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rcuwait: Introduce prepare_to and finish_rcuwait

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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>
This commit is contained in:
Davidlohr Bueso 2020-04-23 22:48:35 -07:00 committed by Paolo Bonzini
parent 9d9a6ebfea
commit 5c21f7b322
1 changed files with 16 additions and 5 deletions
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21
include/linux/rcuwait.h
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@ -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; \
})