| Message ID | 20190307213718.28017-1-josef@toxicpanda.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | block: init flush rq ref count to 1 | expand |
On 3/7/19 2:37 PM, Josef Bacik wrote: > 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, Looks good to me, thanks Josef.
diff --git a/block/blk-core.c b/block/blk-core.c index 6b78ec56a4f2..6107b27c14fb 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -116,6 +116,7 @@ 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);
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> --- block/blk-core.c | 1 + 1 file changed, 1 insertion(+)