rcuwait: Introduce prepare_to and finish_rcuwait (5c21f7b3) · Commits · 戴 / test

This allows further flexibility for some callers to implement ad-hoc versions of the generic rcuwait_wait_event(). For example, kvm will need this to maintain tracing semantics. The naming is of course similar to what waitqueue apis offer. Also go ahead and make use of rcu_assign_pointer() for both task writes as it will make the __rcu sparse people happy - this will be the special nil case, thus no added serialization. Acked-by:

Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by:

Davidlohr Bueso <dbueso@suse.de> Message-Id: <20200424054837.5138-4-dave@stgolabs.net> Signed-off-by:

Paolo Bonzini <pbonzini@redhat.com>

include/linux/rcuwait.h

+16 −5

Original line number	Diff line number	Diff line
		@@ -29,12 +29,25 @@ extern int rcuwait_wake_up(struct rcuwait *w);

		/*
		* The caller is responsible for locking around rcuwait_wait_event(),
		* such that writes to @task are properly serialized.
		* and [prepare_to/finish]_rcuwait() such that writes to @task are
		* properly serialized.
		*/

		static inline void prepare_to_rcuwait(struct rcuwait *w)
		{
		rcu_assign_pointer(w->task, current);
		}

		static inline void finish_rcuwait(struct rcuwait *w)
		{
		rcu_assign_pointer(w->task, NULL);
		__set_current_state(TASK_RUNNING);
		}

		#define rcuwait_wait_event(w, condition, state) \
		({ \
		int __ret = 0; \
		rcu_assign_pointer((w)->task, current); \
		prepare_to_rcuwait(w); \
		for (;;) { \
		/* \
		* Implicit barrier (A) pairs with (B) in \
		@@ -51,9 +64,7 @@ extern int rcuwait_wake_up(struct rcuwait *w);
		\
		schedule(); \
		} \
		\
		WRITE_ONCE((w)->task, NULL); \
		__set_current_state(TASK_RUNNING); \
		finish_rcuwait(w); \
		__ret; \
		})

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