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765a3f4fed
The following pattern is currently not well supported by RCU: 1. Make data element inaccessible to RCU readers. 2. Do work that probably lasts for more than one grace period. 3. Do something to make sure RCU readers in flight before #1 above have completed. Here are some things that could currently be done: a. Do a synchronize_rcu() unconditionally at either #1 or #3 above. This works, but imposes needless work and latency. b. Post an RCU callback at #1 above that does a wakeup, then wait for the wakeup at #3. This works well, but likely results in an extra unneeded grace period. Open-coding this is also a bit more semi-tricky code than would be good. This commit therefore adds get_state_synchronize_rcu() and cond_synchronize_rcu() APIs. Call get_state_synchronize_rcu() at #1 above and pass its return value to cond_synchronize_rcu() at #3 above. This results in a call to synchronize_rcu() if no grace period has elapsed between #1 and #3, but requires only a load, comparison, and memory barrier if a full grace period did elapse. Requested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Peter Zijlstra <peterz@infradead.org>
157 lines
3.3 KiB
C
157 lines
3.3 KiB
C
/*
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* Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
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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, you can access it online at
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* http://www.gnu.org/licenses/gpl-2.0.html.
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*
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* Copyright IBM Corporation, 2008
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*
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* Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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*
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* For detailed explanation of Read-Copy Update mechanism see -
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* Documentation/RCU
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*/
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#ifndef __LINUX_TINY_H
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#define __LINUX_TINY_H
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#include <linux/cache.h>
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static inline unsigned long get_state_synchronize_rcu(void)
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{
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return 0;
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}
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static inline void cond_synchronize_rcu(unsigned long oldstate)
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{
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might_sleep();
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}
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static inline void rcu_barrier_bh(void)
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{
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wait_rcu_gp(call_rcu_bh);
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}
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static inline void rcu_barrier_sched(void)
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{
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wait_rcu_gp(call_rcu_sched);
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}
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static inline void synchronize_rcu_expedited(void)
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{
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synchronize_sched(); /* Only one CPU, so pretty fast anyway!!! */
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}
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static inline void rcu_barrier(void)
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{
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rcu_barrier_sched(); /* Only one CPU, so only one list of callbacks! */
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}
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static inline void synchronize_rcu_bh(void)
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{
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synchronize_sched();
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}
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static inline void synchronize_rcu_bh_expedited(void)
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{
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synchronize_sched();
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}
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static inline void synchronize_sched_expedited(void)
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{
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synchronize_sched();
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}
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static inline void kfree_call_rcu(struct rcu_head *head,
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void (*func)(struct rcu_head *rcu))
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{
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call_rcu(head, func);
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}
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static inline void rcu_note_context_switch(int cpu)
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{
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rcu_sched_qs(cpu);
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}
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/*
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* Take advantage of the fact that there is only one CPU, which
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* allows us to ignore virtualization-based context switches.
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*/
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static inline void rcu_virt_note_context_switch(int cpu)
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{
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}
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/*
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* Return the number of grace periods.
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*/
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static inline long rcu_batches_completed(void)
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{
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return 0;
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}
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/*
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* Return the number of bottom-half grace periods.
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*/
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static inline long rcu_batches_completed_bh(void)
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{
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return 0;
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}
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static inline void rcu_force_quiescent_state(void)
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{
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}
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static inline void rcu_bh_force_quiescent_state(void)
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{
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}
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static inline void rcu_sched_force_quiescent_state(void)
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{
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}
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static inline void rcu_cpu_stall_reset(void)
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{
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}
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static inline void exit_rcu(void)
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{
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}
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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extern int rcu_scheduler_active __read_mostly;
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void rcu_scheduler_starting(void);
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#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
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static inline void rcu_scheduler_starting(void)
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{
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}
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#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
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#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE)
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static inline bool rcu_is_watching(void)
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{
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return __rcu_is_watching();
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}
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#else /* defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */
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static inline bool rcu_is_watching(void)
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{
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return true;
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}
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#endif /* #else defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */
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#endif /* __LINUX_RCUTINY_H */
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