diff mbox

[v2] videobuf2: Add missing lock held on vb2_fop_relase

Message ID 1382198877-27164-1-git-send-email-ricardo.ribalda@gmail.com (mailing list archive)
State Superseded, archived
Headers

Commit Message

Ricardo Ribalda Delgado Oct. 19, 2013, 4:07 p.m. UTC 
vb2_fop_relase does not held the lock although it is modifying the
queue->owner field.

This could lead to race conditions on the vb2_perform_io function
when multiple applications are accessing the video device via
read/write API:

[ 308.297741] BUG: unable to handle kernel NULL pointer dereference at
0000000000000260
[ 308.297759] IP: [<ffffffffa07a9fd2>] vb2_perform_fileio+0x372/0x610
[videobuf2_core]
[ 308.297794] PGD 159719067 PUD 158119067 PMD 0
[ 308.297812] Oops: 0000 #1 SMP
[ 308.297826] Modules linked in: qt5023_video videobuf2_dma_sg
qtec_xform videobuf2_vmalloc videobuf2_memops videobuf2_core
qtec_white qtec_mem gpio_xilinx qtec_cmosis qtec_pcie fglrx(PO)
spi_xilinx spi_bitbang qt5023
[ 308.297888] CPU: 1 PID: 2189 Comm: java Tainted: P O 3.11.0-qtec-standard #1
[ 308.297919] Hardware name: QTechnology QT5022/QT5022, BIOS
PM_2.1.0.309 X64 05/23/2013
[ 308.297952] task: ffff8801564e1690 ti: ffff88014dc02000 task.ti:
ffff88014dc02000
[ 308.297962] RIP: 0010:[<ffffffffa07a9fd2>] [<ffffffffa07a9fd2>]
vb2_perform_fileio+0x372/0x610 [videobuf2_core]
[ 308.297985] RSP: 0018:ffff88014dc03df8 EFLAGS: 00010202
[ 308.297995] RAX: 0000000000000000 RBX: ffff880158a23000 RCX: dead000000100100
[ 308.298003] RDX: 0000000000000000 RSI: dead000000200200 RDI: 0000000000000000
[ 308.298012] RBP: ffff88014dc03e58 R08: 0000000000000000 R09: 0000000000000001
[ 308.298020] R10: ffffea00051e8380 R11: ffff88014dc03fd8 R12: ffff880158a23070
[ 308.298029] R13: ffff8801549040b8 R14: 0000000000198000 R15: 0000000001887e60
[ 308.298040] FS: 00007f65130d5700(0000) GS:ffff88015ed00000(0000)
knlGS:0000000000000000
[ 308.298049] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 308.298057] CR2: 0000000000000260 CR3: 0000000159630000 CR4: 00000000000007e0
[ 308.298064] Stack:
[ 308.298071] ffff880156416c00 0000000000198000 0000000000000000
ffff880100000001
[ 308.298087] ffff88014dc03f50 00000000810a79ca 0002000000000001
ffff880154904718
[ 308.298101] ffff880156416c00 0000000000198000 ffff880154904338
ffff88014dc03f50
[ 308.298116] Call Trace:
[ 308.298143] [<ffffffffa07aa3c4>] vb2_read+0x14/0x20 [videobuf2_core]
[ 308.298198] [<ffffffffa07aa494>] vb2_fop_read+0xc4/0x120 [videobuf2_core]
[ 308.298252] [<ffffffff8154ee9e>] v4l2_read+0x7e/0xc0
[ 308.298296] [<ffffffff8116e639>] vfs_read+0xa9/0x160
[ 308.298312] [<ffffffff8116e882>] SyS_read+0x52/0xb0
[ 308.298328] [<ffffffff81784179>] tracesys+0xd0/0xd5
[ 308.298335] Code: e5 d6 ff ff 83 3d be 24 00 00 04 89 c2 4c 8b 45 b0
44 8b 4d b8 0f 8f 20 02 00 00 85 d2 75 32 83 83 78 03 00 00 01 4b 8b
44 c5 48 <8b> 88 60 02 00 00 85 c9 0f 84 b0 00 00 00 8b 40 58 89 c2 41
89
[ 308.298487] RIP [<ffffffffa07a9fd2>] vb2_perform_fileio+0x372/0x610
[videobuf2_core]
[ 308.298507] RSP <ffff88014dc03df8>
[ 308.298514] CR2: 0000000000000260
[ 308.298526] ---[ end trace e8f01717c96d1e41 ]---

v2: Add bug found by Sylvester Nawrocki

fimc-capture and fimc-lite where calling vb2_fop_release with the lock held.
Therefore a new __vb2_fop_release function has been created to be used by
drivers that overload the release function.

Signed-off-by: Ricardo Ribalda <ricardo.ribalda@gmail.com>
---
 drivers/media/platform/exynos4-is/fimc-capture.c |  2 +-
 drivers/media/platform/exynos4-is/fimc-lite.c    |  2 +-
 drivers/media/usb/em28xx/em28xx-video.c          |  2 +-
 drivers/media/v4l2-core/videobuf2-core.c         | 18 +++++++++++++++++-
 include/media/videobuf2-core.h                   |  2 ++
 5 files changed, 22 insertions(+), 4 deletions(-)

