On 8/15/19 2:28 PM, Hans Verkuil wrote: > The stop_streaming callback is called with the queue lock held. > > But some drivers (vivid being one of them) need to stop a kernel thread > in stop_streaming, and if that kernel thread takes the same queue lock, > then stop_streaming may have to unlock the queue lock, stop the thread, > and lock it again. > > However, if you do that, then you must ensure that no other operations > can take place that can change the list of buffers queued to the driver, > specifically: QBUF, STREAMON/OFF, REQBUFS, CREATE_BUFS. > > __vb2_wait_for_done_vb() also checks for this and won't try to wait for > new buffers if in_stop_streaming is true. > > This issue caused this syzbot report: > > https://syzkaller.appspot.com/bug?extid=736c3aae4af7b50d9683
And also this syzbot report: https://syzkaller.appspot.com/bug?extid=06283a66a648cd073885 > > Signed-off-by: Hans Verkuil <hverkuil-ci...@xs4all.nl> > Reported-by: syzbot+736c3aae4af7b50d9...@syzkaller.appspotmail.com Reported-and-tested-by: syzbot+06283a66a648cd073...@syzkaller.appspotmail.com Regards, Hans > --- > diff --git a/drivers/media/common/videobuf2/videobuf2-core.c > b/drivers/media/common/videobuf2/videobuf2-core.c > index 4489744fbbd9..7c70bb9f6cb8 100644 > --- a/drivers/media/common/videobuf2/videobuf2-core.c > +++ b/drivers/media/common/videobuf2/videobuf2-core.c > @@ -677,6 +677,11 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum > vb2_memory memory, > return -EBUSY; > } > > + if (q->in_stop_streaming) { > + dprintk(1, "reqbufs while the stream is being stopped\n"); > + return -EBUSY; > + } > + > if (q->waiting_in_dqbuf && *count) { > dprintk(1, "another dup()ped fd is waiting for a buffer\n"); > return -EBUSY; > @@ -811,6 +816,11 @@ int vb2_core_create_bufs(struct vb2_queue *q, enum > vb2_memory memory, > unsigned plane_sizes[VB2_MAX_PLANES] = { }; > int ret; > > + if (q->in_stop_streaming) { > + dprintk(1, "create_bufs while the stream is being stopped\n"); > + return -EBUSY; > + } > + > if (q->num_buffers == VB2_MAX_FRAME) { > dprintk(1, "maximum number of buffers already allocated\n"); > return -ENOBUFS; > @@ -1514,6 +1524,11 @@ int vb2_core_qbuf(struct vb2_queue *q, unsigned int > index, void *pb, > struct vb2_buffer *vb; > int ret; > > + if (q->in_stop_streaming) { > + dprintk(1, "qbuf while the stream is being stopped\n"); > + return -EBUSY; > + } > + > if (q->error) { > dprintk(1, "fatal error occurred on queue\n"); > return -EIO; > @@ -1675,6 +1690,11 @@ static int __vb2_wait_for_done_vb(struct vb2_queue *q, > int nonblocking) > return -EBUSY; > } > > + if (q->in_stop_streaming) { > + dprintk(1, "the stream is being stopped, will not wait > for buffers\n"); > + return -EINVAL; > + } > + > if (!q->streaming) { > dprintk(1, "streaming off, will not wait for > buffers\n"); > return -EINVAL; > @@ -1716,7 +1736,7 @@ static int __vb2_wait_for_done_vb(struct vb2_queue *q, > int nonblocking) > dprintk(3, "will sleep waiting for buffers\n"); > ret = wait_event_interruptible(q->done_wq, > !list_empty(&q->done_list) || !q->streaming || > - q->error); > + q->in_stop_streaming || q->error); > > /* > * We need to reevaluate both conditions again after reacquiring > @@ -1866,12 +1886,18 @@ static void __vb2_queue_cancel(struct vb2_queue *q) > { > unsigned int i; > > + if (WARN_ON(q->in_stop_streaming)) > + return; > + > /* > * Tell driver to stop all transactions and release all queued > * buffers. > */ > - if (q->start_streaming_called) > + if (q->start_streaming_called) { > + q->in_stop_streaming = 1; > call_void_qop(q, stop_streaming, q); > + q->in_stop_streaming = 0; > + } > > /* > * If you see this warning, then the driver isn't cleaning up properly > @@ -1975,6 +2001,11 @@ int vb2_core_streamon(struct vb2_queue *q, unsigned > int type) > return -EINVAL; > } > > + if (q->in_stop_streaming) { > + dprintk(1, "streamon while the stream is being stopped\n"); > + return -EBUSY; > + } > + > if (q->streaming) { > dprintk(3, "already streaming\n"); > return 0; > @@ -2026,6 +2057,11 @@ int vb2_core_streamoff(struct vb2_queue *q, unsigned > int type) > return -EINVAL; > } > > + if (q->in_stop_streaming) { > + dprintk(1, "streamoff while the stream is being stopped\n"); > + return -EBUSY; > + } > + > /* > * Cancel will pause streaming and remove all buffers from the driver > * and videobuf, effectively returning control over them to userspace. > diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h > index 640aabe69450..c4b7edd25e13 100644 > --- a/include/media/videobuf2-core.h > +++ b/include/media/videobuf2-core.h > @@ -535,6 +535,9 @@ struct vb2_buf_ops { > * @streaming: current streaming state > * @start_streaming_called: @start_streaming was called successfully and we > * started streaming. > + * @in_stop_streaming: set when calling @stop_streaming. While 1, no new > buffers > + * can be queued or created, and neither is it possible to start or > + * stop streaming. > * @error: a fatal error occurred on the queue > * @waiting_for_buffers: used in poll() to check if vb2 is still waiting for > * buffers. Only set for capture queues if qbuf has not yet been > @@ -595,6 +598,7 @@ struct vb2_queue { > > unsigned int streaming:1; > unsigned int start_streaming_called:1; > + unsigned int in_stop_streaming:1; > unsigned int error:1; > unsigned int waiting_for_buffers:1; > unsigned int waiting_in_dqbuf:1; >
