[PATCH 4.4 019/105] ALSA: seq: Remove spurious WARN_ON() at timer check

[Greg Kroah-Hartman]

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

------------------

From: Takashi Iwai <tiwai@xxxxxxx>

commit 43a3542870328601be02fcc9d27b09db467336ef upstream.

The use of snd_BUG_ON() in ALSA sequencer timer may lead to a spurious
WARN_ON() when a slave timer is deployed as its backend and a
corresponding master timer stops meanwhile.  The symptom was triggered
by syzkaller spontaneously.

Since the NULL timer is valid there, rip off snd_BUG_ON().

Reported-by: syzbot <syzkaller@xxxxxxxxxxxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 sound/core/seq/seq_timer.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/sound/core/seq/seq_timer.c
+++ b/sound/core/seq/seq_timer.c
@@ -355,7 +355,7 @@ static int initialize_timer(struct snd_s
 	unsigned long freq;
 
 	t = tmr->timeri->timer;
-	if (snd_BUG_ON(!t))
+	if (!t)
 		return -EINVAL;
 
 	freq = tmr->preferred_resolution;