Ping? On 05/23/2014 09:54 AM, Hans Verkuil wrote: > Hi Laurent, > > This patch caused a circular locking dependency as reported by Sasha Levin: > > https://lkml.org/lkml/2014/5/5/366 > > The reason is that copy_to/from_user is called in video_usercopy() with the > core lock held. The copy functions can fault which takes the mmap_sem. If it > was just video_usercopy() then it would be fairly easy to solve this, but > the copy_to_/from_user functions are also called from read and write and they > can be used in other unexpected places. > > I'm not sure if vb2_fop_get_unmapped_area() is a problem. I suspect (but I'm > not sure) that when that one is called the mmap_sem isn't taken, in which > case taking the lock is fine. > > But taking the lock in vb2_fop_mmap() does cause lockdep problems. > > Ideally I would like to drop taking that lock in vb2_fop_mmap and resolve the > race condition that it intended to fix in a different way. > > Regards, > > Hans > > On 08/06/2013 10:10 PM, Laurent Pinchart wrote: >> The vb2_fop_mmap() and vb2_fop_get_unmapped_area() functions are plug-in >> implementation of the mmap() and get_unmapped_area() file operations >> that calls vb2_mmap() and vb2_get_unmapped_area() on the queue >> associated with the video device. Neither the >> vb2_fop_mmap/vb2_fop_get_unmapped_area nor the >> v4l2_mmap/vb2_get_unmapped_area functions in the V4L2 core take any >> lock, leading to race conditions between mmap/get_unmapped_area and >> other buffer-related ioctls such as VIDIOC_REQBUFS. >> >> Fix it by taking the queue or device lock around the vb2_mmap() and >> vb2_get_unmapped_area() calls. >> >> Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@xxxxxxxxxxxxxxxx> >> --- >> drivers/media/v4l2-core/videobuf2-core.c | 18 ++++++++++++++++-- >> 1 file changed, 16 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c >> index 9fc4bab..c9b50c7 100644 >> --- a/drivers/media/v4l2-core/videobuf2-core.c >> +++ b/drivers/media/v4l2-core/videobuf2-core.c >> @@ -2578,8 +2578,15 @@ EXPORT_SYMBOL_GPL(vb2_ioctl_expbuf); >> int vb2_fop_mmap(struct file *file, struct vm_area_struct *vma) >> { >> struct video_device *vdev = video_devdata(file); >> + struct mutex *lock = vdev->queue->lock ? vdev->queue->lock : vdev->lock; >> + int err; >> >> - return vb2_mmap(vdev->queue, vma); >> + if (lock && mutex_lock_interruptible(lock)) >> + return -ERESTARTSYS; >> + err = vb2_mmap(vdev->queue, vma); >> + if (lock) >> + mutex_unlock(lock); >> + return err; >> } >> EXPORT_SYMBOL_GPL(vb2_fop_mmap); >> >> @@ -2685,8 +2692,15 @@ unsigned long vb2_fop_get_unmapped_area(struct file *file, unsigned long addr, >> unsigned long len, unsigned long pgoff, unsigned long flags) >> { >> struct video_device *vdev = video_devdata(file); >> + struct mutex *lock = vdev->queue->lock ? vdev->queue->lock : vdev->lock; >> + int ret; >> >> - return vb2_get_unmapped_area(vdev->queue, addr, len, pgoff, flags); >> + if (lock && mutex_lock_interruptible(lock)) >> + return -ERESTARTSYS; >> + ret = vb2_get_unmapped_area(vdev->queue, addr, len, pgoff, flags); >> + if (lock) >> + mutex_unlock(lock); >> + return ret; >> } >> EXPORT_SYMBOL_GPL(vb2_fop_get_unmapped_area); >> #endif >> > -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
