace periods
|
|
* independently. This function therefore complains if the specified
|
|
* CPU is the last non-no-CBs CPU, allowing the CPU-hotplug system to
|
|
* avoid offlining the last such CPU. (Recursion is a wonderful thing,
|
|
* but you have to have a base case!)
|
|
*/
|
|
static bool nocb_cpu_expendable(int cpu)
|
|
{
|
|
cpumask_var_t non_nocb_cpus;
|
|
int ret;
|
|
|
|
/*
|
|
* If there are no no-CB CPUs or if this CPU is not a no-CB CPU,
|
|
* then offlining this CPU is harmless. Let it happen.
|
|
*/
|
|
if (!have_rcu_nocb_mask || is_nocb_cpu(cpu))
|
|
return 1;
|
|
|
|
/* If no memory, play it safe and keep the CPU around. */
|
|
if (!alloc_cpumask_var(&non_nocb_cpus, GFP_NOIO))
|
|
return 0;
|
|
cpumask_andnot(non_nocb_cpus, cpu_online_mask, rcu_nocb_mask);
|
|
cpumask_clear_cpu(cpu, non_nocb_cpus);
|
|
ret = !cpumask_empty(non_nocb_cpus);
|
|
free_cpumask_var(non_nocb_cpus);
|
|
return ret;
|
|
}
|
|
|
|
/*
|
|
* Helper structure for remote registry of RCU callbacks.
|
|
* This is needed for when a no-CBs CPU needs to start a grace period.
|
|
* If it just invokes call_rcu(), the resulting callback will be queued,
|
|
* which can result in deadlock.
|
|
*/
|
|
struct rcu_head_remote {
|
|
struct rcu_head *rhp;
|
|
call_rcu_func_t *crf;
|
|
void (*func)(struct rcu_head *rhp);
|
|
};
|
|
|
|
/*
|
|
* Register a callback as specified by the rcu_head_remote struct.
|
|
* This function is intended to be invoked via smp_call_function_single().
|
|
*/
|
|
static void call_rcu_local(void *arg)
|
|
{
|
|
struct rcu_head_remote *rhrp =
|
|
container_of(arg, struct rcu_head_remote, rhp);
|
|
|
|
rhrp->crf(rhrp->rhp, rhrp->func);
|
|
}
|
|
|
|
/*
|
|
* Set up an rcu_head_remote structure and the invoke call_rcu_local()
|
|
* on CPU 0 (which is guaranteed to be a non-no-CBs CPU) via
|
|
* smp_call_function_single().
|
|
*/
|
|
static void invoke_crf_remote(struct rcu_head *rhp,
|
|
void (*func)(struct rcu_head *rhp),
|
|
call_rcu_func_t crf)
|
|
{
|
|
struct rcu_head_remote rhr;
|
|
|
|
rhr.rhp = rhp;
|
|
rhr.crf = crf;
|
|
rhr.func = func;
|
|
smp_call_function_single(0, call_rcu_local, &rhr, 1);
|
|
}
|
|
|
|
/*
|
|
* Helper functions to be passed to wait_rcu_gp(), each of which
|
|
* invokes invoke_crf_remote() to register a callback appropriately.
|
|
*/
|
|
static void __maybe_unused
|
|
call_rcu_preempt_remote(struct rcu_head *rhp,
|
|
void (*func)(struct rcu_head *rhp))
|
|
{
|
|
invoke_crf_remote(rhp, func, call_rcu);
|
|
}
|
|
static void call_rcu_bh_remote(struct rcu_head *rhp,
|
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void (*func)(struct rcu_head *rhp))
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{
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invoke_crf_remote(rhp, func, call_rcu_bh);
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}
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static void call_rcu_sched_remote(struct rcu_head *rhp,
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void (*func)(struct rcu_head *rhp))
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{
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invoke_crf_remote(rhp, func, call_rcu_sched);
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}
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|
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/*
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* Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes
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* callbacks queued by the corresponding no-CBs CPU.
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*/
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static int rcu_nocb_kthread(void *arg)
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{
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int c, cl;
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struct rcu_head *list;
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struct rcu_head *next;
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struct rcu_head **tail;
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struct rcu_data *rdp = arg;
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|
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/* Each pass through this loop invokes one batch of callbacks */
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for (;;) {
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/* If not polling, wait for next batch of callbacks. */
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if (!rcu_nocb_poll)
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wait_event_interruptible(rdp->nocb_wq, rdp->nocb_head);
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list = ACCESS_ONCE(rdp->nocb_head);
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if (!list) {
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schedule_timeout_interruptible(1);
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flush_signals(current);
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continue;
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}
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|
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/*
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* Extract queued callbacks, update counts, and wait
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* for a grace period to elapse.
