Hi Mauro,
On Tue, Mar 29, 2016 at 06:31:27AM -0300, Mauro Carvalho Chehab wrote:
> Remove two nested mutex left-overs at find_entity and make sure
> that the code won't suffer race conditions if the device is
> being removed while ioctl is being handled nor the topology changes,
> by protecting all ioctls with a mutex at media_device_ioctl().
>
> As reported by Laurent, commit c38077d39c7e ("[media] media-device:
> get rid of the spinlock") introduced a deadlock in the
> MEDIA_IOC_ENUM_LINKS ioctl handler:
>
> [ 2760.127749] INFO: task media-ctl:954 blocked for more than 120 seconds.
> [ 2760.131867] Not tainted 4.5.0+ #357
> [ 2760.134622] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> [ 2760.139310] media-ctl D ffffffc000086bcc 0 954 671 0x00000001
> [ 2760.143618] Call trace:
> [ 2760.145601] [<ffffffc000086bcc>] __switch_to+0x90/0xa4
> [ 2760.148941] [<ffffffc0004e6ef0>] __schedule+0x188/0x5b0
> [ 2760.152309] [<ffffffc0004e7354>] schedule+0x3c/0xa0
> [ 2760.155495] [<ffffffc0004e7768>] schedule_preempt_disabled+0x20/0x38
> [ 2760.159423] [<ffffffc0004e8d28>] __mutex_lock_slowpath+0xc4/0x148
> [ 2760.163217] [<ffffffc0004e8df0>] mutex_lock+0x44/0x5c
> [ 2760.166483] [<ffffffc0003e87d4>] find_entity+0x2c/0xac
> [ 2760.169773] [<ffffffc0003e8d34>] __media_device_enum_links+0x20/0x1dc
> [ 2760.173711] [<ffffffc0003e9718>] media_device_ioctl+0x214/0x33c
> [ 2760.177384] [<ffffffc0003e9eec>] media_ioctl+0x24/0x3c
> [ 2760.180671] [<ffffffc0001bee64>] do_vfs_ioctl+0xac/0x758
> [ 2760.184026] [<ffffffc0001bf594>] SyS_ioctl+0x84/0x98
> [ 2760.187196] [<ffffffc000085d30>] el0_svc_naked+0x24/0x28
>
> That's because find_entity() holds the graph_mutex, but both
> MEDIA_IOC_ENUM_LINKS and MEDIA_IOC_SETUP_LINK logic also take
> the mutex.
>
> Reported-by: Laurent Pinchart <laurent.pinchart+renesas@xxxxxxxxxxxxxxxx>
> Signed-off-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxx>
Tested-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
--
Sakari Ailus
e-mail: sakari.ailus@xxxxxx XMPP: sailus@xxxxxxxxxxxxxx
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