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 <kw...@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefa...@linux.vnet.ibm.com>
---
block.c | 8 ++++++++
1 files changed, 8 insertions(+), 0 deletions(-)
diff --git a/block.c b/block.c
index 4310eb5..37a96f3 100644
--- a/block.c
+++ b/block.c
@@ -1099,6 +1099,7 @@ struct BdrvTrackedRequest {
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 @@ static void tracked_request_begin(BdrvTrackedRequest *req,
.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 @@ static void coroutine_fn
wait_for_overlapping_requests(BlockDriverState *bs,
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;
--
1.7.7.3
