block/mirror: fix active mirror dead-lock in mirror_wait_on_conflicts
It's possible that requests start to wait each other in
mirror_wait_on_conflicts(). To avoid it let's use same technique as in
block/io.c in bdrv_wait_serialising_requests_locked() /
bdrv_find_conflicting_request(): don't wait on intersecting request if
it is already waiting for some other request.
For details of the dead-lock look at testIntersectingActiveIO()
test-case which we actually fixing now.
Fixes: d06107ade0ce74dc39739bac80de84b51ec18546
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20210702211636.228981-4-vsementsov@virtuozzo.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/block/mirror.c b/block/mirror.c
index ad6aac2..98fc66e 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -107,6 +107,7 @@
bool is_in_flight;
CoQueue waiting_requests;
Coroutine *co;
+ MirrorOp *waiting_for_op;
QTAILQ_ENTRY(MirrorOp) next;
};
@@ -159,7 +160,18 @@
if (ranges_overlap(self_start_chunk, self_nb_chunks,
op_start_chunk, op_nb_chunks))
{
+ /*
+ * If the operation is already (indirectly) waiting for us, or
+ * will wait for us as soon as it wakes up, then just go on
+ * (instead of producing a deadlock in the former case).
+ */
+ if (op->waiting_for_op) {
+ continue;
+ }
+
+ self->waiting_for_op = op;
qemu_co_queue_wait(&op->waiting_requests, NULL);
+ self->waiting_for_op = NULL;
break;
}
}
