blockjob: Wake up BDS when job becomes idle

In the context of draining a BDS, the .drained_poll callback of block
jobs is called. If this returns true (i.e. there is still some activity
pending), the drain operation may call aio_poll() with blocking=true to
wait for completion.

As soon as the pending activity is completed and the job finally arrives
in a quiescent state (i.e. its coroutine either yields with busy=false
or terminates), the block job must notify the aio_poll() loop to wake
up, otherwise we get a deadlock if both are running in different
threads.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>

2 files changed, 16 insertions, 0 deletions

diff --git a/include/block/blockjob.h b/include/block/blockjob.h
index 32c00b7dc0..2290bbb824 100644
--- a/include/block/blockjob.h
+++ b/include/block/blockjob.h
@@ -70,6 +70,9 @@ typedef struct BlockJob {
     /** Called when the job transitions to READY */
     Notifier ready_notifier;
 
+    /** Called when the job coroutine yields or terminates */
+    Notifier idle_notifier;
+
     /** BlockDriverStates that are involved in this block job */
     GSList *nodes;
 } BlockJob;
@@ -119,6 +122,16 @@ int block_job_add_bdrv(BlockJob *job, const char *name, BlockDriverState *bs,
 void block_job_remove_all_bdrv(BlockJob *job);
 
 /**
+ * block_job_wakeup_all_bdrv:
+ * @job: The block job
+ *
+ * Calls bdrv_wakeup() for all BlockDriverStates that have been added to the
+ * job. This function is to be called whenever child_job_drained_poll() would
+ * go from true to false to notify waiting drain requests.
+ */
+void block_job_wakeup_all_bdrv(BlockJob *job);
+
+/**
  * block_job_set_speed:
  * @job: The job to set the speed for.
  * @speed: The new value
diff --git a/include/qemu/job.h b/include/qemu/job.h
index 5cb0681834..b4a784d3cc 100644
--- a/include/qemu/job.h
+++ b/include/qemu/job.h
@@ -156,6 +156,9 @@ typedef struct Job {
     /** Notifiers called when the job transitions to READY */
     NotifierList on_ready;
 
+    /** Notifiers called when the job coroutine yields or terminates */
+    NotifierList on_idle;
+
     /** Element of the list of jobs */
     QLIST_ENTRY(Job) job_list;