mirror: fix early wake from sleep due to aio

The mirror blockjob coroutine rate-limits itself by sleeping.  The
coroutine also performs I/O asynchronously so it's important that the
aio callback doesn't wake the coroutine early as that breaks
rate-limiting.

Reported-by: Joaquim Barrera <jbarrera@ac.upc.edu>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

diff --git a/block/mirror.c b/block/mirror.c
index adb09cf4ab20ed6691f7d9801e8e09ce639b2664..0ef41f999e405b295df1ee02666a4bcddf06200e 100644 (file)
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -98,7 +98,14 @@ static void mirror_iteration_done(MirrorOp *op, int ret)
 
     qemu_iovec_destroy(&op->qiov);
     g_slice_free(MirrorOp, op);
-    qemu_coroutine_enter(s->common.co, NULL);
+
+    /* Enter coroutine when it is not sleeping.  The coroutine sleeps to
+     * rate-limit itself.  The coroutine will eventually resume since there is
+     * a sleep timeout so don't wake it early.
+     */
+    if (s->common.busy) {
+        qemu_coroutine_enter(s->common.co, NULL);
+    }
 }
 
 static void mirror_write_complete(void *opaque, int ret)