438 lines
14 KiB
C
438 lines
14 KiB
C
/*
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* Read-Copy Update mechanism for mutual exclusion
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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 IBM Corporation, 2001
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*
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* Author: Dipankar Sarma <dipankar@in.ibm.com>
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*
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* Based on the original work by Paul McKenney <paulmck@us.ibm.com>
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* and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
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* Papers:
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* http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
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* http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
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*
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* For detailed explanation of Read-Copy Update mechanism see -
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* http://lse.sourceforge.net/locking/rcupdate.html
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*
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*/
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#ifndef __LINUX_RCUPDATE_H
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#define __LINUX_RCUPDATE_H
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#include <linux/cache.h>
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#include <linux/spinlock.h>
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#include <linux/threads.h>
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#include <linux/cpumask.h>
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#include <linux/seqlock.h>
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#include <linux/lockdep.h>
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#include <linux/completion.h>
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/**
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* struct rcu_head - callback structure for use with RCU
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* @next: next update requests in a list
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* @func: actual update function to call after the grace period.
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*/
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struct rcu_head {
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struct rcu_head *next;
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void (*func)(struct rcu_head *head);
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};
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/* Exported common interfaces */
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extern void synchronize_rcu_bh(void);
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extern void synchronize_sched(void);
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extern void rcu_barrier(void);
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extern void rcu_barrier_bh(void);
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extern void rcu_barrier_sched(void);
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extern void synchronize_sched_expedited(void);
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extern int sched_expedited_torture_stats(char *page);
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/* Internal to kernel */
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extern void rcu_init(void);
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extern int rcu_scheduler_active;
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extern void rcu_scheduler_starting(void);
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#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
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#include <linux/rcutree.h>
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#elif defined(CONFIG_TINY_RCU)
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#include <linux/rcutiny.h>
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#else
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#error "Unknown RCU implementation specified to kernel configuration"
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#endif
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#define RCU_HEAD_INIT { .next = NULL, .func = NULL }
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#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
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#define INIT_RCU_HEAD(ptr) do { \
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(ptr)->next = NULL; (ptr)->func = NULL; \
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} while (0)
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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extern struct lockdep_map rcu_lock_map;
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# define rcu_read_acquire() \
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lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
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# define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_)
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extern struct lockdep_map rcu_bh_lock_map;
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# define rcu_read_acquire_bh() \
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lock_acquire(&rcu_bh_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
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# define rcu_read_release_bh() lock_release(&rcu_bh_lock_map, 1, _THIS_IP_)
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extern struct lockdep_map rcu_sched_lock_map;
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# define rcu_read_acquire_sched() \
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lock_acquire(&rcu_sched_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
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# define rcu_read_release_sched() \
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lock_release(&rcu_sched_lock_map, 1, _THIS_IP_)
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/**
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* rcu_read_lock_held - might we be in RCU read-side critical section?
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*
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* If CONFIG_PROVE_LOCKING is selected and enabled, returns nonzero iff in
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* an RCU read-side critical section. In absence of CONFIG_PROVE_LOCKING,
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* this assumes we are in an RCU read-side critical section unless it can
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* prove otherwise.
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*/
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static inline int rcu_read_lock_held(void)
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{
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if (debug_locks)
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return lock_is_held(&rcu_lock_map);
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return 1;
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}
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/**
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* rcu_read_lock_bh_held - might we be in RCU-bh read-side critical section?
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*
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* If CONFIG_PROVE_LOCKING is selected and enabled, returns nonzero iff in
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* an RCU-bh read-side critical section. In absence of CONFIG_PROVE_LOCKING,
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* this assumes we are in an RCU-bh read-side critical section unless it can
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* prove otherwise.
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*/
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static inline int rcu_read_lock_bh_held(void)
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{
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if (debug_locks)
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return lock_is_held(&rcu_bh_lock_map);
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return 1;
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}
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/**
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* rcu_read_lock_sched_held - might we be in RCU-sched read-side critical section?
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*
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* If CONFIG_PROVE_LOCKING is selected and enabled, returns nonzero iff in an
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* RCU-sched read-side critical section. In absence of CONFIG_PROVE_LOCKING,
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* this assumes we are in an RCU-sched read-side critical section unless it
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* can prove otherwise. Note that disabling of preemption (including
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* disabling irqs) counts as an RCU-sched read-side critical section.
