blockjob: Fix hang in block_job_finish_sync

With a mirror job running on a virtio-blk dataplane disk, sending "q" to
HMP will cause a dead loop in block_job_finish_sync.

This is because the aio_poll() only processes the AIO context of bs
which has no more work to do, while the main loop BH that is scheduled
for setting the job->completed flag is never processed.

Fix this by adding a flag in BlockJob structure, to track which context
to poll for the block job to make progress. Its value is set to true
when block_job_coroutine_complete() is called, and is checked in
block_job_finish_sync to determine which context to poll.

Suggested-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
Message-id: 1454379144-29807-1-git-send-email-famz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/block/blockjob.h b/include/block/blockjob.h
index d84ccd8..8bedc49 100644
--- a/include/block/blockjob.h
+++ b/include/block/blockjob.h
@@ -130,6 +130,11 @@ struct BlockJob {
      */
     bool ready;
 
+    /**
+     * Set to true when the job has deferred work to the main loop.
+     */
+    bool deferred_to_main_loop;
+
     /** Status that is published by the query-block-jobs QMP API */
     BlockDeviceIoStatus iostatus;