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| author | Paolo Bonzini <pbonzini@redhat.com> | 2015-02-02 16:36:51 +0100 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2015-02-02 16:55:09 +0100 |
| commit | 158ef8cbb7e0fe8bb430310924b8bebe5f186e6e (patch) | |
| tree | b8a64778abe8dfcd20d1d43462580d5206b49dd5 /block.c | |
| parent | 83761b9244ad2ed39d3cfabe8a0e901ab906f7bf (diff) | |
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 'block.c')
0 files changed, 0 insertions, 0 deletions