Comments

Sylwester Nawrocki Oct. 19, 2013, 6:27 p.m. UTC | #1 
On 10/19/2013 06:07 PM, Ricardo Ribalda wrote:
[...]
> ---
>   drivers/media/platform/exynos4-is/fimc-capture.c |  2 +-
>   drivers/media/platform/exynos4-is/fimc-lite.c    |  2 +-
>   drivers/media/usb/em28xx/em28xx-video.c          |  2 +-
>   drivers/media/v4l2-core/videobuf2-core.c         | 18 +++++++++++++++++-
>   include/media/videobuf2-core.h                   |  2 ++
>   5 files changed, 22 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/media/platform/exynos4-is/fimc-capture.c b/drivers/media/platform/exynos4-is/fimc-capture.c
> index fb27ff7..c38d247c 100644
> --- a/drivers/media/platform/exynos4-is/fimc-capture.c
> +++ b/drivers/media/platform/exynos4-is/fimc-capture.c
> @@ -549,7 +549,7 @@ static int fimc_capture_release(struct file *file)
>   		vc->streaming = false;
>   	}
>
> -	ret = vb2_fop_release(file);
> +	ret = __vb2_fop_release(file, true);
>
>   	if (close) {
>   		clear_bit(ST_CAPT_BUSY,&fimc->state);
> diff --git a/drivers/media/platform/exynos4-is/fimc-lite.c b/drivers/media/platform/exynos4-is/fimc-lite.c
> index e5798f7..021d804 100644
> --- a/drivers/media/platform/exynos4-is/fimc-lite.c
> +++ b/drivers/media/platform/exynos4-is/fimc-lite.c
> @@ -546,7 +546,7 @@ static int fimc_lite_release(struct file *file)
>   		mutex_unlock(&entity->parent->graph_mutex);
>   	}
>
> -	vb2_fop_release(file);
> +	__vb2_fop_release(file, true);
>   	pm_runtime_put(&fimc->pdev->dev);
>   	clear_bit(ST_FLITE_SUSPENDED,&fimc->state);
>
> diff --git a/drivers/media/usb/em28xx/em28xx-video.c b/drivers/media/usb/em28xx/em28xx-video.c
> index 9d10334..6a5c147 100644
> --- a/drivers/media/usb/em28xx/em28xx-video.c
> +++ b/drivers/media/usb/em28xx/em28xx-video.c
> @@ -1664,7 +1664,7 @@ static int em28xx_v4l2_close(struct file *filp)
>   	em28xx_videodbg("users=%d\n", dev->users);
>
>   	mutex_lock(&dev->lock);
> -	vb2_fop_release(filp);
> +	__vb2_fop_release(filp, false);

I believe no modifications are needed for this driver.

>   	if (dev->users == 1) {
>   		/* the device is already disconnect,
> diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
> index 594c75e..ce309a8 100644
> --- a/drivers/media/v4l2-core/videobuf2-core.c
> +++ b/drivers/media/v4l2-core/videobuf2-core.c
> @@ -2619,16 +2619,32 @@ int vb2_fop_mmap(struct file *file, struct vm_area_struct *vma)
>   }
>   EXPORT_SYMBOL_GPL(vb2_fop_mmap);
>
> -int vb2_fop_release(struct file *file)
> +int __vb2_fop_release(struct file *file, bool lock_is_held)
>   {
>   	struct video_device *vdev = video_devdata(file);
> +	struct mutex *lock;
>
>   	if (file->private_data == vdev->queue->owner) {
> +		if (lock_is_held)
> +			lock = NULL;
> +		else
> +			lock = vdev->queue->lock ?
> +				vdev->queue->lock : vdev->lock;
> +		if (lock)
> +			mutex_lock(lock);
>   		vb2_queue_release(vdev->queue);
>   		vdev->queue->owner = NULL;
> +		if (lock)
> +			mutex_unlock(lock);
>   	}
>   	return v4l2_fh_release(file);
>   }
> +EXPORT_SYMBOL_GPL(__vb2_fop_release);
> +
> +int vb2_fop_release(struct file *file)
> +{
> +	return __vb2_fop_release(file, false);
> +}
>   EXPORT_SYMBOL_GPL(vb2_fop_release);

It might be better to make it something like:

static int _vb2_fop_release(struct file *file, bool locked)
{
   	struct video_device *vdev = video_devdata(file);
	struct mutex *lock;

   	if (file->private_data == vdev->queue->owner) {
		lock = vdev->queue->lock ?
			vdev->queue->lock : vdev->lock;

		if (lock && !locked)
			mutex_lock(lock);

   		vb2_queue_release(vdev->queue);
    		vdev->queue->owner = NULL;
		if (lock && !locked)
			mutex_unlock(lock);
   	}
    	return v4l2_fh_release(file);
}

int vb2_fop_release(struct file *file)
{
	return _vb2_fop_release(file, false);
}
EXPORT_SYMBOL_GPL(vb2_fop_release);

/*
  * This function should be used instead of vb2_fop_release()
  * if the caller already holds the video queue mutex.
  */
int __vb2_fop_release(struct file *file)
{
	return _vb2_fop_release(file, true);
}
EXPORT_SYMBOL_GPL(__vb2_fop_release);

since __vb2_fop_release(file, false); is basically useless, it is same
as vb2_fop_release(file);

>   ssize_t vb2_fop_write(struct file *file, char __user *buf,
> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> index 6781258..cd1e4d5 100644
> --- a/include/media/videobuf2-core.h
> +++ b/include/media/videobuf2-core.h
> @@ -491,6 +491,8 @@ int vb2_ioctl_expbuf(struct file *file, void *priv,
>
>   int vb2_fop_mmap(struct file *file, struct vm_area_struct *vma);
>   int vb2_fop_release(struct file *file);
> +/* must be used if the lock is held. */

Let's put any comments at the function body, not here.

> +int __vb2_fop_release(struct file *file, bool lock_is_held);

int __vb2_fop_release(struct file *file);

>   ssize_t vb2_fop_write(struct file *file, char __user *buf,
>   		size_t count, loff_t *ppos);
>   ssize_t vb2_fop_read(struct file *file, char __user *buf,

Thanks,
Sylwester
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Ricardo Ribalda Delgado Oct. 19, 2013, 8:08 p.m. UTC | #2 
Hello Sylwester