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*/
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static inline int rcu_read_lock_sched_held(void)
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{
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int lockdep_opinion = 0;
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if (debug_locks)
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lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
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return lockdep_opinion || preempt_count() != 0 || !rcu_scheduler_active;
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}
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#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
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# define rcu_read_acquire() do { } while (0)
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# define rcu_read_release() do { } while (0)
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# define rcu_read_acquire_bh() do { } while (0)
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# define rcu_read_release_bh() do { } while (0)
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# define rcu_read_acquire_sched() do { } while (0)
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# define rcu_read_release_sched() do { } while (0)
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static inline int rcu_read_lock_held(void)
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{
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return 1;
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}
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static inline int rcu_read_lock_bh_held(void)
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{
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return 1;
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}
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static inline int rcu_read_lock_sched_held(void)
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{
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return preempt_count() != 0 || !rcu_scheduler_active;
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}
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#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
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#ifdef CONFIG_PROVE_RCU
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/**
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* rcu_dereference_check - rcu_dereference with debug checking
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*
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* Do an rcu_dereference(), but check that the context is correct.
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* For example, rcu_dereference_check(gp, rcu_read_lock_held()) to
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* ensure that the rcu_dereference_check() executes within an RCU
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* read-side critical section. It is also possible to check for
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* locks being held, for example, by using lockdep_is_held().
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*/
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#define rcu_dereference_check(p, c) \
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({ \
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if (debug_locks && !(c)) \
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lockdep_rcu_dereference(__FILE__, __LINE__); \
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rcu_dereference_raw(p); \
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})
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#else /* #ifdef CONFIG_PROVE_RCU */
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#define rcu_dereference_check(p, c) rcu_dereference_raw(p)
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#endif /* #else #ifdef CONFIG_PROVE_RCU */
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/**
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* rcu_read_lock - mark the beginning of an RCU read-side critical section.
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*
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* When synchronize_rcu() is invoked on one CPU while other CPUs
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* are within RCU read-side critical sections, then the
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* synchronize_rcu() is guaranteed to block until after all the other
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* CPUs exit their critical sections. Similarly, if call_rcu() is invoked
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* on one CPU while other CPUs are within RCU read-side critical
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* sections, invocation of the corresponding RCU callback is deferred
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* until after the all the other CPUs exit their critical sections.
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*
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* Note, however, that RCU callbacks are permitted to run concurrently
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* with RCU read-side critical sections. One way that this can happen
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* is via the following sequence of events: (1) CPU 0 enters an RCU
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* read-side critical section, (2) CPU 1 invokes call_rcu() to register
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* an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
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* (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
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* callback is invoked. This is legal, because the RCU read-side critical
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* section that was running concurrently with the call_rcu() (and which
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* therefore might be referencing something that the corresponding RCU
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* callback would free up) has completed before the corresponding
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* RCU callback is invoked.
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*
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* RCU read-side critical sections may be nested. Any deferred actions
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* will be deferred until the outermost RCU read-side critical section
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* completes.
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*
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* It is illegal to block while in an RCU read-side critical section.
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*/
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static inline void rcu_read_lock(void)
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{
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__rcu_read_lock();
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__acquire(RCU);
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rcu_read_acquire();
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}
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/*
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* So where is rcu_write_lock()? It does not exist, as there is no
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* way for writers to lock out RCU readers. This is a feature, not
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* a bug -- this property is what provides RCU's performance benefits.
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* Of course, writers must coordinate with each other. The normal
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* spinlock primitives work well for this, but any other technique may be
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* used as well. RCU does not care how the writers keep out of each
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* others' way, as long as they do so.
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*/
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/**
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* rcu_read_unlock - marks the end of an RCU read-side critical section.
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*
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* See rcu_read_lock() for more information.
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*/
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static inline void rcu_read_unlock(void)
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{
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rcu_read_release();
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__release(RCU);
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__rcu_read_unlock();
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}
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/**
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* rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
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*
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* This is equivalent of rcu_read_lock(), but to be used when updates
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* are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
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* consider completion of a softirq handler to be a quiescent state,
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* a process in RCU read-side critical section must be protected by
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* disabling softirqs. Read-side critical sections in interrupt context
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* can use just rcu_read_lock().
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*
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*/
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static inline void rcu_read_lock_bh(void)
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{
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__rcu_read_lock_bh();
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__acquire(RCU_BH);
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rcu_read_acquire_bh();
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}
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/*
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* rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
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*
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* See rcu_read_lock_bh() for more information.
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*/
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static inline void rcu_read_unlock_bh(void)
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{
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rcu_read_release_bh();
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__release(RCU_BH);
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__rcu_read_unlock_bh();
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}
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/**
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* rcu_read_lock_sched - mark the beginning of a RCU-classic critical section
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*
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* Should be used with either
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* - synchronize_sched()
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* or
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* - call_rcu_sched() and rcu_barrier_sched()
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* on the write-side to insure proper synchronization.
