[PATCH 4.9 045/139] ALSA: seq: oss: Avoid mutex lock for a long-time ioctl

From: Takashi Iwai tiwai@suse.de

[ Upstream commit 2759caad2600d503c3b0ed800e7e03d2cd7a4c05 ]

Recently we applied a fix to cover the whole OSS sequencer ioctls with the mutex for dealing with the possible races. This works fine in general, but in theory, this may lead to unexpectedly long stall if an ioctl like SNDCTL_SEQ_SYNC is issued and an event with the far future timestamp was queued.

For fixing such a potential stall, this patch changes the mutex lock applied conditionally excluding such an ioctl command. Also, change the mutex_lock() with the interruptible version for user to allow escaping from the big-hammer mutex.

Fixes: 80982c7e834e ("ALSA: seq: oss: Serialize ioctls") Suggested-by: Pavel Machek pavel@ucw.cz Link: https://lore.kernel.org/r/20200922083856.28572-1-tiwai@suse.de Signed-off-by: Takashi Iwai tiwai@suse.de Signed-off-by: Sasha Levin sashal@kernel.org --- sound/core/seq/oss/seq_oss.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/sound/core/seq/oss/seq_oss.c b/sound/core/seq/oss/seq_oss.c index 4b78979599131..ade880fe24a41 100644 --- a/sound/core/seq/oss/seq_oss.c +++ b/sound/core/seq/oss/seq_oss.c @@ -187,9 +187,12 @@ odev_ioctl(struct file *file, unsigned int cmd, unsigned long arg) if (snd_BUG_ON(!dp)) return -ENXIO;

- mutex_lock(&register_mutex); + if (cmd != SNDCTL_SEQ_SYNC && + mutex_lock_interruptible(&register_mutex)) + return -ERESTARTSYS; rc = snd_seq_oss_ioctl(dp, cmd, arg); - mutex_unlock(&register_mutex); + if (cmd != SNDCTL_SEQ_SYNC) + mutex_unlock(&register_mutex); return rc; }