| Message ID | 1422892200-11817-1-git-send-email-pbonzini@redhat.com |
|---|---|
| State | New |
| Headers | show |
diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c index 41cb23d..50a29d8 100644 --- a/util/qemu-thread-posix.c +++ b/util/qemu-thread-posix.c @@ -307,11 +307,13 @@ static inline void futex_wait(QemuEvent *ev, unsigned val) #else static inline void futex_wake(QemuEvent *ev, int n) { + pthread_mutex_lock(&ev->lock); if (n == 1) { pthread_cond_signal(&ev->cond); } else { pthread_cond_broadcast(&ev->cond); } + pthread_mutex_unlock(&ev->lock); } static inline void futex_wait(QemuEvent *ev, unsigned val)
This had a possible deadlock that was visible with rcutorture. qemu_event_set qemu_event_wait ---------------------------------------------------------------- cmpxchg reads FREE, writes BUSY futex_wait: pthread_mutex_lock futex_wait: value == BUSY xchg reads BUSY, writes SET futex_wake: pthread_cond_broadcast futex_wait: pthread_cond_wait <deadlock> The fix is simply to avoid condvar tricks and do the obvious locking around pthread_cond_broadcast: qemu_event_set qemu_event_wait ---------------------------------------------------------------- cmpxchg reads FREE, writes BUSY futex_wait: pthread_mutex_lock futex_wait: value == BUSY xchg reads BUSY, writes SET futex_wake: pthread_mutex_lock (blocks) futex_wait: pthread_cond_wait (mutex unlocked) futex_wake: pthread_cond_broadcast futex_wake: pthread_mutex_unlock futex_wait: pthread_mutex_unlock Cc: qemu-stable@nongnu.org Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> --- util/qemu-thread-posix.c | 2 ++ 1 file changed, 2 insertions(+)