Re: [PATCH 4/5] dm: implement REQ_FLUSH/FUA support for request-based dm
From: Tejun Heo <tj@kernel.org>
Date: 2010-08-31 10:29:59
Also in:
dm-devel, linux-fsdevel, lkml
On 08/30/2010 11:28 PM, Mike Snitzer wrote:
On Mon, Aug 30 2010 at 3:08pm -0400, Mike Snitzer [off-list ref] wrote:quoted
On Mon, Aug 30 2010 at 11:07am -0400, Tejun Heo [off-list ref] wrote:quoted
On 08/30/2010 03:59 PM, Tejun Heo wrote:quoted
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?It does, thanks!Hmm, but unfortunately I was too quick to say the patch fixed the hang. It is much more rare, but I can still get a hang. I just got the following running vgcreate against an DM mpath (rq-based) device:
Can you please try this one instead? Thanks. --- block/blk-flush.c | 22 +++++++++++++++++++--- 1 file changed, 19 insertions(+), 3 deletions(-) Index: block/block/blk-flush.c ===================================================================
--- block.orig/block/blk-flush.c
+++ block/block/blk-flush.c@@ -56,22 +56,38 @@ static struct request *blk_flush_complet return next_rq; } +static void blk_flush_complete_seq_end_io(struct request_queue *q, + unsigned seq, int error) +{ + bool was_empty = elv_queue_empty(q); + struct request *next_rq; + + next_rq = blk_flush_complete_seq(q, seq, error); + + /* + * Moving a request silently to empty queue_head may stall the + * queue. Kick the queue in those cases. + */ + if (next_rq && was_empty) + __blk_run_queue(q); +} + 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_end_io(rq->q, QUEUE_FSEQ_PREFLUSH, error); } 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_end_io(rq->q, QUEUE_FSEQ_DATA, error); } 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_end_io(rq->q, QUEUE_FSEQ_POSTFLUSH, error); } static void init_flush_request(struct request *rq, struct gendisk *disk)
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tejun