From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:60805 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753437AbdAZTsd (ORCPT ); Thu, 26 Jan 2017 14:48:33 -0500 From: Jens Axboe To: CC: , , , , , Jens Axboe Subject: [PATCH 2/5] blk-mq: fix potential race in queue restart and driver tag allocation Date: Thu, 26 Jan 2017 12:48:15 -0700 Message-ID: <1485460098-16608-3-git-send-email-axboe@fb.com> In-Reply-To: <1485460098-16608-1-git-send-email-axboe@fb.com> References: <1485460098-16608-1-git-send-email-axboe@fb.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-block-owner@vger.kernel.org List-Id: linux-block@vger.kernel.org Once we mark the queue as needing a restart, re-check if we can get a driver tag. This fixes a theoretical issue where the needed IO completes _after_ blk_mq_get_driver_tag() fails, but before we manage to set the restart bit. Signed-off-by: Jens Axboe --- block/blk-mq.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/block/blk-mq.c b/block/blk-mq.c index 223b9b080820..8041ad330289 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -928,7 +928,16 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list) if (!blk_mq_get_driver_tag(rq, &hctx, false)) { if (!queued && reorder_tags_to_front(list)) continue; + + /* + * We failed getting a driver tag. Mark the queue(s) + * as needing a restart. Retry getting a tag again, + * in case the needed IO completed right before we + * marked the queue as needing a restart. + */ blk_mq_sched_mark_restart(hctx); + if (!blk_mq_get_driver_tag(rq, &hctx, false)) + break; break; } list_del_init(&rq->queuelist); -- 2.7.4