On Sat, Oct 19, 2013 at 8:27 PM, Sylwester Nawrocki
<sylvester.nawrocki@gmail.com> wrote:
> On 10/19/2013 06:07 PM, Ricardo Ribalda wrote:
> [...]
>>
>> ---
>>   drivers/media/platform/exynos4-is/fimc-capture.c |  2 +-
>>   drivers/media/platform/exynos4-is/fimc-lite.c    |  2 +-
>>   drivers/media/usb/em28xx/em28xx-video.c          |  2 +-
>>   drivers/media/v4l2-core/videobuf2-core.c         | 18 +++++++++++++++++-
>>   include/media/videobuf2-core.h                   |  2 ++
>>   5 files changed, 22 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/media/platform/exynos4-is/fimc-capture.c
>> b/drivers/media/platform/exynos4-is/fimc-capture.c
>> index fb27ff7..c38d247c 100644
>> --- a/drivers/media/platform/exynos4-is/fimc-capture.c
>> +++ b/drivers/media/platform/exynos4-is/fimc-capture.c
>> @@ -549,7 +549,7 @@ static int fimc_capture_release(struct file *file)
>>                 vc->streaming = false;
>>         }
>>
>> -       ret = vb2_fop_release(file);
>> +       ret = __vb2_fop_release(file, true);
>>
>>         if (close) {
>>                 clear_bit(ST_CAPT_BUSY,&fimc->state);
>>
>> diff --git a/drivers/media/platform/exynos4-is/fimc-lite.c
>> b/drivers/media/platform/exynos4-is/fimc-lite.c
>> index e5798f7..021d804 100644
>> --- a/drivers/media/platform/exynos4-is/fimc-lite.c
>> +++ b/drivers/media/platform/exynos4-is/fimc-lite.c
>> @@ -546,7 +546,7 @@ static int fimc_lite_release(struct file *file)
>>                 mutex_unlock(&entity->parent->graph_mutex);
>>         }
>>
>> -       vb2_fop_release(file);
>> +       __vb2_fop_release(file, true);
>>         pm_runtime_put(&fimc->pdev->dev);
>>         clear_bit(ST_FLITE_SUSPENDED,&fimc->state);
>>
>>
>> diff --git a/drivers/media/usb/em28xx/em28xx-video.c
>> b/drivers/media/usb/em28xx/em28xx-video.c
>> index 9d10334..6a5c147 100644
>> --- a/drivers/media/usb/em28xx/em28xx-video.c
>> +++ b/drivers/media/usb/em28xx/em28xx-video.c
>> @@ -1664,7 +1664,7 @@ static int em28xx_v4l2_close(struct file *filp)
>>         em28xx_videodbg("users=%d\n", dev->users);
>>
>>         mutex_lock(&dev->lock);
>> -       vb2_fop_release(filp);
>> +       __vb2_fop_release(filp, false);
>
>
> I believe no modifications are needed for this driver.
>
>
>>         if (dev->users == 1) {
>>                 /* the device is already disconnect,
>> diff --git a/drivers/media/v4l2-core/videobuf2-core.c
>> b/drivers/media/v4l2-core/videobuf2-core.c
>> index 594c75e..ce309a8 100644
>> --- a/drivers/media/v4l2-core/videobuf2-core.c
>> +++ b/drivers/media/v4l2-core/videobuf2-core.c
>> @@ -2619,16 +2619,32 @@ int vb2_fop_mmap(struct file *file, struct
>> vm_area_struct *vma)
>>   }
>>   EXPORT_SYMBOL_GPL(vb2_fop_mmap);
>>
>> -int vb2_fop_release(struct file *file)
>> +int __vb2_fop_release(struct file *file, bool lock_is_held)
>>   {
>>         struct video_device *vdev = video_devdata(file);
>> +       struct mutex *lock;
>>
>>         if (file->private_data == vdev->queue->owner) {
>> +               if (lock_is_held)
>> +                       lock = NULL;
>> +               else
>> +                       lock = vdev->queue->lock ?
>> +                               vdev->queue->lock : vdev->lock;
>> +               if (lock)
>> +                       mutex_lock(lock);
>>                 vb2_queue_release(vdev->queue);
>>                 vdev->queue->owner = NULL;
>> +               if (lock)
>> +                       mutex_unlock(lock);
>>         }
>>         return v4l2_fh_release(file);
>>   }
>> +EXPORT_SYMBOL_GPL(__vb2_fop_release);
>> +
>> +int vb2_fop_release(struct file *file)
>> +{
>> +       return __vb2_fop_release(file, false);
>> +}
>>   EXPORT_SYMBOL_GPL(vb2_fop_release);
>
>
> It might be better to make it something like:
>

The rationale behind my patch (and probably not properly commented) is
that the vb2_fop_release must be used ONLY as a file operantion
handler.

If the user makes its own function for relase the __vb2_fop_release
function must be used and the infrastructure must be notified about
the status of he lock (he is on his own).

I believe my approach is simpler because It has only two functions
(instead of 3) and the user understand the difference of the two
functions just by looking at the arguments. In the future we could
even check statically that  vb2_fop_release is not called inside a
driver.

Anyway, this is just a detail :), the most important part is that the
oops is fixed, and that all the drivers that worked keep working.

Lets wait for more comments and then lets post a new patch (with two
functions and better documentation, or three functions).

Thank you very much for you comments!!!

> static int _vb2_fop_release(struct file *file, bool locked)
>
> {
>         struct video_device *vdev = video_devdata(file);
>         struct mutex *lock;
>
>         if (file->private_data == vdev->queue->owner) {
>                 lock = vdev->queue->lock ?
>                         vdev->queue->lock : vdev->lock;
>
>                 if (lock && !locked)
>
>                         mutex_lock(lock);
>
>                 vb2_queue_release(vdev->queue);
>                 vdev->queue->owner = NULL;
>                 if (lock && !locked)
>                         mutex_unlock(lock);
>         }
>         return v4l2_fh_release(file);
> }
>
> int vb2_fop_release(struct file *file)
> {
>         return _vb2_fop_release(file, false);
> }
> EXPORT_SYMBOL_GPL(vb2_fop_release);
>
> /*
>  * This function should be used instead of vb2_fop_release()
>  * if the caller already holds the video queue mutex.
>  */
> int __vb2_fop_release(struct file *file)
> {
>         return _vb2_fop_release(file, true);
> }
> EXPORT_SYMBOL_GPL(__vb2_fop_release);
>
> since __vb2_fop_release(file, false); is basically useless, it is same
> as vb2_fop_release(file);
>
>
>>   ssize_t vb2_fop_write(struct file *file, char __user *buf,
>> diff --git a/include/media/videobuf2-core.h
>> b/include/media/videobuf2-core.h
>> index 6781258..cd1e4d5 100644
>> --- a/include/media/videobuf2-core.h
>> +++ b/include/media/videobuf2-core.h
>> @@ -491,6 +491,8 @@ int vb2_ioctl_expbuf(struct file *file, void *priv,
>>
>>   int vb2_fop_mmap(struct file *file, struct vm_area_struct *vma);
>>   int vb2_fop_release(struct file *file);
>> +/* must be used if the lock is held. */
>
>
> Let's put any comments at the function body, not here.
>
>> +int __vb2_fop_release(struct file *file, bool lock_is_held);
>
>
> int __vb2_fop_release(struct file *file);
>
>
>>   ssize_t vb2_fop_write(struct file *file, char __user *buf,
>>                 size_t count, loff_t *ppos);
>>   ssize_t vb2_fop_read(struct file *file, char __user *buf,
>
>
> Thanks,
> Sylwester
Ricardo Ribalda Delgado Oct. 29, 2013, 10:08 a.m. UTC | #3 
Hello

