Re: [PATCH v4] videobuf2: Add missing lock held on vb2_fop_relase

[Hans Verkuil <hverkuil@xs4all.nl>]

On 11/04/2013 02:54 PM, Ricardo Ribalda Delgado wrote:
> Hello Hans
> 
> Thanks for your comments.
> 
> Please take a look to v4 of this patch
> https://patchwork.linuxtv.org/patch/20529/
> 
> On Mon, Nov 4, 2013 at 1:37 PM, Hans Verkuil <hverkuil@xs4all.nl> wrote:
>> On 11/02/2013 10:53 AM, Ricardo Ribalda Delgado wrote:
>>> From: Ricardo Ribalda <ricardo.ribalda@gmail.com>
>>>
>>> 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:
>>
>> It's also called directly by drivers/media/usb/em28xx/em28xx-video.c!
>>
> 
> em28xx-video does not hold the lock, therefore it can call the normal
> function. On v2 we made a internal function that should be called if
> the funciton is called directly by the driver. Please take a look to
> the old comments. https://patchwork.linuxtv.org/patch/20460/

static int em28xx_v4l2_close(struct file *filp)
{
        struct em28xx_fh *fh  = filp->private_data;
        struct em28xx    *dev = fh->dev;
        int              errCode;

        em28xx_videodbg("users=%d\n", dev->users);

        mutex_lock(&dev->lock);
        vb2_fop_release(filp);
	...

vb2_fop_release(filp) will, with your patch, also try to get dev->lock.

Sylwester's comment re em28xx is incorrect.

> 
>>>
>>> [ 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 ]---
>>>
>>> Signed-off-by: Ricardo Ribalda <ricardo.ribalda@gmail.com>
>>> ---
>>> v2: Comments 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.
>>>
>>> v3: Comments by Sylvester Nawrocki and Mauro Carvalho Chehab
>>>
>>> Use vb2_fop_release_locked instead of __vb2_fop_release
>>>
>>> v4: Comments by Sylvester Nawrocki
>>>
>>> Rename vb2_fop_release_locked to __vb2_fop_release and fix patch format
>>>
>>>  drivers/media/platform/exynos4-is/fimc-capture.c |  2 +-
>>>  drivers/media/platform/exynos4-is/fimc-lite.c    |  2 +-
>>>  drivers/media/v4l2-core/videobuf2-core.c         | 23 ++++++++++++++++++++++-
>>>  include/media/videobuf2-core.h                   |  1 +
>>>  4 files changed, 25 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/media/platform/exynos4-is/fimc-capture.c b/drivers/media/platform/exynos4-is/fimc-capture.c
>>> index fb27ff7..8192fe0 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);
>>>
>>>       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..cbe51cd 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);
>>>       pm_runtime_put(&fimc->pdev->dev);
>>>       clear_bit(ST_FLITE_SUSPENDED, &fimc->state);
>>>
>>> diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
>>> index 594c75e..f48d72a 100644
>>> --- a/drivers/media/v4l2-core/videobuf2-core.c
>>> +++ b/drivers/media/v4l2-core/videobuf2-core.c
>>> @@ -2619,18 +2619,39 @@ 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)
>>> +static 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);
>>>  }
>>> +
>>> +int vb2_fop_release(struct file *file)
>>> +{
>>> +     return _vb2_fop_release(file, false);
>>> +}
>>>  EXPORT_SYMBOL_GPL(vb2_fop_release);
>>>
>>> +int __vb2_fop_release(struct file *file)
>>> +{
>>> +     return _vb2_fop_release(file, true);
>>> +}
>>> +EXPORT_SYMBOL_GPL(__vb2_fop_release);
>>
>> Sorry for introducing yet another opinion, but I think this is very confusing.
> 
> It is confusing the lock_held parameter or the __ naming for unlocked versions?

The naming for the most part. Having a normal function, a '_' prefix and a '__'
prefix is a bit over the top IMHO. I prefer to have a clearly named _unlock
version.

Regards,

	Hans

> 
>>
>> I would do this:
>>
>> static int __vb2_fop_release(struct file *file, struct mutex *lock)
>> {
>>         struct video_device *vdev = video_devdata(file);
>>
>>         if (file->private_data == vdev->queue->owner) {
>>                 if (lock)
>>                         mutex_lock(lock);
>>                 vb2_queue_release(vdev->queue);
>>                 vdev->queue->owner = NULL;
>>                 if (lock)
>>                         mutex_unlock(lock);
>>         }
>>         return v4l2_fh_release(file);
>> }
>>
>> int vb2_fop_release(struct file *file)
>> {
>>         struct video_device *vdev = video_devdata(file);
>>         struct mutex *lock = vdev->queue->lock ?
>>                                 vdev->queue->lock : vdev->lock;
>>
>>         return __vb2_fop_release(file, lock);
>> }
>> EXPORT_SYMBOL_GPL(vb2_fop_release);
>>
>> int vb2_fop_release_unlock(struct file *file)
>> {
>>         return __vb2_fop_release(file, NULL);
>> }
>> EXPORT_SYMBOL_GPL(vb2_fop_release_unlock);
>>
>> Optionally, __vb2_fop_release can be exported and then vb2_fop_release_unlock
>> isn't necessary.
>>
> 
> i dont have any strong opinion in any direction. All I really care is
> that the oops is fixed :).
> 
> If your concern about the patch is the is_lock_held function, I can
> make a patch with the params on your proposal and the __naming as
> Sylvester suggested, so everyone is happy.
> 
> Sylvester, Hanshat do you think?
> 
> Thanks for your comments!
> 
>> Regards,
>>
>>         Hans
>>
>>> +
>>>  ssize_t vb2_fop_write(struct file *file, char __user *buf,
>>>               size_t count, loff_t *ppos)
>>>  {
>>> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
>>> index 6781258..76400fa 100644
>>> --- a/include/media/videobuf2-core.h
>>> +++ b/include/media/videobuf2-core.h
>>> @@ -491,6 +491,7 @@ 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);
>>> +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,
>>>
>>
> 
> 
>