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>
100 lines
3.3 KiB
C
100 lines
3.3 KiB
C
/*
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* Read-Copy Update mechanism for mutual exclusion (tree-based version)
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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: Dipankar Sarma <dipankar@in.ibm.com>
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* Paul E. McKenney <paulmck@linux.vnet.ibm.com> Hierarchical algorithm
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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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*
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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_RCUTREE_H
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#define __LINUX_RCUTREE_H
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void rcu_note_context_switch(int cpu);
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#ifndef CONFIG_RCU_NOCB_CPU_ALL
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int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies);
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#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
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void rcu_cpu_stall_reset(void);
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/*
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* Note a virtualization-based context switch. This is simply a
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* wrapper around rcu_note_context_switch(), which allows TINY_RCU
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* to save a few bytes.
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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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rcu_note_context_switch(cpu);
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}
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void synchronize_rcu_bh(void);
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void synchronize_sched_expedited(void);
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void synchronize_rcu_expedited(void);
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void kfree_call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu));
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/**
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* synchronize_rcu_bh_expedited - Brute-force RCU-bh grace period
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*
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* Wait for an RCU-bh grace period to elapse, but use a "big hammer"
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* approach to force the grace period to end quickly. This consumes
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* significant time on all CPUs and is unfriendly to real-time workloads,
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* so is thus not recommended for any sort of common-case code. In fact,
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* if you are using synchronize_rcu_bh_expedited() in a loop, please
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* restructure your code to batch your updates, and then use a single
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* synchronize_rcu_bh() instead.
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*
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* Note that it is illegal to call this function while holding any lock
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* that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
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* to call this function from a CPU-hotplug notifier. Failing to observe
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* these restriction will result in deadlock.
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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_expedited();
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}
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void rcu_barrier(void);
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void rcu_barrier_bh(void);
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void rcu_barrier_sched(void);
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unsigned long get_state_synchronize_rcu(void);
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void cond_synchronize_rcu(unsigned long oldstate);
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extern unsigned long rcutorture_testseq;
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extern unsigned long rcutorture_vernum;
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long rcu_batches_completed(void);
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long rcu_batches_completed_bh(void);
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long rcu_batches_completed_sched(void);
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void rcu_force_quiescent_state(void);
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void rcu_bh_force_quiescent_state(void);
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void rcu_sched_force_quiescent_state(void);
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void exit_rcu(void);
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void rcu_scheduler_starting(void);
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extern int rcu_scheduler_active __read_mostly;
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bool rcu_is_watching(void);
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#endif /* __LINUX_RCUTREE_H */
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