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rcu_tasks: Convert bespoke callback list to rcu_segcblist structure 

This commit moves from a bespoke head and tail pointer in the
rcu_tasks_percpu structure to an rcu_segcblist structure, thus allowing
associating the grace-period sequence number with groups of callbacks.
This in turn will allow callbacks to be invoked independently on
different CPUs.

Reported-by: Martin Lau <kafai@fb.com>
Cc: Neeraj Upadhyay <neeraj.iitr10@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2021-11-08 16:18:57 -08:00
parent b14fb4fbbc
commit 9b073de1c7
2 changed files with 30 additions and 24 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
kernel/rcu/Kconfig
View File

@ -112,7 +112,7 @@ config RCU_STALL_COMMON
making these warnings mandatory for the tree variants.
config RCU_NEED_SEGCBLIST
def_bool ( TREE_RCU || TREE_SRCU )
def_bool ( TREE_RCU || TREE_SRCU || TASKS_RCU_GENERIC )
config RCU_FANOUT
int "Tree-based hierarchical RCU fanout value"

52
kernel/rcu/tasks.h
View File

@ -6,6 +6,7 @@
*/
#ifdef CONFIG_TASKS_RCU_GENERIC
#include "rcu_segcblist.h"
////////////////////////////////////////////////////////////////////////
//
@ -21,13 +22,11 @@ typedef void (*postgp_func_t)(struct rcu_tasks *rtp);
/**
* struct rcu_tasks_percpu - Per-CPU component of definition for a Tasks-RCU-like mechanism.
* @cbs_head: Head of callback list.
* @cbs_tail: Tail pointer for callback list.
* @cblist: Callback list.
* @cbs_pcpu_lock: Lock protecting per-CPU callback list.
*/
struct rcu_tasks_percpu {
struct rcu_head *cbs_head;
struct rcu_head **cbs_tail;
struct rcu_segcblist cblist;
raw_spinlock_t cbs_pcpu_lock;
};
@ -180,8 +179,8 @@ static void cblist_init_generic(struct rcu_tasks *rtp)
if (cpu)
raw_spin_lock_init(&rtpcp->cbs_pcpu_lock);
raw_spin_lock(&rtpcp->cbs_pcpu_lock); // irqs already disabled.
if (!WARN_ON_ONCE(rtpcp->cbs_tail))
rtpcp->cbs_tail = &rtpcp->cbs_head;
if (rcu_segcblist_empty(&rtpcp->cblist))
rcu_segcblist_init(&rtpcp->cblist);
raw_spin_unlock(&rtpcp->cbs_pcpu_lock); // irqs remain disabled.
}
raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags);
@ -202,14 +201,13 @@ static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
rtpcp = per_cpu_ptr(rtp->rtpcpu,
smp_processor_id() >> READ_ONCE(rtp->percpu_enqueue_shift));
raw_spin_lock(&rtpcp->cbs_pcpu_lock);
if (!rtpcp->cbs_tail) {
if (!rcu_segcblist_is_enabled(&rtpcp->cblist)) {
raw_spin_unlock(&rtpcp->cbs_pcpu_lock); // irqs remain disabled.
cblist_init_generic(rtp);
raw_spin_lock(&rtpcp->cbs_pcpu_lock); // irqs already disabled.
}
needwake = !rtpcp->cbs_head;
WRITE_ONCE(*rtpcp->cbs_tail, rhp);
rtpcp->cbs_tail = &rhp->next;
needwake = rcu_segcblist_empty(&rtpcp->cblist);
rcu_segcblist_enqueue(&rtpcp->cblist, rhp);
raw_spin_unlock_irqrestore(&rtpcp->cbs_pcpu_lock, flags);
