[ Upstream commit b554db147feea39617b533ab6bca247c91c6198a ]
We discovered a problem in newer kernels where a disconnect of a NBD device while the flush request was pending would result in a hang. This is because the blk mq timeout handler does
if (!refcount_inc_not_zero(&rq->ref)) return true;
to determine if it's ok to run the timeout handler for the request. Flush_rq's don't have a ref count set, so we'd skip running the timeout handler for this request and it would just sit there in limbo forever.
Fix this by always setting the refcount of any request going through blk_init_rq() to 1. I tested this with a nbd-server that dropped flush requests to verify that it hung, and then tested with this patch to verify I got the timeout as expected and the error handling kicked in. Thanks,
Signed-off-by: Josef Bacik josef@toxicpanda.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- block/blk-core.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/block/blk-core.c b/block/blk-core.c index 682bc561b77b..9ca703bcfe3b 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -198,6 +198,7 @@ void blk_rq_init(struct request_queue *q, struct request *rq) rq->internal_tag = -1; rq->start_time_ns = ktime_get_ns(); rq->part = NULL; + refcount_set(&rq->ref, 1); } EXPORT_SYMBOL(blk_rq_init);