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locks: retry turnstile/sleepq loops on failed cmpset

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In order to go to sleep threads set waiter flags, but that can spuriously
fail e.g. when a new reader arrives. Instead of unlocking everything and
looping back, re-evaluate the new state while still holding the lock necessary
to go to sleep.
This commit is contained in:
mjg 2017-11-25 20:10:33 +00:00
parent d5c5e62cc7
commit c7ffe8c4e0
2 changed files with 29 additions and 44 deletions
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39
sys/kern/kern_rwlock.c
View File

@ -526,6 +526,7 @@ __rw_rlock_hard(struct rwlock *rw, struct thread *td, uintptr_t v
* recheck its state and restart the loop if needed.
*/
v = RW_READ_VALUE(rw);
retry_ts:
if (__rw_can_read(td, v, false)) {
turnstile_cancel(ts);
continue;
@ -561,12 +562,9 @@ __rw_rlock_hard(struct rwlock *rw, struct thread *td, uintptr_t v
* lock and restart the loop.
*/
if (!(v & RW_LOCK_READ_WAITERS)) {
if (!atomic_cmpset_ptr(&rw->rw_lock, v,
v | RW_LOCK_READ_WAITERS)) {
turnstile_cancel(ts);
v = RW_READ_VALUE(rw);
continue;
}
if (!atomic_fcmpset_ptr(&rw->rw_lock, &v,
v | RW_LOCK_READ_WAITERS))
goto retry_ts;
if (LOCK_LOG_TEST(&rw->lock_object, 0))
CTR2(KTR_LOCK, "%s: %p set read waiters flag",
__func__, rw);
@ -757,7 +755,9 @@ __rw_runlock_hard(struct rwlock *rw, struct thread *td, uintptr_t v
* last reader, so grab the turnstile lock.
*/
turnstile_chain_lock(&rw->lock_object);
v = rw->rw_lock & (RW_LOCK_WAITERS | RW_LOCK_WRITE_SPINNER);
v = RW_READ_VALUE(rw);
retry_ts:
v &= (RW_LOCK_WAITERS | RW_LOCK_WRITE_SPINNER);
MPASS(v & RW_LOCK_WAITERS);
/*
@ -782,12 +782,9 @@ __rw_runlock_hard(struct rwlock *rw, struct thread *td, uintptr_t v
x |= (v & RW_LOCK_READ_WAITERS);
} else
queue = TS_SHARED_QUEUE;
if (!atomic_cmpset_rel_ptr(&rw->rw_lock, RW_READERS_LOCK(1) | v,
x)) {
turnstile_chain_unlock(&rw->lock_object);
v = RW_READ_VALUE(rw);
continue;
}
v |= RW_READERS_LOCK(1);
if (!atomic_fcmpset_rel_ptr(&rw->rw_lock, &v, x))
goto retry_ts;
if (LOCK_LOG_TEST(&rw->lock_object, 0))
CTR2(KTR_LOCK, "%s: %p last succeeded with waiters",
__func__, rw);
@ -983,6 +980,7 @@ __rw_wlock_hard(volatile uintptr_t *c, uintptr_t v LOCK_FILE_LINE_ARG_DEF)
#endif
ts = turnstile_trywait(&rw->lock_object);
v = RW_READ_VALUE(rw);
retry_ts:
owner = lv_rw_wowner(v);
#ifdef ADAPTIVE_RWLOCKS
@ -1010,16 +1008,14 @@ __rw_wlock_hard(volatile uintptr_t *c, uintptr_t v LOCK_FILE_LINE_ARG_DEF)
x = v & (RW_LOCK_WAITERS | RW_LOCK_WRITE_SPINNER);
if ((v & ~x) == RW_UNLOCKED) {
x &= ~RW_LOCK_WRITE_SPINNER;
if (atomic_cmpset_acq_ptr(&rw->rw_lock, v, tid | x)) {
if (atomic_fcmpset_acq_ptr(&rw->rw_lock, &v, tid | x)) {
if (x)
turnstile_claim(ts);
else
turnstile_cancel(ts);
break;
}
turnstile_cancel(ts);
v = RW_READ_VALUE(rw);
continue;
goto retry_ts;
}
/*
* If the RW_LOCK_WRITE_WAITERS flag isn't set, then try to
@ -1027,12 +1023,9 @@ __rw_wlock_hard(volatile uintptr_t *c, uintptr_t v LOCK_FILE_LINE_ARG_DEF)
* again.
*/
if (!(v & RW_LOCK_WRITE_WAITERS)) {
if (!atomic_cmpset_ptr(&rw->rw_lock, v,
v | RW_LOCK_WRITE_WAITERS)) {
turnstile_cancel(ts);
v = RW_READ_VALUE(rw);
continue;
}
if (!atomic_fcmpset_ptr(&rw->rw_lock, &v,
v | RW_LOCK_WRITE_WAITERS))
goto retry_ts;
if (LOCK_LOG_TEST(&rw->lock_object, 0))
CTR2(KTR_LOCK, "%s: %p set write waiters flag",
__func__, rw);