Anybody has a comment here? If not I will post a patch with the
modifications propossed by Sylwester.


Thanks!

On Sat, Oct 19, 2013 at 10:08 PM, Ricardo Ribalda Delgado
<ricardo.ribalda@gmail.com> wrote:
> Hello Sylwester
>
>
> On Sat, Oct 19, 2013 at 8:27 PM, Sylwester Nawrocki
> <sylvester.nawrocki@gmail.com> wrote:
>> On 10/19/2013 06:07 PM, Ricardo Ribalda wrote:
>> [...]
>>>
>>> ---
>>>   drivers/media/platform/exynos4-is/fimc-capture.c |  2 +-
>>>   drivers/media/platform/exynos4-is/fimc-lite.c    |  2 +-
>>>   drivers/media/usb/em28xx/em28xx-video.c          |  2 +-
>>>   drivers/media/v4l2-core/videobuf2-core.c         | 18 +++++++++++++++++-
>>>   include/media/videobuf2-core.h                   |  2 ++
>>>   5 files changed, 22 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/media/platform/exynos4-is/fimc-capture.c
>>> b/drivers/media/platform/exynos4-is/fimc-capture.c
>>> index fb27ff7..c38d247c 100644
>>> --- a/drivers/media/platform/exynos4-is/fimc-capture.c
>>> +++ b/drivers/media/platform/exynos4-is/fimc-capture.c
>>> @@ -549,7 +549,7 @@ static int fimc_capture_release(struct file *file)
>>>                 vc->streaming = false;
>>>         }
>>>
>>> -       ret = vb2_fop_release(file);
>>> +       ret = __vb2_fop_release(file, true);
>>>
>>>         if (close) {
>>>                 clear_bit(ST_CAPT_BUSY,&fimc->state);
>>>
>>> diff --git a/drivers/media/platform/exynos4-is/fimc-lite.c
>>> b/drivers/media/platform/exynos4-is/fimc-lite.c
>>> index e5798f7..021d804 100644
>>> --- a/drivers/media/platform/exynos4-is/fimc-lite.c
>>> +++ b/drivers/media/platform/exynos4-is/fimc-lite.c
>>> @@ -546,7 +546,7 @@ static int fimc_lite_release(struct file *file)
>>>                 mutex_unlock(&entity->parent->graph_mutex);
>>>         }
>>>
>>> -       vb2_fop_release(file);
>>> +       __vb2_fop_release(file, true);
>>>         pm_runtime_put(&fimc->pdev->dev);
>>>         clear_bit(ST_FLITE_SUSPENDED,&fimc->state);
>>>
>>>
>>> diff --git a/drivers/media/usb/em28xx/em28xx-video.c
>>> b/drivers/media/usb/em28xx/em28xx-video.c
>>> index 9d10334..6a5c147 100644
>>> --- a/drivers/media/usb/em28xx/em28xx-video.c
>>> +++ b/drivers/media/usb/em28xx/em28xx-video.c
>>> @@ -1664,7 +1664,7 @@ static int em28xx_v4l2_close(struct file *filp)
>>>         em28xx_videodbg("users=%d\n", dev->users);
>>>
>>>         mutex_lock(&dev->lock);
>>> -       vb2_fop_release(filp);
>>> +       __vb2_fop_release(filp, false);
>>
>>
>> I believe no modifications are needed for this driver.
>>
>>
>>>         if (dev->users == 1) {
>>>                 /* the device is already disconnect,
>>> diff --git a/drivers/media/v4l2-core/videobuf2-core.c
>>> b/drivers/media/v4l2-core/videobuf2-core.c
>>> index 594c75e..ce309a8 100644
>>> --- a/drivers/media/v4l2-core/videobuf2-core.c
>>> +++ b/drivers/media/v4l2-core/videobuf2-core.c
>>> @@ -2619,16 +2619,32 @@ int vb2_fop_mmap(struct file *file, struct
>>> vm_area_struct *vma)
>>>   }
>>>   EXPORT_SYMBOL_GPL(vb2_fop_mmap);
>>>
>>> -int vb2_fop_release(struct file *file)
>>> +int __vb2_fop_release(struct file *file, bool lock_is_held)
>>>   {
>>>         struct video_device *vdev = video_devdata(file);
>>> +       struct mutex *lock;
>>>
>>>         if (file->private_data == vdev->queue->owner) {
>>> +               if (lock_is_held)
>>> +                       lock = NULL;
>>> +               else
>>> +                       lock = vdev->queue->lock ?
>>> +                               vdev->queue->lock : vdev->lock;
>>> +               if (lock)
>>> +                       mutex_lock(lock);
>>>                 vb2_queue_release(vdev->queue);