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*/
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static inline void rcu_read_lock_sched(void)
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{
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preempt_disable();
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__acquire(RCU_SCHED);
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rcu_read_acquire_sched();
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}
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/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
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static inline notrace void rcu_read_lock_sched_notrace(void)
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{
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preempt_disable_notrace();
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__acquire(RCU_SCHED);
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}
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/*
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* rcu_read_unlock_sched - marks the end of a RCU-classic critical section
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*
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* See rcu_read_lock_sched for more information.
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*/
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static inline void rcu_read_unlock_sched(void)
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{
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rcu_read_release_sched();
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__release(RCU_SCHED);
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preempt_enable();
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}
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/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
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static inline notrace void rcu_read_unlock_sched_notrace(void)
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{
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__release(RCU_SCHED);
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preempt_enable_notrace();
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}
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/**
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* rcu_dereference_raw - fetch an RCU-protected pointer
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*
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* The caller must be within some flavor of RCU read-side critical
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* section, or must be otherwise preventing the pointer from changing,
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* for example, by holding an appropriate lock. This pointer may later
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* be safely dereferenced. It is the caller's responsibility to have
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* done the right thing, as this primitive does no checking of any kind.
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*
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* Inserts memory barriers on architectures that require them
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* (currently only the Alpha), and, more importantly, documents
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* exactly which pointers are protected by RCU.
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*/
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#define rcu_dereference_raw(p) ({ \
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typeof(p) _________p1 = ACCESS_ONCE(p); \
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smp_read_barrier_depends(); \
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(_________p1); \
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})
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/**
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* rcu_dereference - fetch an RCU-protected pointer, checking for RCU
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*
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* Makes rcu_dereference_check() do the dirty work.
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*/
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#define rcu_dereference(p) \
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rcu_dereference_check(p, rcu_read_lock_held())
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/**
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* rcu_dereference_bh - fetch an RCU-protected pointer, checking for RCU-bh
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*
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* Makes rcu_dereference_check() do the dirty work.
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*/
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#define rcu_dereference_bh(p) \
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rcu_dereference_check(p, rcu_read_lock_bh_held())
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/**
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* rcu_dereference_sched - fetch RCU-protected pointer, checking for RCU-sched
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*
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* Makes rcu_dereference_check() do the dirty work.
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*/
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#define rcu_dereference_sched(p) \
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rcu_dereference_check(p, rcu_read_lock_sched_held())
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/**
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* rcu_assign_pointer - assign (publicize) a pointer to a newly
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* initialized structure that will be dereferenced by RCU read-side
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* critical sections. Returns the value assigned.
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*
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* Inserts memory barriers on architectures that require them
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* (pretty much all of them other than x86), and also prevents
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* the compiler from reordering the code that initializes the
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* structure after the pointer assignment. More importantly, this
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* call documents which pointers will be dereferenced by RCU read-side
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* code.
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*/
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#define rcu_assign_pointer(p, v) \
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({ \
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if (!__builtin_constant_p(v) || \
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((v) != NULL)) \
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smp_wmb(); \
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(p) = (v); \
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})
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/* Infrastructure to implement the synchronize_() primitives. */
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struct rcu_synchronize {
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struct rcu_head head;
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struct completion completion;
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};
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extern void wakeme_after_rcu(struct rcu_head *head);
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/**
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* call_rcu - Queue an RCU callback for invocation after a grace period.
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* @head: structure to be used for queueing the RCU updates.
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* @func: actual update function to be invoked after the grace period
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*
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* The update function will be invoked some time after a full grace
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* period elapses, in other words after all currently executing RCU
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* read-side critical sections have completed. RCU read-side critical
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* sections are delimited by rcu_read_lock() and rcu_read_unlock(),
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* and may be nested.
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*/
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extern void call_rcu(struct rcu_head *head,
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void (*func)(struct rcu_head *head));
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/**
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* call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
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* @head: structure to be used for queueing the RCU updates.
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* @func: actual update function to be invoked after the grace period
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*
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* The update function will be invoked some time after a full grace
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* period elapses, in other words after all currently executing RCU
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* read-side critical sections have completed. call_rcu_bh() assumes
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* that the read-side critical sections end on completion of a softirq
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* handler. This means that read-side critical sections in process
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* context must not be interrupted by softirqs. This interface is to be
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* used when most of the read-side critical sections are in softirq context.
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* RCU read-side critical sections are delimited by :
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* - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
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* OR
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* - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
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* These may be nested.
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*/
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extern void call_rcu_bh(struct rcu_head *head,
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void (*func)(struct rcu_head *head));
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#endif /* __LINUX_RCUPDATE_H */
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