[v2,1/2,media] media-device: Fix mutex handling code for ioctl
diff mbox

Message ID fef855a4cd482eb02cff982b01511c893ea6e75d.1459243882.git.mchehab@osg.samsung.com
State New
Headers show

Commit Message

Mauro Carvalho Chehab March 29, 2016, 9:31 a.m. UTC
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@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
---
 drivers/media/media-device.c | 13 ++-----------
 1 file changed, 2 insertions(+), 11 deletions(-)

Comments

Sakari Ailus March 29, 2016, 10:24 a.m. UTC | #1
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@ideasonboard.com>
> Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

Tested-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Shuah Khan March 29, 2016, 1:39 p.m. UTC | #2
On 03/29/2016 04:24 AM, Sakari Ailus wrote:
> 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@ideasonboard.com>
>> Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
> 
> Tested-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> 

Please add my

Ran bind/unbind loop test on both au0828 and snd_usb_audio. On au08282, ran into
the media device lifetime related use-after-free which is a known issue present
in older releases. I did include the following bug fix for my testing: 

media: au0828 fix au0828_v4l2_device_register() to not unlock and free
https://lkml.org/lkml/2016/3/28/453

Tested-by: Shuah Khan <shuahkh@osg.samsung.com>

thanks,
-- Shuah
--
To unsubscribe from this list: send the line "unsubscribe linux-media" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Patch
diff mbox

diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c
index 7bfb2b24f644..6af5e6932271 100644
--- a/drivers/media/media-device.c
+++ b/drivers/media/media-device.c
@@ -90,18 +90,13 @@  static struct media_entity *find_entity(struct media_device *mdev, u32 id)
 
 	id &= ~MEDIA_ENT_ID_FLAG_NEXT;
 
-	mutex_lock(&mdev->graph_mutex);
-
 	media_device_for_each_entity(entity, mdev) {
 		if (((media_entity_id(entity) == id) && !next) ||
 		    ((media_entity_id(entity) > id) && next)) {
-			mutex_unlock(&mdev->graph_mutex);
 			return entity;
 		}
 	}
 
-	mutex_unlock(&mdev->graph_mutex);
-
 	return NULL;
 }
 
@@ -431,6 +426,7 @@  static long media_device_ioctl(struct file *filp, unsigned int cmd,
 	struct media_device *dev = devnode->media_dev;
 	long ret;
 
+	mutex_lock(&dev->graph_mutex);
 	switch (cmd) {
 	case MEDIA_IOC_DEVICE_INFO:
 		ret = media_device_get_info(dev,
@@ -443,29 +439,24 @@  static long media_device_ioctl(struct file *filp, unsigned int cmd,
 		break;
 
 	case MEDIA_IOC_ENUM_LINKS:
-		mutex_lock(&dev->graph_mutex);
 		ret = media_device_enum_links(dev,
 				(struct media_links_enum __user *)arg);
-		mutex_unlock(&dev->graph_mutex);
 		break;
 
 	case MEDIA_IOC_SETUP_LINK:
-		mutex_lock(&dev->graph_mutex);
 		ret = media_device_setup_link(dev,
 				(struct media_link_desc __user *)arg);
-		mutex_unlock(&dev->graph_mutex);
 		break;
 
 	case MEDIA_IOC_G_TOPOLOGY:
-		mutex_lock(&dev->graph_mutex);
 		ret = media_device_get_topology(dev,
 				(struct media_v2_topology __user *)arg);
-		mutex_unlock(&dev->graph_mutex);
 		break;
 
 	default:
 		ret = -ENOIOCTLCMD;
 	}
+	mutex_unlock(&dev->graph_mutex);
 
 	return ret;
 }