block: wait_for_overlapping_requests() deadlock detection
Debugging a reentrant request deadlock was fun but in the future we need
a quick and obvious way of detecting such bugs. Add an assert that
checks we are not about to deadlock when waiting for another request.
Suggested-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/block.c b/block.c
index ecc5b44..50ce2be 100644
--- a/block.c
+++ b/block.c
@@ -1099,6 +1099,7 @@
int nb_sectors;
bool is_write;
QLIST_ENTRY(BdrvTrackedRequest) list;
+ Coroutine *co; /* owner, used for deadlock detection */
CoQueue wait_queue; /* coroutines blocked on this request */
};
@@ -1126,6 +1127,7 @@
.sector_num = sector_num,
.nb_sectors = nb_sectors,
.is_write = is_write,
+ .co = qemu_coroutine_self(),
};
qemu_co_queue_init(&req->wait_queue);
@@ -1189,6 +1191,12 @@
QLIST_FOREACH(req, &bs->tracked_requests, list) {
if (tracked_request_overlaps(req, cluster_sector_num,
cluster_nb_sectors)) {
+ /* Hitting this means there was a reentrant request, for
+ * example, a block driver issuing nested requests. This must
+ * never happen since it means deadlock.
+ */
+ assert(qemu_coroutine_self() != req->co);
+
qemu_co_queue_wait(&req->wait_queue);
retry = true;
break;