>>>                 vdev->queue->owner = NULL;
>>> +               if (lock)
>>> +                       mutex_unlock(lock);
>>>         }
>>>         return v4l2_fh_release(file);
>>>   }
>>> +EXPORT_SYMBOL_GPL(__vb2_fop_release);
>>> +
>>> +int vb2_fop_release(struct file *file)
>>> +{
>>> +       return __vb2_fop_release(file, false);
>>> +}
>>>   EXPORT_SYMBOL_GPL(vb2_fop_release);
>>
>>
>> It might be better to make it something like:
>>
>
> The rationale behind my patch (and probably not properly commented) is
> that the vb2_fop_release must be used ONLY as a file operantion
> handler.
>
> If the user makes its own function for relase the __vb2_fop_release
> function must be used and the infrastructure must be notified about
> the status of he lock (he is on his own).
>
> I believe my approach is simpler because It has only two functions
> (instead of 3) and the user understand the difference of the two
> functions just by looking at the arguments. In the future we could
> even check statically that  vb2_fop_release is not called inside a
> driver.
>
> Anyway, this is just a detail :), the most important part is that the
> oops is fixed, and that all the drivers that worked keep working.
>
> Lets wait for more comments and then lets post a new patch (with two
> functions and better documentation, or three functions).
>
> Thank you very much for you comments!!!
>
>> static int _vb2_fop_release(struct file *file, bool locked)
>>
>> {
>>         struct video_device *vdev = video_devdata(file);
>>         struct mutex *lock;
>>
>>         if (file->private_data == vdev->queue->owner) {
>>                 lock = vdev->queue->lock ?
>>                         vdev->queue->lock : vdev->lock;
>>
>>                 if (lock && !locked)
>>
>>                         mutex_lock(lock);
>>
>>                 vb2_queue_release(vdev->queue);
>>                 vdev->queue->owner = NULL;
>>                 if (lock && !locked)
>>                         mutex_unlock(lock);
>>         }
>>         return v4l2_fh_release(file);
>> }
>>
>> int vb2_fop_release(struct file *file)
>> {
>>         return _vb2_fop_release(file, false);
>> }
>> EXPORT_SYMBOL_GPL(vb2_fop_release);
>>
>> /*
>>  * This function should be used instead of vb2_fop_release()
>>  * if the caller already holds the video queue mutex.
>>  */
>> int __vb2_fop_release(struct file *file)
>> {
>>         return _vb2_fop_release(file, true);
>> }
>> EXPORT_SYMBOL_GPL(__vb2_fop_release);
>>
>> since __vb2_fop_release(file, false); is basically useless, it is same
>> as vb2_fop_release(file);
>>
>>
>>>   ssize_t vb2_fop_write(struct file *file, char __user *buf,
>>> diff --git a/include/media/videobuf2-core.h
>>> b/include/media/videobuf2-core.h
>>> index 6781258..cd1e4d5 100644
>>> --- a/include/media/videobuf2-core.h
>>> +++ b/include/media/videobuf2-core.h
>>> @@ -491,6 +491,8 @@ int vb2_ioctl_expbuf(struct file *file, void *priv,
>>>
>>>   int vb2_fop_mmap(struct file *file, struct vm_area_struct *vma);
>>>   int vb2_fop_release(struct file *file);
>>> +/* must be used if the lock is held. */
>>
>>
>> Let's put any comments at the function body, not here.
>>
>>> +int __vb2_fop_release(struct file *file, bool lock_is_held);
>>
>>
>> int __vb2_fop_release(struct file *file);
>>
>>
>>>   ssize_t vb2_fop_write(struct file *file, char __user *buf,
>>>                 size_t count, loff_t *ppos);
>>>   ssize_t vb2_fop_read(struct file *file, char __user *buf,
>>
>>
>> Thanks,
>> Sylwester
>
>
>
> --
> Ricardo Ribalda
Mauro Carvalho Chehab Oct. 31, 2013, 1:42 p.m. UTC | #4 
Em Sat, 19 Oct 2013 18:07:57 +0200
Ricardo Ribalda <ricardo.ribalda@gmail.com> escreveu:

