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rwlock: unlock before traversing threads to wake up

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While here perform a minor cleanup of the unlock path.
This commit is contained in:
Mateusz Guzik 2017-11-17 02:26:15 +00:00
parent 8448e02081
commit 8fef6b2c67
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=325921
1 changed files with 11 additions and 9 deletions
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20
sys/kern/kern_rwlock.c
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@ -1081,7 +1081,7 @@ __rw_wunlock_hard(volatile uintptr_t *c, uintptr_t tid, const char *file,
{
struct rwlock *rw;
struct turnstile *ts;
uintptr_t v;
uintptr_t v, setv;
int queue;
if (SCHEDULER_STOPPED())
@ -1108,8 +1108,6 @@ __rw_wunlock_hard(volatile uintptr_t *c, uintptr_t tid, const char *file,
CTR2(KTR_LOCK, "%s: %p contested", __func__, rw);
turnstile_chain_lock(&rw->lock_object);
ts = turnstile_lookup(&rw->lock_object);
MPASS(ts != NULL);
/*
* Use the same algo as sx locks for now. Prefer waking up shared
@ -1127,19 +1125,23 @@ __rw_wunlock_hard(volatile uintptr_t *c, uintptr_t tid, const char *file,
* there that could be worked around either by waking both queues
* of waiters or doing some complicated lock handoff gymnastics.
*/
v = RW_UNLOCKED;
if (rw->rw_lock & RW_LOCK_WRITE_WAITERS) {
setv = RW_UNLOCKED;
v = RW_READ_VALUE(rw);
queue = TS_SHARED_QUEUE;
if (v & RW_LOCK_WRITE_WAITERS) {
queue = TS_EXCLUSIVE_QUEUE;
v |= (rw->rw_lock & RW_LOCK_READ_WAITERS);
} else
queue = TS_SHARED_QUEUE;
setv |= (v & RW_LOCK_READ_WAITERS);
}
atomic_store_rel_ptr(&rw->rw_lock, setv);
/* Wake up all waiters for the specific queue. */
if (LOCK_LOG_TEST(&rw->lock_object, 0))
CTR3(KTR_LOCK, "%s: %p waking up %s waiters", __func__, rw,
queue == TS_SHARED_QUEUE ? "read" : "write");
ts = turnstile_lookup(&rw->lock_object);
MPASS(ts != NULL);
turnstile_broadcast(ts, queue);
atomic_store_rel_ptr(&rw->rw_lock, v);
turnstile_unpend(ts, TS_EXCLUSIVE_LOCK);
turnstile_chain_unlock(&rw->lock_object);
}