[media] vb2: fix vb2_thread_stop race conditions

The locking scheme inside the vb2 thread is unsafe when stopping the
thread. In particular kthread_stop was called *after* internal data
structures were cleaned up instead of doing that before. In addition,
internal vb2 functions were called after threadio->stop was set to
true and vb2_internal_streamoff was called. This is also not allowed.

All this led to a variety of race conditions and kernel warnings and/or
oopses.

Fixed by moving the kthread_stop call up before the cleanup takes
place, and by checking threadio->stop before calling internal vb2
queuing operations.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Cc: <stable@vger.kernel.org>      # for v3.16 and up
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
index d09a891..bc08a82 100644 (file)
--- a/drivers/media/v4l2-core/videobuf2-core.c
+++ b/drivers/media/v4l2-core/videobuf2-core.c
@@ -3146,27 +3146,26 @@ static int vb2_thread(void *data)
                        prequeue--;
                } else {
                        call_void_qop(q, wait_finish, q);
-                       ret = vb2_internal_dqbuf(q, &fileio->b, 0);
+                       if (!threadio->stop)
+                               ret = vb2_internal_dqbuf(q, &fileio->b, 0);
                        call_void_qop(q, wait_prepare, q);
                        dprintk(5, "file io: vb2_dqbuf result: %d\n", ret);
                }
-               if (threadio->stop)
-                       break;
-               if (ret)
+               if (ret || threadio->stop)
                        break;
                try_to_freeze();
 
                vb = q->bufs[fileio->b.index];
                if (!(fileio->b.flags & V4L2_BUF_FLAG_ERROR))
-                       ret = threadio->fnc(vb, threadio->priv);
-               if (ret)
-                       break;
+                       if (threadio->fnc(vb, threadio->priv))
+                               break;
                call_void_qop(q, wait_finish, q);
                if (set_timestamp)
                        v4l2_get_timestamp(&fileio->b.timestamp);
-               ret = vb2_internal_qbuf(q, &fileio->b);
+               if (!threadio->stop)
+                       ret = vb2_internal_qbuf(q, &fileio->b);
                call_void_qop(q, wait_prepare, q);
-               if (ret)
+               if (ret || threadio->stop)
                        break;
        }
 
@@ -3235,11 +3234,11 @@ int vb2_thread_stop(struct vb2_queue *q)
        threadio->stop = true;
        vb2_internal_streamoff(q, q->type);
        call_void_qop(q, wait_prepare, q);
+       err = kthread_stop(threadio->thread);
        q->fileio = NULL;
        fileio->req.count = 0;
        vb2_reqbufs(q, &fileio->req);
        kfree(fileio);
-       err = kthread_stop(threadio->thread);
        threadio->thread = NULL;
        kfree(threadio);
        q->fileio = NULL;