Author: mjg
Date: Fri Nov 17 02:26:15 2017
New Revision: 325921
URL: https://svnweb.freebsd.org/changeset/base/325921
Log:
rwlock: unlock before traversing threads to wake up
While here perform a minor cleanup of the unlock path.
Modified:
head/sys/kern/kern_rwlock.c
Modified: head/sys/kern/kern_rwlock.c
==============================================================================
--- head/sys/kern/kern_rwlock.c Fri Nov 17 02:25:04 2017 (r325920)
+++ head/sys/kern/kern_rwlock.c Fri Nov 17 02:26:15 2017 (r325921)
@@ -1081,7 +1081,7 @@ __rw_wunlock_hard(volatile uintptr_t *c, uintptr_t tid
{
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
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
* 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);
}
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