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+rene...@ideasonboard.com> > --- > 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 majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
