Author: attilio
Date: Mon Oct 12 15:32:00 2009
New Revision: 197981
URL: http://svn.freebsd.org/changeset/base/197981
Log:
MFC r197643, r197735:
When releasing a read/shared lock we need to use a write memory barrier
in order to avoid, on architectures which doesn't have strong ordered
writes, CPU instructions reordering.
Approved by: re (kib)
Modified:
stable/8/sys/ (props changed)
stable/8/sys/amd64/include/xen/ (props changed)
stable/8/sys/cddl/contrib/opensolaris/ (props changed)
stable/8/sys/contrib/dev/acpica/ (props changed)
stable/8/sys/contrib/pf/ (props changed)
stable/8/sys/dev/xen/xenpci/ (props changed)
stable/8/sys/kern/kern_lock.c
stable/8/sys/kern/kern_rwlock.c
stable/8/sys/kern/kern_sx.c
stable/8/sys/sys/rwlock.h
stable/8/sys/sys/sx.h
Modified: stable/8/sys/kern/kern_lock.c
==============================================================================
--- stable/8/sys/kern/kern_lock.c Mon Oct 12 14:51:19 2009
(r197980)
+++ stable/8/sys/kern/kern_lock.c Mon Oct 12 15:32:00 2009
(r197981)
@@ -238,7 +238,7 @@ wakeupshlk(struct lock *lk, const char *
* and return.
*/
if (LK_SHARERS(x) > 1) {
- if (atomic_cmpset_ptr(&lk->lk_lock, x,
+ if (atomic_cmpset_rel_ptr(&lk->lk_lock, x,
x - LK_ONE_SHARER))
break;
continue;
@@ -251,7 +251,7 @@ wakeupshlk(struct lock *lk, const char *
if ((x & LK_ALL_WAITERS) == 0) {
MPASS((x & ~LK_EXCLUSIVE_SPINNERS) ==
LK_SHARERS_LOCK(1));
- if (atomic_cmpset_ptr(&lk->lk_lock, x, LK_UNLOCKED))
+ if (atomic_cmpset_rel_ptr(&lk->lk_lock, x, LK_UNLOCKED))
break;
continue;
}
@@ -277,7 +277,7 @@ wakeupshlk(struct lock *lk, const char *
queue = SQ_SHARED_QUEUE;
}
- if (!atomic_cmpset_ptr(&lk->lk_lock, LK_SHARERS_LOCK(1) | x,
+ if (!atomic_cmpset_rel_ptr(&lk->lk_lock, LK_SHARERS_LOCK(1) | x,
v)) {
sleepq_release(&lk->lock_object);
continue;
Modified: stable/8/sys/kern/kern_rwlock.c
==============================================================================
--- stable/8/sys/kern/kern_rwlock.c Mon Oct 12 14:51:19 2009
(r197980)
+++ stable/8/sys/kern/kern_rwlock.c Mon Oct 12 15:32:00 2009
(r197981)
@@ -538,7 +538,7 @@ _rw_runlock(struct rwlock *rw, const cha
*/
x = rw->rw_lock;
if (RW_READERS(x) > 1) {
- if (atomic_cmpset_ptr(&rw->rw_lock, x,
+ if (atomic_cmpset_rel_ptr(&rw->rw_lock, x,
x - RW_ONE_READER)) {
if (LOCK_LOG_TEST(&rw->lock_object, 0))
CTR4(KTR_LOCK,
@@ -556,7 +556,8 @@ _rw_runlock(struct rwlock *rw, const cha
if (!(x & RW_LOCK_WAITERS)) {
MPASS((x & ~RW_LOCK_WRITE_SPINNER) ==
RW_READERS_LOCK(1));
- if (atomic_cmpset_ptr(&rw->rw_lock, x, RW_UNLOCKED)) {
+ if (atomic_cmpset_rel_ptr(&rw->rw_lock, x,
+ RW_UNLOCKED)) {
if (LOCK_LOG_TEST(&rw->lock_object, 0))
CTR2(KTR_LOCK, "%s: %p last succeeded",
__func__, rw);
@@ -594,7 +595,7 @@ _rw_runlock(struct rwlock *rw, const cha
x |= (v & RW_LOCK_READ_WAITERS);
} else
queue = TS_SHARED_QUEUE;
- if (!atomic_cmpset_ptr(&rw->rw_lock, RW_READERS_LOCK(1) | v,
+ if (!atomic_cmpset_rel_ptr(&rw->rw_lock, RW_READERS_LOCK(1) | v,
x)) {
turnstile_chain_unlock(&rw->lock_object);
continue;
Modified: stable/8/sys/kern/kern_sx.c
==============================================================================
--- stable/8/sys/kern/kern_sx.c Mon Oct 12 14:51:19 2009 (r197980)
+++ stable/8/sys/kern/kern_sx.c Mon Oct 12 15:32:00 2009 (r197981)
@@ -928,7 +928,7 @@ _sx_sunlock_hard(struct sx *sx, const ch
* so, just drop one and return.