/* We can't create the thread unless interrupts are enabled. */
if (needwake && READ_ONCE(rtp->kthread_ptr))
@ -231,8 +229,9 @@ static void synchronize_rcu_tasks_generic(struct rcu_tasks *rtp)
static int __noreturn rcu_tasks_kthread(void *arg)
{
unsigned long flags;
struct rcu_head *list;
struct rcu_head *next;
int len;
struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl);
struct rcu_head *rhp;
struct rcu_tasks *rtp = arg;
/* Run on housekeeping CPUs by default. Sysadm can move if desired. */
@ -253,16 +252,15 @@ static int __noreturn rcu_tasks_kthread(void *arg)
/* Pick up any new callbacks. */
raw_spin_lock_irqsave(&rtpcp->cbs_pcpu_lock, flags);
smp_mb__after_spinlock(); // Order updates vs. GP.
list = rtpcp->cbs_head;
rtpcp->cbs_head = NULL;
rtpcp->cbs_tail = &rtpcp->cbs_head;
rcu_segcblist_advance(&rtpcp->cblist, rcu_seq_current(&rtp->tasks_gp_seq));
(void)rcu_segcblist_accelerate(&rtpcp->cblist, rcu_seq_snap(&rtp->tasks_gp_seq));
raw_spin_unlock_irqrestore(&rtpcp->cbs_pcpu_lock, flags);
/* If there were none, wait a bit and start over. */
if (!list) {
if (!rcu_segcblist_pend_cbs(&rtpcp->cblist)) {
wait_event_interruptible(rtp->cbs_wq,
READ_ONCE(rtpcp->cbs_head));
if (!rtpcp->cbs_head) {
rcu_segcblist_pend_cbs(&rtpcp->cblist));
if (!rcu_segcblist_pend_cbs(&rtpcp->cblist)) {
WARN_ON(signal_pending(current));
set_tasks_gp_state(rtp, RTGS_WAIT_WAIT_CBS);
schedule_timeout_idle(HZ/10);
@ -279,14 +277,22 @@ static int __noreturn rcu_tasks_kthread(void *arg)
/* Invoke the callbacks. */
set_tasks_gp_state(rtp, RTGS_INVOKE_CBS);
while (list) {
next = list->next;
raw_spin_lock_irqsave(&rtpcp->cbs_pcpu_lock, flags);
smp_mb__after_spinlock(); // Order updates vs. GP.
rcu_segcblist_advance(&rtpcp->cblist, rcu_seq_current(&rtp->tasks_gp_seq));
rcu_segcblist_extract_done_cbs(&rtpcp->cblist, &rcl);
raw_spin_unlock_irqrestore(&rtpcp->cbs_pcpu_lock, flags);
len = rcl.len;
for (rhp = rcu_cblist_dequeue(&rcl); rhp; rhp = rcu_cblist_dequeue(&rcl)) {
local_bh_disable();
list->func(list);
rhp->func(rhp);
local_bh_enable();
list = next;
cond_resched();
}
raw_spin_lock_irqsave(&rtpcp->cbs_pcpu_lock, flags);
rcu_segcblist_add_len(&rtpcp->cblist, -len);
(void)rcu_segcblist_accelerate(&rtpcp->cblist, rcu_seq_snap(&rtp->tasks_gp_seq));
raw_spin_unlock_irqrestore(&rtpcp->cbs_pcpu_lock, flags);
/* Paranoid sleep to keep this from entering a tight loop */
schedule_timeout_idle(rtp->gp_sleep);
}
@ -339,7 +345,7 @@ static void show_rcu_tasks_generic_gp_kthread(struct rcu_tasks *rtp, char *s)
data_race(rcu_seq_current(&rtp->tasks_gp_seq)),
data_race(rtp->n_ipis_fails), data_race(rtp->n_ipis),
".k"[!!data_race(rtp->kthread_ptr)],
".C"[!!data_race(rtpcp->cbs_head)],
".C"[!data_race(rcu_segcblist_empty(&rtpcp->cblist))],
s);
}
#endif // #ifndef CONFIG_TINY_RCU