On Wed, Nov 28, 2018 at 09:37:42AM +0100, hverkuil-cisco@xxxxxxxxx wrote: > From: Hans Verkuil <hverkuil-cisco@xxxxxxxxx> > > While improving the v4l2-compliance tests I came across several vb2 > problems. > > After modifying v4l2-compliance I was now able to use the vivid error > injection feature to test what happens if VIDIOC_STREAMON fails and > a following STREAMON succeeds. > > This generated patches 1/5 and 4/5+5/5. > > Patch 1/5 fixes an issue that was never noticed before since it didn't > result in kernel oopses or warnings, but after the second STREAMON it > won't call start_streaming anymore until you call REQBUFS(0) or close > the device node. > > Patches 4 and 5 are request specific fixes for the same corner case: > the code would unbind (in vb2) or complete (in vivid) a request if > start_streaming fails, but it should just leave things as-is. The > buffer is just put back in the queue, ready for the next attempt at > STREAMON. > > Patch 2/5 was also discovered by v4l2-compliance: the request fd in > v4l2_buffer should be ignored by VIDIOC_PREPARE_BUF, but it wasn't. > > Patch 3/5 fixes a nasty corner case: a buffer with associated request > is queued, and then the request fd is closed by v4l2-compliance. > > When the driver calls vb2_buffer_done, the buffer request object is > unbound, the object is put, and indirectly the associated request > is put as well, and since that was the last references to the request > the whole request is released, which requires the ability to call > mutex_lock. But vb2_buffer_done is atomic (it can be called > from interrupt context), so this shouldn't happen. > > vb2 now takes an extra refcount to the request on qbuf and releases > it on dqbuf and at two other places where an internal dqbuf is done. > > Note that 'skip request checks for VIDIOC_PREPARE_BUF' is a duplicate > of https://patchwork.linuxtv.org/patch/53171/, which is now marked as > superseded. > > I've marked all these patches for 4.20, but I think it is also possible > to apply them for 4.21 since the request API is only used by virtual > drivers and a staging driver. For patches 2--5: Acked-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx> -- Sakari Ailus e-mail: sakari.ailus@xxxxxx