> vb2_fop_relase does not held the lock although it is modifying the
> queue->owner field.
> 
> This could lead to race conditions on the vb2_perform_io function
> when multiple applications are accessing the video device via
> read/write API:
> 
> [ 308.297741] BUG: unable to handle kernel NULL pointer dereference at
> 0000000000000260
> [ 308.297759] IP: [<ffffffffa07a9fd2>] vb2_perform_fileio+0x372/0x610
> [videobuf2_core]
> [ 308.297794] PGD 159719067 PUD 158119067 PMD 0
> [ 308.297812] Oops: 0000 #1 SMP
> [ 308.297826] Modules linked in: qt5023_video videobuf2_dma_sg
> qtec_xform videobuf2_vmalloc videobuf2_memops videobuf2_core
> qtec_white qtec_mem gpio_xilinx qtec_cmosis qtec_pcie fglrx(PO)
> spi_xilinx spi_bitbang qt5023
> [ 308.297888] CPU: 1 PID: 2189 Comm: java Tainted: P O 3.11.0-qtec-standard #1
> [ 308.297919] Hardware name: QTechnology QT5022/QT5022, BIOS
> PM_2.1.0.309 X64 05/23/2013
> [ 308.297952] task: ffff8801564e1690 ti: ffff88014dc02000 task.ti:
> ffff88014dc02000
> [ 308.297962] RIP: 0010:[<ffffffffa07a9fd2>] [<ffffffffa07a9fd2>]
> vb2_perform_fileio+0x372/0x610 [videobuf2_core]
> [ 308.297985] RSP: 0018:ffff88014dc03df8 EFLAGS: 00010202
> [ 308.297995] RAX: 0000000000000000 RBX: ffff880158a23000 RCX: dead000000100100
> [ 308.298003] RDX: 0000000000000000 RSI: dead000000200200 RDI: 0000000000000000
> [ 308.298012] RBP: ffff88014dc03e58 R08: 0000000000000000 R09: 0000000000000001
> [ 308.298020] R10: ffffea00051e8380 R11: ffff88014dc03fd8 R12: ffff880158a23070
> [ 308.298029] R13: ffff8801549040b8 R14: 0000000000198000 R15: 0000000001887e60
> [ 308.298040] FS: 00007f65130d5700(0000) GS:ffff88015ed00000(0000)
> knlGS:0000000000000000
> [ 308.298049] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 308.298057] CR2: 0000000000000260 CR3: 0000000159630000 CR4: 00000000000007e0
> [ 308.298064] Stack:
> [ 308.298071] ffff880156416c00 0000000000198000 0000000000000000
> ffff880100000001
> [ 308.298087] ffff88014dc03f50 00000000810a79ca 0002000000000001
> ffff880154904718
> [ 308.298101] ffff880156416c00 0000000000198000 ffff880154904338
> ffff88014dc03f50
> [ 308.298116] Call Trace:
> [ 308.298143] [<ffffffffa07aa3c4>] vb2_read+0x14/0x20 [videobuf2_core]
> [ 308.298198] [<ffffffffa07aa494>] vb2_fop_read+0xc4/0x120 [videobuf2_core]
> [ 308.298252] [<ffffffff8154ee9e>] v4l2_read+0x7e/0xc0
> [ 308.298296] [<ffffffff8116e639>] vfs_read+0xa9/0x160
> [ 308.298312] [<ffffffff8116e882>] SyS_read+0x52/0xb0
> [ 308.298328] [<ffffffff81784179>] tracesys+0xd0/0xd5
> [ 308.298335] Code: e5 d6 ff ff 83 3d be 24 00 00 04 89 c2 4c 8b 45 b0
> 44 8b 4d b8 0f 8f 20 02 00 00 85 d2 75 32 83 83 78 03 00 00 01 4b 8b
> 44 c5 48 <8b> 88 60 02 00 00 85 c9 0f 84 b0 00 00 00 8b 40 58 89 c2 41
> 89
> [ 308.298487] RIP [<ffffffffa07a9fd2>] vb2_perform_fileio+0x372/0x610
> [videobuf2_core]
> [ 308.298507] RSP <ffff88014dc03df8>
> [ 308.298514] CR2: 0000000000000260
> [ 308.298526] ---[ end trace e8f01717c96d1e41 ]---
> 
> v2: Add bug found by Sylvester Nawrocki
> 
> fimc-capture and fimc-lite where calling vb2_fop_release with the lock held.
> Therefore a new __vb2_fop_release function has been created to be used by
> drivers that overload the release function.
> 
> Signed-off-by: Ricardo Ribalda <ricardo.ribalda@gmail.com>
> ---
>  drivers/media/platform/exynos4-is/fimc-capture.c |  2 +-
>  drivers/media/platform/exynos4-is/fimc-lite.c    |  2 +-
>  drivers/media/usb/em28xx/em28xx-video.c          |  2 +-
>  drivers/media/v4l2-core/videobuf2-core.c         | 18 +++++++++++++++++-
>  include/media/videobuf2-core.h                   |  2 ++
>  5 files changed, 22 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/media/platform/exynos4-is/fimc-capture.c b/drivers/media/platform/exynos4-is/fimc-capture.c
> index fb27ff7..c38d247c 100644
> --- a/drivers/media/platform/exynos4-is/fimc-capture.c
> +++ b/drivers/media/platform/exynos4-is/fimc-capture.c
> @@ -549,7 +549,7 @@ static int fimc_capture_release(struct file *file)
>  		vc->streaming = false;
>  	}
>  
> -	ret = vb2_fop_release(file);
> +	ret = __vb2_fop_release(file, true);
>  
>  	if (close) {
>  		clear_bit(ST_CAPT_BUSY, &fimc->state);
> diff --git a/drivers/media/platform/exynos4-is/fimc-lite.c b/drivers/media/platform/exynos4-is/fimc-lite.c
> index e5798f7..021d804 100644
> --- a/drivers/media/platform/exynos4-is/fimc-lite.c
> +++ b/drivers/media/platform/exynos4-is/fimc-lite.c
> @@ -546,7 +546,7 @@ static int fimc_lite_release(struct file *file)
>  		mutex_unlock(&entity->parent->graph_mutex);
>  	}
>  
> -	vb2_fop_release(file);
> +	__vb2_fop_release(file, true);
>  	pm_runtime_put(&fimc->pdev->dev);
>  	clear_bit(ST_FLITE_SUSPENDED, &fimc->state);
>  
> diff --git a/drivers/media/usb/em28xx/em28xx-video.c b/drivers/media/usb/em28xx/em28xx-video.c
> index 9d10334..6a5c147 100644
> --- a/drivers/media/usb/em28xx/em28xx-video.c
> +++ b/drivers/media/usb/em28xx/em28xx-video.c
> @@ -1664,7 +1664,7 @@ static int em28xx_v4l2_close(struct file *filp)
>  	em28xx_videodbg("users=%d\n", dev->users);
>  
>  	mutex_lock(&dev->lock);
> -	vb2_fop_release(filp);
> +	__vb2_fop_release(filp, false);
>  
>  	if (dev->users == 1) {
>  		/* the device is already disconnect,
> diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
> index 594c75e..ce309a8 100644
> --- a/drivers/media/v4l2-core/videobuf2-core.c
> +++ b/drivers/media/v4l2-core/videobuf2-core.c
> @@ -2619,16 +2619,32 @@ int vb2_fop_mmap(struct file *file, struct vm_area_struct *vma)
>  }
>  EXPORT_SYMBOL_GPL(vb2_fop_mmap);
>  
> -int vb2_fop_release(struct file *file)
> +int __vb2_fop_release(struct file *file, bool lock_is_held)
>  {
>  	struct video_device *vdev = video_devdata(file);
> +	struct mutex *lock;
>  
>  	if (file->private_data == vdev->queue->owner) {
> +		if (lock_is_held)
> +			lock = NULL;
> +		else
> +			lock = vdev->queue->lock ?
> +				vdev->queue->lock : vdev->lock;
> +		if (lock)
> +			mutex_lock(lock);
>  		vb2_queue_release(vdev->queue);
>  		vdev->queue->owner = NULL;
> +		if (lock)
> +			mutex_unlock(lock);
>  	}
>  	return v4l2_fh_release(file);
>  }
> +EXPORT_SYMBOL_GPL(__vb2_fop_release);
> +
> +int vb2_fop_release(struct file *file)
> +{
> +	return __vb2_fop_release(file, false);
> +}
>  EXPORT_SYMBOL_GPL(vb2_fop_release);

