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febd668d37
rcuwait_active only returns whether w->task is not NULL. This is exactly one of the usecases that are mentioned in the documentation for rcu_access_pointer() where it is correct to bypass lockdep checks. This avoids a splat from kvm_vcpu_on_spin(). Reported-by: Wanpeng Li <kernellwp@gmail.com> Tested-by: Wanpeng Li <kernellwp@gmail.com> Acked-by: Davidlohr Bueso <dave@stgolabs.net> Cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
80 lines
1.8 KiB
C
80 lines
1.8 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_RCUWAIT_H_
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#define _LINUX_RCUWAIT_H_
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#include <linux/rcupdate.h>
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#include <linux/sched/signal.h>
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/*
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* rcuwait provides a way of blocking and waking up a single
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* task in an rcu-safe manner.
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*
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* The only time @task is non-nil is when a user is blocked (or
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* checking if it needs to) on a condition, and reset as soon as we
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* know that the condition has succeeded and are awoken.
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*/
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struct rcuwait {
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struct task_struct __rcu *task;
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};
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#define __RCUWAIT_INITIALIZER(name) \
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{ .task = NULL, }
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static inline void rcuwait_init(struct rcuwait *w)
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{
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w->task = NULL;
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}
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/*
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* Note: this provides no serialization and, just as with waitqueues,
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* requires care to estimate as to whether or not the wait is active.
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*/
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static inline int rcuwait_active(struct rcuwait *w)
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{
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return !!rcu_access_pointer(w->task);
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}
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extern int rcuwait_wake_up(struct rcuwait *w);
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/*
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* The caller is responsible for locking around rcuwait_wait_event(),
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* and [prepare_to/finish]_rcuwait() such that writes to @task are
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* properly serialized.
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*/
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static inline void prepare_to_rcuwait(struct rcuwait *w)
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{
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rcu_assign_pointer(w->task, current);
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}
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static inline void finish_rcuwait(struct rcuwait *w)
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{
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rcu_assign_pointer(w->task, NULL);
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__set_current_state(TASK_RUNNING);
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}
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#define rcuwait_wait_event(w, condition, state) \
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({ \
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int __ret = 0; \
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prepare_to_rcuwait(w); \
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for (;;) { \
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/* \
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* Implicit barrier (A) pairs with (B) in \
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* rcuwait_wake_up(). \
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*/ \
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set_current_state(state); \
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if (condition) \
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break; \
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\
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if (signal_pending_state(state, current)) { \
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__ret = -EINTR; \
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break; \
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} \
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\
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schedule(); \
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} \
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finish_rcuwait(w); \
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__ret; \
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})
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#endif /* _LINUX_RCUWAIT_H_ */
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