From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [PATCH 4/5] dm: implement REQ_FLUSH/FUA support for request-based dm Date: Mon, 30 Aug 2010 17:07:46 +0200 Message-ID: <4C7BC942.7070703@kernel.org> References: <1283162296-13650-1-git-send-email-tj@kernel.org> <1283162296-13650-5-git-send-email-tj@kernel.org> <20100830132836.GB5283@redhat.com> <4C7BB932.1070405@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4C7BB932.1070405@kernel.org> Sender: linux-kernel-owner@vger.kernel.org To: Mike Snitzer Cc: jaxboe@fusionio.com, k-ueda@ct.jp.nec.com, j-nomura@ce.jp.nec.com, jamie@shareable.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-raid@vger.kernel.org, hch@lst.de List-Id: linux-raid.ids On 08/30/2010 03:59 PM, Tejun Heo wrote: > Ah... that's probably from "if (!elv_queue_empty(q))" check below, > flushes are on a separate queue but I forgot to update > elv_queue_empty() to check the flush queue. elv_queue_empty() can > return %true spuriously in which case the queue won't be plugged and > restarted later leading to queue hang. I'll fix elv_queue_empty(). I think I was too quick to blame elv_queue_empty(). Can you please test whether the following patch fixes the hang? Thanks. --- block/blk-flush.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) Index: block/block/blk-flush.c =================================================================== --- block.orig/block/blk-flush.c +++ block/block/blk-flush.c @@ -28,7 +28,8 @@ unsigned blk_flush_cur_seq(struct reques } static struct request *blk_flush_complete_seq(struct request_queue *q, - unsigned seq, int error) + unsigned seq, int error, + bool from_end_io) { struct request *next_rq = NULL; @@ -51,6 +52,13 @@ static struct request *blk_flush_complet if (!list_empty(&q->pending_flushes)) { next_rq = list_entry_rq(q->pending_flushes.next); list_move(&next_rq->queuelist, &q->queue_head); + /* + * Moving a request silently to queue_head may + * stall the queue, kick the queue if we + * aren't in the issue path already. + */ + if (from_end_io) + __blk_run_queue(q); } } return next_rq; @@ -59,19 +67,19 @@ static struct request *blk_flush_complet static void pre_flush_end_io(struct request *rq, int error) { elv_completed_request(rq->q, rq); - blk_flush_complete_seq(rq->q, QUEUE_FSEQ_PREFLUSH, error); + blk_flush_complete_seq(rq->q, QUEUE_FSEQ_PREFLUSH, error, true); } static void flush_data_end_io(struct request *rq, int error) { elv_completed_request(rq->q, rq); - blk_flush_complete_seq(rq->q, QUEUE_FSEQ_DATA, error); + blk_flush_complete_seq(rq->q, QUEUE_FSEQ_DATA, error, true); } static void post_flush_end_io(struct request *rq, int error) { elv_completed_request(rq->q, rq); - blk_flush_complete_seq(rq->q, QUEUE_FSEQ_POSTFLUSH, error); + blk_flush_complete_seq(rq->q, QUEUE_FSEQ_POSTFLUSH, error, true); } static void init_flush_request(struct request *rq, struct gendisk *disk) @@ -165,7 +173,7 @@ struct request *blk_do_flush(struct requ skip |= QUEUE_FSEQ_DATA; if (!do_postflush) skip |= QUEUE_FSEQ_POSTFLUSH; - return blk_flush_complete_seq(q, skip, 0); + return blk_flush_complete_seq(q, skip, 0, false); } static void bio_end_flush(struct bio *bio, int err)