In general, when a symbol has both locked/unlocked versions, we
use the __symbol for unlocked versions (as the usage of the __symbol
requires the caller do do additional protection).

On this patch, (and on  Sylwester's version) you're seeming to be doing 
just the opposite. That sounds inconsistent with other Kernel symbols.

Please either use that version or add a suffix (like _locked / __unlocked)
to allow a clearer understanding about what's the locked version.

Btw, Does it even make sense to have both options, or wouldn't be better
to just make sure that all drivers will do the same? My concern here is
with race conditions that may happen at device removal, if the lock is
released/retaken inside the routine that unbinds the driver.

Regards,
Mauro

>  
>  ssize_t vb2_fop_write(struct file *file, char __user *buf,
> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> index 6781258..cd1e4d5 100644
> --- a/include/media/videobuf2-core.h
> +++ b/include/media/videobuf2-core.h
> @@ -491,6 +491,8 @@ int vb2_ioctl_expbuf(struct file *file, void *priv,
>  
>  int vb2_fop_mmap(struct file *file, struct vm_area_struct *vma);
>  int vb2_fop_release(struct file *file);
> +/* must be used if the lock is held. */
> +int __vb2_fop_release(struct file *file, bool lock_is_held);
>  ssize_t vb2_fop_write(struct file *file, char __user *buf,
>  		size_t count, loff_t *ppos);
>  ssize_t vb2_fop_read(struct file *file, char __user *buf,
Sylwester Nawrocki Oct. 31, 2013, 2:15 p.m. UTC | #5 
On 31/10/13 14:42, Mauro Carvalho Chehab wrote:
> Em Sat, 19 Oct 2013 18:07:57 +0200
> Ricardo Ribalda <ricardo.ribalda@gmail.com> escreveu:
> 
>> vb2_fop_relase does not held the lock although it is modifying the
>> queue->owner field.
>>
>> This could lead to race conditions on the vb2_perform_io function
>> when multiple applications are accessing the video device via
>> read/write API:
[...]
>> Signed-off-by: Ricardo Ribalda <ricardo.ribalda@gmail.com>
>> ---
>>  drivers/media/platform/exynos4-is/fimc-capture.c |  2 +-
>>  drivers/media/platform/exynos4-is/fimc-lite.c    |  2 +-
>>  drivers/media/usb/em28xx/em28xx-video.c          |  2 +-
>>  drivers/media/v4l2-core/videobuf2-core.c         | 18 +++++++++++++++++-
>>  include/media/videobuf2-core.h                   |  2 ++
>>  5 files changed, 22 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/media/platform/exynos4-is/fimc-capture.c b/drivers/media/platform/exynos4-is/fimc-capture.c
>> index fb27ff7..c38d247c 100644
>> --- a/drivers/media/platform/exynos4-is/fimc-capture.c
>> +++ b/drivers/media/platform/exynos4-is/fimc-capture.c
>> @@ -549,7 +549,7 @@ static int fimc_capture_release(struct file *file)
>>  		vc->streaming = false;
>>  	}
>>  
>> -	ret = vb2_fop_release(file);
>> +	ret = __vb2_fop_release(file, true);
>>  
>>  	if (close) {
>>  		clear_bit(ST_CAPT_BUSY, &fimc->state);
>> diff --git a/drivers/media/platform/exynos4-is/fimc-lite.c b/drivers/media/platform/exynos4-is/fimc-lite.c
>> index e5798f7..021d804 100644
>> --- a/drivers/media/platform/exynos4-is/fimc-lite.c
>> +++ b/drivers/media/platform/exynos4-is/fimc-lite.c
>> @@ -546,7 +546,7 @@ static int fimc_lite_release(struct file *file)
>>  		mutex_unlock(&entity->parent->graph_mutex);
>>  	}
>>  
>> -	vb2_fop_release(file);
>> +	__vb2_fop_release(file, true);
>>  	pm_runtime_put(&fimc->pdev->dev);
>>  	clear_bit(ST_FLITE_SUSPENDED, &fimc->state);
>>  
>> diff --git a/drivers/media/usb/em28xx/em28xx-video.c b/drivers/media/usb/em28xx/em28xx-video.c
>> index 9d10334..6a5c147 100644
>> --- a/drivers/media/usb/em28xx/em28xx-video.c
>> +++ b/drivers/media/usb/em28xx/em28xx-video.c
>> @@ -1664,7 +1664,7 @@ static int em28xx_v4l2_close(struct file *filp)
>>  	em28xx_videodbg("users=%d\n", dev->users);
>>  
>>  	mutex_lock(&dev->lock);
>> -	vb2_fop_release(filp);
>> +	__vb2_fop_release(filp, false);
>>  
>>  	if (dev->users == 1) {
>>  		/* the device is already disconnect,
>> diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
>> index 594c75e..ce309a8 100644
>> --- a/drivers/media/v4l2-core/videobuf2-core.c
>> +++ b/drivers/media/v4l2-core/videobuf2-core.c
>> @@ -2619,16 +2619,32 @@ int vb2_fop_mmap(struct file *file, struct vm_area_struct *vma)
>>  }
>>  EXPORT_SYMBOL_GPL(vb2_fop_mmap);
>>  
>> -int vb2_fop_release(struct file *file)
>> +int __vb2_fop_release(struct file *file, bool lock_is_held)
>>  {
>>  	struct video_device *vdev = video_devdata(file);
>> +	struct mutex *lock;
>>  
>>  	if (file->private_data == vdev->queue->owner) {
>> +		if (lock_is_held)
>> +			lock = NULL;
>> +		else
>> +			lock = vdev->queue->lock ?
>> +				vdev->queue->lock : vdev->lock;
>> +		if (lock)
>> +			mutex_lock(lock);
>>  		vb2_queue_release(vdev->queue);
>>  		vdev->queue->owner = NULL;
>> +		if (lock)
>> +			mutex_unlock(lock);
>>  	}
>>  	return v4l2_fh_release(file);
>>  }
>> +EXPORT_SYMBOL_GPL(__vb2_fop_release);
>> +
>> +int vb2_fop_release(struct file *file)
>> +{
>> +	return __vb2_fop_release(file, false);
>> +}
>>  EXPORT_SYMBOL_GPL(vb2_fop_release);
> 
> In general, when a symbol has both locked/unlocked versions, we
> use the __symbol for unlocked versions (as the usage of the __symbol
> requires the caller do do additional protection).
> 
> On this patch, (and on  Sylwester's version) you're seeming to be doing 
> just the opposite. That sounds inconsistent with other Kernel symbols.

