ALSA: pcm : Call kill_fasync() in stream lock

Currently kill_fasync() is called outside the stream lock in
snd_pcm_period_elapsed().  This is potentially racy, since the stream
may get released even during the irq handler is running.  Although
snd_pcm_release_substream() calls snd_pcm_drop(), this doesn't
guarantee that the irq handler finishes, thus the kill_fasync() call
outside the stream spin lock may be invoked after the substream is
detached, as recently reported by KASAN.

As a quick workaround, move kill_fasync() call inside the stream
lock.  The fasync is rarely used interface, so this shouldn't have a
big impact from the performance POV.

Ideally, we should implement some sync mechanism for the proper finish
of stream and irq handler.  But this oneliner should suffice for most
cases, so far.

Change-Id: Iaebf87120a34e16bd0b259b2cf661aad6b2cc388
Reported-by: Baozeng Ding <sploving1@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 1 insertions, 1 deletions

diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
index 4187bc78900..f438f2ad312 100644
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -1735,10 +1735,10 @@ void snd_pcm_period_elapsed(struct snd_pcm_substream *substream)
 	if (substream->timer_running)
 		snd_timer_interrupt(substream->timer, 1);
  _end:
-	snd_pcm_stream_unlock_irqrestore(substream, flags);
 	if (runtime->transfer_ack_end)
 		runtime->transfer_ack_end(substream);
 	kill_fasync(&runtime->fasync, SIGIO, POLL_IN);
+	snd_pcm_stream_unlock_irqrestore(substream, flags);
 }
 
 EXPORT_SYMBOL(snd_pcm_period_elapsed);