diff options
Diffstat (limited to 'util')
| -rw-r--r-- | util/qemu-thread-posix.c | 15 | ||||
| -rw-r--r-- | util/qemu-thread-win32.c | 15 | ||||
| -rw-r--r-- | util/rcu.c | 11 |
3 files changed, 29 insertions, 12 deletions
diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c index 74a3023f3e..ce51b37c1d 100644 --- a/util/qemu-thread-posix.c +++ b/util/qemu-thread-posix.c @@ -360,7 +360,11 @@ void qemu_event_destroy(QemuEvent *ev) void qemu_event_set(QemuEvent *ev) { - if (atomic_mb_read(&ev->value) != EV_SET) { + /* qemu_event_set has release semantics, but because it *loads* + * ev->value we need a full memory barrier here. + */ + smp_mb(); + if (atomic_read(&ev->value) != EV_SET) { if (atomic_xchg(&ev->value, EV_SET) == EV_BUSY) { /* There were waiters, wake them up. */ futex_wake(ev, INT_MAX); @@ -370,7 +374,11 @@ void qemu_event_set(QemuEvent *ev) void qemu_event_reset(QemuEvent *ev) { - if (atomic_mb_read(&ev->value) == EV_SET) { + unsigned value; + + value = atomic_read(&ev->value); + smp_mb_acquire(); + if (value == EV_SET) { /* * If there was a concurrent reset (or even reset+wait), * do nothing. Otherwise change EV_SET->EV_FREE. @@ -383,7 +391,8 @@ void qemu_event_wait(QemuEvent *ev) { unsigned value; - value = atomic_mb_read(&ev->value); + value = atomic_read(&ev->value); + smp_mb_acquire(); if (value != EV_SET) { if (value == EV_FREE) { /* diff --git a/util/qemu-thread-win32.c b/util/qemu-thread-win32.c index 98a5ddff82..072806f792 100644 --- a/util/qemu-thread-win32.c +++ b/util/qemu-thread-win32.c @@ -274,7 +274,11 @@ void qemu_event_destroy(QemuEvent *ev) void qemu_event_set(QemuEvent *ev) { - if (atomic_mb_read(&ev->value) != EV_SET) { + /* qemu_event_set has release semantics, but because it *loads* + * ev->value we need a full memory barrier here. + */ + smp_mb(); + if (atomic_read(&ev->value) != EV_SET) { if (atomic_xchg(&ev->value, EV_SET) == EV_BUSY) { /* There were waiters, wake them up. */ SetEvent(ev->event); @@ -284,7 +288,11 @@ void qemu_event_set(QemuEvent *ev) void qemu_event_reset(QemuEvent *ev) { - if (atomic_mb_read(&ev->value) == EV_SET) { + unsigned value; + + value = atomic_read(&ev->value); + smp_mb_acquire(); + if (value == EV_SET) { /* If there was a concurrent reset (or even reset+wait), * do nothing. Otherwise change EV_SET->EV_FREE. */ @@ -296,7 +304,8 @@ void qemu_event_wait(QemuEvent *ev) { unsigned value; - value = atomic_mb_read(&ev->value); + value = atomic_read(&ev->value); + smp_mb_acquire(); if (value != EV_SET) { if (value == EV_FREE) { /* qemu_event_set is not yet going to call SetEvent, but we are diff --git a/util/rcu.c b/util/rcu.c index bceb3e4720..9adc5e4a36 100644 --- a/util/rcu.c +++ b/util/rcu.c @@ -82,14 +82,16 @@ static void wait_for_readers(void) /* Instead of using atomic_mb_set for index->waiting, and * atomic_mb_read for index->ctr, memory barriers are placed * manually since writes to different threads are independent. - * atomic_mb_set has a smp_wmb before... + * qemu_event_reset has acquire semantics, so no memory barrier + * is needed here. */ - smp_wmb(); QLIST_FOREACH(index, ®istry, node) { atomic_set(&index->waiting, true); } - /* ... and a smp_mb after. */ + /* Here, order the stores to index->waiting before the + * loads of index->ctr. + */ smp_mb(); QLIST_FOREACH_SAFE(index, ®istry, node, tmp) { @@ -104,9 +106,6 @@ static void wait_for_readers(void) } } - /* atomic_mb_read has smp_rmb after. */ - smp_rmb(); - if (QLIST_EMPTY(®istry)) { break; } |