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*/
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ACCESS_ONCE(rdp->nocb_head) = NULL;
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tail = xchg(&rdp->nocb_tail, &rdp->nocb_head);
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c = atomic_long_xchg(&rdp->nocb_q_count, 0);
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cl = atomic_long_xchg(&rdp->nocb_q_count_lazy, 0);
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ACCESS_ONCE(rdp->nocb_p_count) += c;
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ACCESS_ONCE(rdp->nocb_p_count_lazy) += cl;
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wait_rcu_gp(rdp->rsp->call_remote);
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|
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/* Each pass through the following loop invokes a callback. */
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trace_rcu_batch_start(rdp->rsp->name, cl, c, -1);
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c = cl = 0;
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while (list) {
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next = list->next;
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/* Wait for enqueuing to complete, if needed. */
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|
while (next == NULL && &list->next != tail) {
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|
schedule_timeout_interruptible(1);
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|
next = list->next;
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|
}
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|
debug_rcu_head_unqueue(list);
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|
local_bh_disable();
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|
if (__rcu_reclaim(rdp->rsp->name, list))
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|
cl++;
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|
c++;
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|
local_bh_enable();
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|
list = next;
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|
}
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|
trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
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|
ACCESS_ONCE(rdp->nocb_p_count) -= c;
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|
ACCESS_ONCE(rdp->nocb_p_count_lazy) -= cl;
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|
rdp->n_nocbs_invoked += c;
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|
}
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|
return 0;
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|
}
|
|
|
|
/* Initialize per-rcu_data variables for no-CBs CPUs. */
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|
static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
|
|
{
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|
rdp->nocb_tail = &rdp->nocb_head;
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|
init_waitqueue_head(&rdp->nocb_wq);
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|
}
|
|
|
|
/* Create a kthread for each RCU flavor for each no-CBs CPU. */
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|
static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
|
|
{
|
|
int cpu;
|
|
struct rcu_data *rdp;
|
|
struct task_struct *t;
|
|
|
|
if (rcu_nocb_mask == NULL)
|
|
return;
|
|
for_each_cpu(cpu, rcu_nocb_mask) {
|
|
rdp = per_cpu_ptr(rsp->rda, cpu);
|
|
t = kthread_run(rcu_nocb_kthread, rdp, "rcuo%d", cpu);
|
|
BUG_ON(IS_ERR(t));
|
|
ACCESS_ONCE(rdp->nocb_kthread) = t;
|
|
}
|
|
}
|
|
|
|
/* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
|
|
static void init_nocb_callback_list(struct rcu_data *rdp)
|
|
{
|
|
if (rcu_nocb_mask == NULL ||
|
|
!cpumask_test_cpu(rdp->cpu, rcu_nocb_mask))
|
|
return;
|
|
rdp->nxttail[RCU_NEXT_TAIL] = NULL;
|
|
}
|
|
|
|
/* Initialize the ->call_remote fields in the rcu_state structures. */
|
|
static void __init rcu_init_nocb(void)
|
|
{
|
|
#ifdef CONFIG_PREEMPT_RCU
|
|
rcu_preempt_state.call_remote = call_rcu_preempt_remote;
|
|
#endif /* #ifdef CONFIG_PREEMPT_RCU */
|
|
rcu_bh_state.call_remote = call_rcu_bh_remote;
|
|
rcu_sched_state.call_remote = call_rcu_sched_remote;
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_RCU_NOCB_CPU */
|
|
|
|
static bool is_nocb_cpu(int cpu)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
|
|
bool lazy)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
|
|
struct rcu_data *rdp)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
static bool nocb_cpu_expendable(int cpu)
|
|
{
|
|
return 1;
|
|
}
|
|
|
|
static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
|
|
{
|
|
}
|
|
|
|
static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
|
|
{
|
|
}
|
|
|
|
static void init_nocb_callback_list(struct rcu_data *rdp)
|
|
{
|
|
}
|
|
|
|
static void __init rcu_init_nocb(void)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
|