Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933799AbcJZI6r (ORCPT ); Wed, 26 Oct 2016 04:58:47 -0400 Received: from mail-pf0-f175.google.com ([209.85.192.175]:34053 "EHLO mail-pf0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756895AbcJZI55 (ORCPT ); Wed, 26 Oct 2016 04:57:57 -0400 From: Ming Lei To: Jens Axboe , linux-kernel@vger.kernel.org Cc: linux-block@vger.kernel.org, Christoph Hellwig , Kent Overstreet , Ming Lei , Jens Axboe Subject: [PATCH] block: flush: fix IO hang in case of flood fua req Date: Wed, 26 Oct 2016 16:57:15 +0800 Message-Id: <1477472235-22845-1-git-send-email-tom.leiming@gmail.com> X-Mailer: git-send-email 2.7.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1804 Lines: 52 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 Reported-by: Kent Overstreet Signed-off-by: Ming Lei --- 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