linux-kernel - [PATCH 3.12 27/38] ALSA: pcm : Call kill

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Date:   Tue, 13 Dec 2016 20:52:53 +0100
From:   Jiri Slaby <jslaby@...e.cz>
To:     stable@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Takashi Iwai <tiwai@...e.de>,
        Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 27/38] ALSA: pcm : Call kill_fasync() in stream lock

From: Takashi Iwai <tiwai@...e.de>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 3aa02cb664c5fb1042958c8d1aa8c35055a2ebc4 upstream.

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.

Reported-by: Baozeng Ding <sploving1@...il.com>
Signed-off-by: Takashi Iwai <tiwai@...e.de>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 sound/core/pcm_lib.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
index e1ef106c8a6f..066e91ce9de9 100644
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -1857,10 +1857,10 @@ void snd_pcm_period_elapsed(struct snd_pcm_substream *substream)
 	if (substream->timer_running)
 		snd_timer_interrupt(substream->timer, 1);
  _end:
+	kill_fasync(&runtime->fasync, SIGIO, POLL_IN);
 	snd_pcm_stream_unlock_irqrestore(substream, flags);
 	if (runtime->transfer_ack_end)
 		runtime->transfer_ack_end(substream);
-	kill_fasync(&runtime->fasync, SIGIO, POLL_IN);
 }

 EXPORT_SYMBOL(snd_pcm_period_elapsed);
-- 
2.11.0