34
sys/kern/kern_sx.c
View File

@ -665,6 +665,7 @@ _sx_xlock_hard(struct sx *sx, uintptr_t x, int opts LOCK_FILE_LINE_ARG_DEF)
sleepq_lock(&sx->lock_object);
x = SX_READ_VALUE(sx);
retry_sleepq:
/*
* If the lock was released while spinning on the
@ -704,17 +705,13 @@ _sx_xlock_hard(struct sx *sx, uintptr_t x, int opts LOCK_FILE_LINE_ARG_DEF)
* fail, restart the loop.
*/
if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) {
if (atomic_cmpset_acq_ptr(&sx->sx_lock,
SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS,
tid | SX_LOCK_EXCLUSIVE_WAITERS)) {
sleepq_release(&sx->lock_object);
CTR2(KTR_LOCK, "%s: %p claimed by new writer",
__func__, sx);
break;
}
if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x,
tid | SX_LOCK_EXCLUSIVE_WAITERS))
goto retry_sleepq;
sleepq_release(&sx->lock_object);
x = SX_READ_VALUE(sx);
continue;
CTR2(KTR_LOCK, "%s: %p claimed by new writer",
__func__, sx);
break;
}
/*
@ -722,11 +719,9 @@ _sx_xlock_hard(struct sx *sx, uintptr_t x, int opts LOCK_FILE_LINE_ARG_DEF)
* than loop back and retry.
*/
if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
if (!atomic_cmpset_ptr(&sx->sx_lock, x,
if (!atomic_fcmpset_ptr(&sx->sx_lock, &x,
x | SX_LOCK_EXCLUSIVE_WAITERS)) {
sleepq_release(&sx->lock_object);
x = SX_READ_VALUE(sx);
continue;
goto retry_sleepq;
}
if (LOCK_LOG_TEST(&sx->lock_object, 0))
CTR2(KTR_LOCK, "%s: %p set excl waiters flag",
@ -986,7 +981,7 @@ _sx_slock_hard(struct sx *sx, int opts, uintptr_t x LOCK_FILE_LINE_ARG_DEF)
*/
sleepq_lock(&sx->lock_object);
x = SX_READ_VALUE(sx);
retry_sleepq:
/*
* The lock could have been released while we spun.
* In this case loop back and retry.
@ -1019,12 +1014,9 @@ _sx_slock_hard(struct sx *sx, int opts, uintptr_t x LOCK_FILE_LINE_ARG_DEF)
* back.
*/
if (!(x & SX_LOCK_SHARED_WAITERS)) {
if (!atomic_cmpset_ptr(&sx->sx_lock, x,
x | SX_LOCK_SHARED_WAITERS)) {
sleepq_release(&sx->lock_object);
x = SX_READ_VALUE(sx);
continue;
}
if (!atomic_fcmpset_ptr(&sx->sx_lock, &x,
x | SX_LOCK_SHARED_WAITERS))
goto retry_sleepq;
if (LOCK_LOG_TEST(&sx->lock_object, 0))
CTR2(KTR_LOCK, "%s: %p set shared waiters flag",
__func__, sx);