librbd: QoS delayed dispatch needs to use op work queue

The QoS throttle will invoke its throttle complete callback within
the scope of the ImageCtx timer lock singleton. This would cause
the potential for deadlock if a future dispatch layer attempted
to acquire the same timer lock.

Signed-off-by: Jason Dillaman <dillaman@redhat.com>

diff --git a/src/librbd/io/QosImageDispatch.cc b/src/librbd/io/QosImageDispatch.cc
index dff10290080c5b43b108e1cd2aa11dc34e56ab75..7776355209b6a9842c8e5162b19686ea927df508 100644 (file)
--- a/src/librbd/io/QosImageDispatch.cc
+++ b/src/librbd/io/QosImageDispatch.cc
@@ -281,7 +281,8 @@ void QosImageDispatch<I>::handle_throttle_ready(Tag&& tag, uint64_t flag) {
                  << "flag=" << flag << dendl;
 
   if (set_throttle_flag(tag.image_dispatch_flags, flag)) {
-    tag.on_dispatched->complete(0);
+    // timer_lock is held -- so dispatch from outside the timer thread
+    m_image_ctx->op_work_queue->queue(tag.on_dispatched, 0);
   }
 }