This patch fixes one issue reported by Kent, which can be triggered in bcachefs over sata disk. Actually it is a generic issue in block flush vs. blk-tag. Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx> Reported-by: Kent Overstreet <kent.overstreet@xxxxxxxxx> Signed-off-by: Ming Lei <tom.leiming@xxxxxxxxx> --- block/blk-flush.c | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+) diff --git a/block/blk-flush.c b/block/blk-flush.c index 6a14b68b9135..3c882cbc7541 100644 --- a/block/blk-flush.c +++ b/block/blk-flush.c @@ -343,6 +343,34 @@ static void flush_data_end_io(struct request *rq, int error) struct blk_flush_queue *fq = blk_get_flush_queue(q, NULL); /* + * Updating q->in_flight[] here for making this tag usable + * early. Because in blk_queue_start_tag(), + * q->in_flight[BLK_RW_ASYNC] is used to limit async I/O and + * reserve tags for sync I/O. + * + * More importantly this way can avoid the following I/O + * deadlock: + * + * - suppose there are 40 fua requests comming to flush queue + * and queue depth is 31 + * - 30 rqs are scheduled then blk_queue_start_tag() can't alloc + * tag for async I/O any more + * - all the 30 rqs are completed before FLUSH_PENDING_TIMEOUT + * and flush_data_end_io() is called + * - the other rqs still can't go ahead if not updating + * q->in_flight[BLK_RW_ASYNC] here, meantime these rqs + * are held in flush data queue and make no progress of + * handling post flush rq + * - only after the post flush rq is handled, all these rqs + * can be completed + */ + + elv_completed_request(q, rq); + + /* for avoiding double accounting */ + rq->cmd_flags &= ~REQ_STARTED; + + /* * After populating an empty queue, kick it to avoid stall. Read * the comment in flush_end_io(). */ -- 2.7.4 -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
