When disconnecting the usbtv device, the sound card is unregistered
from ALSA and the snd member of the usbtv struct is set to NULL. If
the usbtv snd_trigger work is running, this can cause a race condition
where the kernel will attempt to access free'd resources, shown in
[1].
This patch fixes the disconnection code by cancelling any snd_trigger
work before unregistering the sound card from ALSA and checking that
the snd member still exists in the work function.
[1]:
usb 3-1.2: USB disconnect, device number 6
BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
IP: [<ffffffff81093850>] process_one_work+0x30/0x480
PGD 405bbf067 PUD 405bbe067 PMD 0
Call Trace:
[<ffffffff81093ce8>] worker_thread+0x48/0x4e0
[<ffffffff81093ca0>] ? process_one_work+0x480/0x480
[<ffffffff81093ca0>] ? process_one_work+0x480/0x480
[<ffffffff81099998>] kthread+0xd8/0xf0
[<ffffffff815c73c2>] ret_from_fork+0x22/0x40
[<ffffffff810998c0>] ? kthread_worker_fn+0x170/0x170
---[ end trace 0f3dac5c1a38e610 ]---
Signed-off-by: Matthew Leach <matthew@mattleach.net>
Tested-by: Peter Sutton <foxxy@foxdogstudios.com>
Cc: stable@vger.kernel.org
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
2a00932f08