*/
if (SX_SHARERS(x) > 1) {
- if (atomic_cmpset_ptr(&sx->sx_lock, x,
+ if (atomic_cmpset_rel_ptr(&sx->sx_lock, x,
x - SX_ONE_SHARER)) {
if (LOCK_LOG_TEST(&sx->lock_object, 0))
CTR4(KTR_LOCK,
@@ -946,8 +946,8 @@ _sx_sunlock_hard(struct sx *sx, const ch
*/
if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
MPASS(x == SX_SHARERS_LOCK(1));
- if (atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1),
- SX_LOCK_UNLOCKED)) {
+ if (atomic_cmpset_rel_ptr(&sx->sx_lock,
+ SX_SHARERS_LOCK(1), SX_LOCK_UNLOCKED)) {
if (LOCK_LOG_TEST(&sx->lock_object, 0))
CTR2(KTR_LOCK, "%s: %p last succeeded",
__func__, sx);
@@ -970,7 +970,7 @@ _sx_sunlock_hard(struct sx *sx, const ch
* Note that the state of the lock could have changed,
* so if it fails loop back and retry.
*/
- if (!atomic_cmpset_ptr(&sx->sx_lock,
+ if (!atomic_cmpset_rel_ptr(&sx->sx_lock,
SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS,
SX_LOCK_UNLOCKED)) {
sleepq_release(&sx->lock_object);
Modified: stable/8/sys/sys/rwlock.h
==============================================================================
--- stable/8/sys/sys/rwlock.h Mon Oct 12 14:51:19 2009 (r197980)
+++ stable/8/sys/sys/rwlock.h Mon Oct 12 15:32:00 2009 (r197981)
@@ -55,13 +55,6 @@
*
* When the lock is not locked by any thread, it is encoded as a read lock
* with zero waiters.
- *
- * A note about memory barriers. Write locks need to use the same memory
- * barriers as mutexes: _acq when acquiring a write lock and _rel when
- * releasing a write lock. Read locks also need to use an _acq barrier when
- * acquiring a read lock. However, since read locks do not update any
- * locked data (modulo bugs of course), no memory barrier is needed when
- * releasing a read lock.
*/
#define RW_LOCK_READ 0x01
Modified: stable/8/sys/sys/sx.h
==============================================================================
--- stable/8/sys/sys/sx.h Mon Oct 12 14:51:19 2009 (r197980)
+++ stable/8/sys/sys/sx.h Mon Oct 12 15:32:00 2009 (r197981)
@@ -63,13 +63,6 @@
*
* When the lock is not locked by any thread, it is encoded as a
* shared lock with zero waiters.
- *
- * A note about memory barriers. Exclusive locks need to use the same
- * memory barriers as mutexes: _acq when acquiring an exclusive lock
- * and _rel when releasing an exclusive lock. On the other side,
- * shared lock needs to use an _acq barrier when acquiring the lock
- * but, since they don't update any locked data, no memory barrier is
- * needed when releasing a shared lock.
*/
#define SX_LOCK_SHARED 0x01
@@ -200,7 +193,7 @@ __sx_sunlock(struct sx *sx, const char *
uintptr_t x = sx->sx_lock;
if (x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS) ||
- !atomic_cmpset_ptr(&sx->sx_lock, x, x - SX_ONE_SHARER))
+ !atomic_cmpset_rel_ptr(&sx->sx_lock, x, x - SX_ONE_SHARER))
_sx_sunlock_hard(sx, file, line);
}
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