[Qemu-devel] [PATCH] block/mirror: fix fail to cancel when VM has heavy BLK IO

[Liang Li <liliangleo@didichuxing.com>]

We found that when doing drive mirror to a low speed shared storage,
if there was heavy BLK IO write workload in VM after the 'ready' event,
drive mirror block job can't be canceled immediately, it would keep
running until the heavy BLK IO workload stopped in the VM. This patch
fixed this issue.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Jeff Cody <jcody@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Max Reitz <mreitz@redhat.com>
Signed-off-by: Huaitong Han <hanhuaitong@didichuxing.com>
Signed-off-by: Liang Li <liliangleo@didichuxing.com>
---
 block/mirror.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/block/mirror.c b/block/mirror.c
index c9badc1..3bc49a5 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -869,11 +869,9 @@ static void coroutine_fn mirror_run(void *opaque)
 
         ret = 0;
         trace_mirror_before_sleep(s, cnt, s->synced, delay_ns);
-        if (!s->synced) {
-            block_job_sleep_ns(&s->common, delay_ns);
-            if (block_job_is_cancelled(&s->common)) {
-                break;
-            }
+
+        if (block_job_is_cancelled(&s->common)) {
+            break;
         } else if (!should_complete) {
             delay_ns = (s->in_flight == 0 && cnt == 0 ? SLICE_TIME : 0);
             block_job_sleep_ns(&s->common, delay_ns);
@@ -887,7 +885,7 @@ immediate_exit:
          * or it was cancelled prematurely so that we do not guarantee that
          * the target is a copy of the source.
          */
-        assert(ret < 0 || (!s->synced && block_job_is_cancelled(&s->common)));
+        assert(ret < 0 || block_job_is_cancelled(&s->common));
         assert(need_drain);
         mirror_wait_for_all_io(s);
     }
-- 
1.8.3.1