Actually the version with double underscore prefix in my proposed changes
doesn't take the lock internally (please see below). Hence it follows
the common convention you're ponting out.

> Please either use that version or add a suffix (like _locked / __unlocked)
> to allow a clearer understanding about what's the locked version.
> 
> Btw, Does it even make sense to have both options, or wouldn't be better
> to just make sure that all drivers will do the same? My concern here is
> with race conditions that may happen at device removal, if the lock is
> released/retaken inside the routine that unbinds the driver.

Exactly for this reason, i.e. not needing to release and reacquire lock
in driver release() callback I suggested to have the
int __vb2_fop_release(struct file *file); version, for cases when drivers
use their custom handler and call __vb2_fop_release() from within it with
the lock already held.

static int _vb2_fop_release(struct file *file, bool locked)
{
   	struct video_device *vdev = video_devdata(file);
	struct mutex *lock;

   	if (file->private_data == vdev->queue->owner) {
		lock = vdev->queue->lock ?
			vdev->queue->lock : vdev->lock;

		if (lock && !locked)
			mutex_lock(lock);

   		vb2_queue_release(vdev->queue);
    		vdev->queue->owner = NULL;
		if (lock && !locked)
			mutex_unlock(lock);
   	}
    	return v4l2_fh_release(file);
}

This function takes the lock internally.

int vb2_fop_release(struct file *file)
{
	return _vb2_fop_release(file, false);
}
EXPORT_SYMBOL_GPL(vb2_fop_release);

And this one deesn't.

int __vb2_fop_release(struct file *file)
{
	return _vb2_fop_release(file, true);
}
EXPORT_SYMBOL_GPL(__vb2_fop_release);

It probably makes sense to move the locking out of _vb2_fop_release()
and do it only vb2_fop_release(), even though v4l2_fh_release() may
be unnecessarily called while keeping the mutex.

--
Thanks,
Sylwester
--
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diff mbox

Patch

diff --git a/drivers/media/platform/exynos4-is/fimc-capture.c b/drivers/media/platform/exynos4-is/fimc-capture.c
index fb27ff7..c38d247c 100644
--- a/drivers/media/platform/exynos4-is/fimc-capture.c
+++ b/drivers/media/platform/exynos4-is/fimc-capture.c
@@ -549,7 +549,7 @@  static int fimc_capture_release(struct file *file)
 		vc->streaming = false;
 	}
 
-	ret = vb2_fop_release(file);
+	ret = __vb2_fop_release(file, true);
 
 	if (close) {
 		clear_bit(ST_CAPT_BUSY, &fimc->state);
diff --git a/drivers/media/platform/exynos4-is/fimc-lite.c b/drivers/media/platform/exynos4-is/fimc-lite.c
index e5798f7..021d804 100644
--- a/drivers/media/platform/exynos4-is/fimc-lite.c
+++ b/drivers/media/platform/exynos4-is/fimc-lite.c
@@ -546,7 +546,7 @@  static int fimc_lite_release(struct file *file)
 		mutex_unlock(&entity->parent->graph_mutex);
 	}
 
-	vb2_fop_release(file);
+	__vb2_fop_release(file, true);
 	pm_runtime_put(&fimc->pdev->dev);
 	clear_bit(ST_FLITE_SUSPENDED, &fimc->state);
 
diff --git a/drivers/media/usb/em28xx/em28xx-video.c b/drivers/media/usb/em28xx/em28xx-video.c
index 9d10334..6a5c147 100644
--- a/drivers/media/usb/em28xx/em28xx-video.c
+++ b/drivers/media/usb/em28xx/em28xx-video.c
@@ -1664,7 +1664,7 @@  static int em28xx_v4l2_close(struct file *filp)
 	em28xx_videodbg("users=%d\n", dev->users);
 
 	mutex_lock(&dev->lock);
-	vb2_fop_release(filp);
+	__vb2_fop_release(filp, false);
 
 	if (dev->users == 1) {
 		/* the device is already disconnect,
diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
index 594c75e..ce309a8 100644
--- a/drivers/media/v4l2-core/videobuf2-core.c
+++ b/drivers/media/v4l2-core/videobuf2-core.c
@@ -2619,16 +2619,32 @@  int vb2_fop_mmap(struct file *file, struct vm_area_struct *vma)
 }
 EXPORT_SYMBOL_GPL(vb2_fop_mmap);
 
-int vb2_fop_release(struct file *file)
+int __vb2_fop_release(struct file *file, bool lock_is_held)
 {
 	struct video_device *vdev = video_devdata(file);
+	struct mutex *lock;
 
 	if (file->private_data == vdev->queue->owner) {
+		if (lock_is_held)
+			lock = NULL;
+		else
+			lock = vdev->queue->lock ?
+				vdev->queue->lock : vdev->lock;
+		if (lock)
+			mutex_lock(lock);
 		vb2_queue_release(vdev->queue);
 		vdev->queue->owner = NULL;
+		if (lock)
+			mutex_unlock(lock);
 	}
 	return v4l2_fh_release(file);
 }
+EXPORT_SYMBOL_GPL(__vb2_fop_release);
+
+int vb2_fop_release(struct file *file)
+{
+	return __vb2_fop_release(file, false);
+}
 EXPORT_SYMBOL_GPL(vb2_fop_release);
 
 ssize_t vb2_fop_write(struct file *file, char __user *buf,
diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
index 6781258..cd1e4d5 100644
--- a/include/media/videobuf2-core.h
+++ b/include/media/videobuf2-core.h
@@ -491,6 +491,8 @@  int vb2_ioctl_expbuf(struct file *file, void *priv,
 
 int vb2_fop_mmap(struct file *file, struct vm_area_struct *vma);
 int vb2_fop_release(struct file *file);
+/* must be used if the lock is held. */
+int __vb2_fop_release(struct file *file, bool lock_is_held);
 ssize_t vb2_fop_write(struct file *file, char __user *buf,
 		size_t count, loff_t *ppos);
 ssize_t vb2_fop_read(struct file *file, char __user *buf,