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authorPaolo Bonzini <pbonzini@redhat.com>2015-02-02 16:36:51 +0100
committerPaolo Bonzini <pbonzini@redhat.com>2015-02-02 16:55:09 +0100
commit158ef8cbb7e0fe8bb430310924b8bebe5f186e6e (patch)
treeb8a64778abe8dfcd20d1d43462580d5206b49dd5 /util
parent83761b9244ad2ed39d3cfabe8a0e901ab906f7bf (diff)
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qemu-thread: fix qemu_event without futexes
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>
Diffstat (limited to 'util')
-rw-r--r--util/qemu-thread-posix.c2
1 files changed, 2 insertions, 0 deletions
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)