[Qemu-devel] [PATCH v4 4/5] mirror: follow AioContext change gracefully

[Stefan Hajnoczi]

Add block_job_pause_point() calls to mark quiescent points and make sure
to complete in-flight requests when switching AioContexts.

This patch solves undefined behavior in the mirror block job when the
BDS AioContext is changed by dataplane.

Signed-off-by: Stefan Hajnoczi <address@hidden>
Signed-off-by: Fam Zheng <address@hidden>
---
 block/mirror.c | 45 +++++++++++++++++++++++++++++++++++++--------
 1 file changed, 37 insertions(+), 8 deletions(-)

diff --git a/block/mirror.c b/block/mirror.c
index 80fd3c7..4c4e55b 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -331,6 +331,8 @@ static uint64_t coroutine_fn 
mirror_iteration(MirrorBlockJob *s)
         mirror_wait_for_io(s);
     }
 
+    block_job_pause_point(&s->common);
+
     /* Find the number of consective dirty chunks following the first dirty
      * one, and wait for in flight requests in them. */
     while (nb_chunks * sectors_per_chunk < (s->buf_size >> BDRV_SECTOR_BITS)) {
@@ -581,6 +583,8 @@ static void coroutine_fn mirror_run(void *opaque)
             if (now - last_pause_ns > SLICE_TIME) {
                 last_pause_ns = now;
                 block_job_sleep_ns(&s->common, QEMU_CLOCK_REALTIME, 0);
+            } else {
+                block_job_pause_point(&s->common);
             }
 
             if (block_job_is_cancelled(&s->common)) {
@@ -612,6 +616,8 @@ static void coroutine_fn mirror_run(void *opaque)
             goto immediate_exit;
         }
 
+        block_job_pause_point(&s->common);
+
         cnt = bdrv_get_dirty_count(s->dirty_bitmap);
         /* s->common.offset contains the number of bytes already processed so
          * far, cnt is the number of dirty sectors remaining and
@@ -781,18 +787,41 @@ static void mirror_complete(BlockJob *job, Error **errp)
     block_job_enter(&s->common);
 }
 
+/* There is no matching mirror_resume() because mirror_run() will begin
+ * iterating again when the job is resumed.
+ */
+static void mirror_pause(BlockJob *job)
+{
+    MirrorBlockJob *s = container_of(job, MirrorBlockJob, common);
+
+    while (s->in_flight > 0) {
+        aio_poll(blk_get_aio_context(job->blk), true);
+    }
+}
+
+static void mirror_attached_aio_context(BlockJob *job, AioContext *new_context)
+{
+    MirrorBlockJob *s = container_of(job, MirrorBlockJob, common);
+
+    blk_set_aio_context(s->target, new_context);
+}
+
 static const BlockJobDriver mirror_job_driver = {
-    .instance_size = sizeof(MirrorBlockJob),
-    .job_type      = BLOCK_JOB_TYPE_MIRROR,
-    .set_speed     = mirror_set_speed,
-    .complete      = mirror_complete,
+    .instance_size          = sizeof(MirrorBlockJob),
+    .job_type               = BLOCK_JOB_TYPE_MIRROR,
+    .set_speed              = mirror_set_speed,
+    .complete               = mirror_complete,
+    .pause                  = mirror_pause,
+    .attached_aio_context   = mirror_attached_aio_context,
 };
 
 static const BlockJobDriver commit_active_job_driver = {
-    .instance_size = sizeof(MirrorBlockJob),
-    .job_type      = BLOCK_JOB_TYPE_COMMIT,
-    .set_speed     = mirror_set_speed,
-    .complete      = mirror_complete,
+    .instance_size          = sizeof(MirrorBlockJob),
+    .job_type               = BLOCK_JOB_TYPE_COMMIT,
+    .set_speed              = mirror_set_speed,
+    .complete               = mirror_complete,
+    .pause                  = mirror_pause,
+    .attached_aio_context   = mirror_attached_aio_context,
 };
 
 static void mirror_start_job(BlockDriverState *bs, BlockDriverState *target,
-- 
2.5.5