https://github.com/torvalds/linux
Revision 67ec1072b053c15564e6090ab30127895dc77a89 authored by Takashi Iwai on 17 February 2016, 13:30:26 UTC, committed by Takashi Iwai on 18 February 2016, 10:27:52 UTC
A non-atomic PCM stream may take snd_pcm_link_rwsem rw semaphore twice in the same code path, e.g. one in snd_pcm_action_nonatomic() and another in snd_pcm_stream_lock(). Usually this is OK, but when a write lock is issued between these two read locks, the problem happens: the write lock is blocked due to the first reade lock, and the second read lock is also blocked by the write lock. This eventually deadlocks. The reason is the way rwsem manages waiters; it's queued like FIFO, so even if the writer itself doesn't take the lock yet, it blocks all the waiters (including reads) queued after it. As a workaround, in this patch, we replace the standard down_write() with an spinning loop. This is far from optimal, but it's good enough, as the spinning time is supposed to be relatively short for normal PCM operations, and the code paths requiring the write lock aren't called so often. Reported-by: Vinod Koul <vinod.koul@intel.com> Tested-by: Ramesh Babu <ramesh.babu@intel.com> Cc: <stable@vger.kernel.org> # v3.18+ Signed-off-by: Takashi Iwai <tiwai@suse.de>
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Tip revision: 67ec1072b053c15564e6090ab30127895dc77a89 authored by Takashi Iwai on 17 February 2016, 13:30:26 UTC
ALSA: pcm: Fix rwsem deadlock for non-atomic PCM stream
ALSA: pcm: Fix rwsem deadlock for non-atomic PCM stream
Tip revision: 67ec107
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