[PATCH 4.4 51/74] ALSA: seq: oss: Dont drain at closing a client

Greg Kroah-Hartman
2016-03-08T00:11:32Z

From: Takashi Iwai <tiwai@suse.de>

commit 197b958c1e76a575d77038cc98b4bebc2134279f upstream.

The OSS sequencer client tries to drain the pending events at
releasing. Unfortunately, as spotted by syzkaller fuzzer, this may
lead to an unkillable process state when the event has been queued at
the far future. Since the process being released can't be signaled
any longer, it remains and waits for the echo-back event in that far
future.

Back to history, the draining feature was implemented at the time we
misinterpreted POSIX definition for blocking file operation.
Actually, such a behavior is superfluous at release, and we should
just release the device as is instead of keeping it up forever.

This patch just removes the draining call that may block the release
for too long time unexpectedly.

BugLink: http://lkml.kernel.org/r/CACT4Y+Y4kD-aBGj37rf-xBw9bH3GMU6P+MYg4W1e-s-paVD2pg@mail.gmail.com
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
sound/core/seq/oss/seq_oss.c | 2 --
sound/core/seq/oss/seq_oss_device.h | 1 -
sound/core/seq/oss/seq_oss_init.c | 16 ----------------
3 files changed, 19 deletions(-)

--- a/sound/core/seq/oss/seq_oss.c
+++ b/sound/core/seq/oss/seq_oss.c
@@ -148,8 +148,6 @@ odev_release(struct inode *inode, struct
if ((dp = file->private_data) == NULL)
return 0;

- snd_seq_oss_drain_write(dp);
-
mutex_lock(&register_mutex);
snd_seq_oss_release(dp);
mutex_unlock(&register_mutex);
--- a/sound/core/seq/oss/seq_oss_device.h
+++ b/sound/core/seq/oss/seq_oss_device.h
@@ -127,7 +127,6 @@ int snd_seq_oss_write(struct seq_oss_dev
unsigned int snd_seq_oss_poll(struct seq_oss_devinfo *dp, struct file *file, poll_table * wait);

void snd_seq_oss_reset(struct seq_oss_devinfo *dp);
-void snd_seq_oss_drain_write(struct seq_oss_devinfo *dp);

/* */
void snd_seq_oss_process_queue(struct seq_oss_devinfo *dp, abstime_t time);
--- a/sound/core/seq/oss/seq_oss_init.c
+++ b/sound/core/seq/oss/seq_oss_init.c
@@ -436,22 +436,6 @@ snd_seq_oss_release(struct seq_oss_devin

/*
- * Wait until the queue is empty (if we don't have nonblock)
- */
-void
-snd_seq_oss_drain_write(struct seq_oss_devinfo *dp)
-{
- if (! dp->timer->running)
- return;
- if (is_write_mode(dp->file_mode) && !is_nonblock_mode(dp->file_mode) &&
- dp->writeq) {
- while (snd_seq_oss_writeq_sync(dp->writeq))
- ;
- }
-}
-
-
-/*
* reset sequencer devices
*/
void