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89da3b94bb
With this patch rcu_sync has a single state variable and the transition rules become really simple: GP_IDLE - owned by the first rcu_sync_enter() which moves it to GP_ENTER - owned by rcu-callback which moves it to GP_PASSED - owned by the last rcu_sync_exit() which moves it to GP_EXIT - and this is the only "nontrivial" state. rcu-callback moves it back to GP_IDLE unless another enter() comes before a GP pass. If rcu-callback is invoked before the next rcu_sync_exit() it must see gp_count incremented by that enter() and set GP_PASSED. Otherwise, if the next rcu_sync_exit() wins the race, it will move it to GP_REPLAY - owned by rcu-callback which moves it to GP_EXIT Signed-off-by: Oleg Nesterov <oleg@redhat.com> [ paulmck: While here, apply READ_ONCE() and WRITE_ONCE() to ->gp_state. ] [ paulmck: Tweaks to make htmldocs happy. (Reported by kbuild test robot.) ] Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
57 lines
1.5 KiB
C
57 lines
1.5 KiB
C
/* SPDX-License-Identifier: GPL-2.0+ */
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/*
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* RCU-based infrastructure for lightweight reader-writer locking
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*
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* Copyright (c) 2015, Red Hat, Inc.
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*
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* Author: Oleg Nesterov <oleg@redhat.com>
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*/
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#ifndef _LINUX_RCU_SYNC_H_
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#define _LINUX_RCU_SYNC_H_
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#include <linux/wait.h>
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#include <linux/rcupdate.h>
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/* Structure to mediate between updaters and fastpath-using readers. */
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struct rcu_sync {
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int gp_state;
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int gp_count;
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wait_queue_head_t gp_wait;
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struct rcu_head cb_head;
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};
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/**
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* rcu_sync_is_idle() - Are readers permitted to use their fastpaths?
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* @rsp: Pointer to rcu_sync structure to use for synchronization
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*
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* Returns true if readers are permitted to use their fastpaths. Must be
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* invoked within some flavor of RCU read-side critical section.
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*/
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static inline bool rcu_sync_is_idle(struct rcu_sync *rsp)
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{
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RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&
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!rcu_read_lock_bh_held() &&
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!rcu_read_lock_sched_held(),
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"suspicious rcu_sync_is_idle() usage");
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return !READ_ONCE(rsp->gp_state); /* GP_IDLE */
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}
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extern void rcu_sync_init(struct rcu_sync *);
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extern void rcu_sync_enter_start(struct rcu_sync *);
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extern void rcu_sync_enter(struct rcu_sync *);
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extern void rcu_sync_exit(struct rcu_sync *);
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extern void rcu_sync_dtor(struct rcu_sync *);
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#define __RCU_SYNC_INITIALIZER(name) { \
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.gp_state = 0, \
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.gp_count = 0, \
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.gp_wait = __WAIT_QUEUE_HEAD_INITIALIZER(name.gp_wait), \
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}
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#define DEFINE_RCU_SYNC(name) \
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struct rcu_sync name = __RCU_SYNC_INITIALIZER(name)
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#endif /* _LINUX_RCU_SYNC_H_ */
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