From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 053E0C43218 for ; Sun, 28 Apr 2019 08:14:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CEA962075D for ; Sun, 28 Apr 2019 08:14:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726466AbfD1IOV (ORCPT ); Sun, 28 Apr 2019 04:14:21 -0400 Received: from mx1.redhat.com ([209.132.183.28]:57874 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726488AbfD1IOV (ORCPT ); Sun, 28 Apr 2019 04:14:21 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id CF7E4C02938A; Sun, 28 Apr 2019 08:14:20 +0000 (UTC) Received: from localhost (ovpn-8-32.pek2.redhat.com [10.72.8.32]) by smtp.corp.redhat.com (Postfix) with ESMTP id C426A620DF; Sun, 28 Apr 2019 08:14:17 +0000 (UTC) From: Ming Lei To: Jens Axboe Cc: linux-block@vger.kernel.org, Ming Lei , Dongli Zhang , James Smart , Bart Van Assche , linux-scsi@vger.kernel.org, "Martin K . Petersen" , Christoph Hellwig , "James E . J . Bottomley" Subject: [PATCH V8 1/7] blk-mq: grab .q_usage_counter when queuing request from plug code path Date: Sun, 28 Apr 2019 16:14:02 +0800 Message-Id: <20190428081408.27331-2-ming.lei@redhat.com> In-Reply-To: <20190428081408.27331-1-ming.lei@redhat.com> References: <20190428081408.27331-1-ming.lei@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Sun, 28 Apr 2019 08:14:20 +0000 (UTC) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Just like aio/io_uring, we need to grab 2 refcount for queuing one request, one is for submission, another is for completion. If the request isn't queued from plug code path, the refcount grabbed in generic_make_request() serves for submission. In theroy, this refcount should have been released after the sumission(async run queue) is done. blk_freeze_queue() works with blk_sync_queue() together for avoiding race between cleanup queue and IO submission, given async run queue activities are canceled because hctx->run_work is scheduled with the refcount held, so it is fine to not hold the refcount when running the run queue work function for dispatch IO. However, if request is staggered into plug list, and finally queued from plug code path, the refcount in submission side is actually missed. And we may start to run queue after queue is removed because the queue's kobject refcount isn't guaranteed to be grabbed in flushing plug list context, then kernel oops is triggered, see the following race: blk_mq_flush_plug_list(): blk_mq_sched_insert_requests() insert requests to sw queue or scheduler queue blk_mq_run_hw_queue Because of concurrent run queue, all requests inserted above may be completed before calling the above blk_mq_run_hw_queue. Then queue can be freed during the above blk_mq_run_hw_queue(). Fixes the issue by grab .q_usage_counter before calling blk_mq_sched_insert_requests() in blk_mq_flush_plug_list(). This way is safe because the queue is absolutely alive before inserting request. Cc: Dongli Zhang Cc: James Smart Cc: Bart Van Assche Cc: linux-scsi@vger.kernel.org, Cc: Martin K . Petersen , Cc: Christoph Hellwig , Cc: James E . J . Bottomley , Reviewed-by: Bart Van Assche Reviewed-by: Johannes Thumshirn Reviewed-by: Hannes Reinecke Tested-by: James Smart Signed-off-by: Ming Lei --- block/blk-mq-sched.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c index aa6bc5c02643..dfe83e7935d6 100644 --- a/block/blk-mq-sched.c +++ b/block/blk-mq-sched.c @@ -414,6 +414,13 @@ void blk_mq_sched_insert_requests(struct blk_mq_hw_ctx *hctx, { struct elevator_queue *e; + /* + * blk_mq_sched_insert_requests() is called from flush plug + * context only, and hold one usage counter to prevent queue + * from being released. + */ + percpu_ref_get(&hctx->queue->q_usage_counter); + e = hctx->queue->elevator; if (e && e->type->ops.insert_requests) e->type->ops.insert_requests(hctx, list, false); @@ -432,6 +439,8 @@ void blk_mq_sched_insert_requests(struct blk_mq_hw_ctx *hctx, } blk_mq_run_hw_queue(hctx, run_queue_async); + + percpu_ref_put(&hctx->queue->q_usage_counter); } static void blk_mq_sched_free_tags(struct blk_mq_tag_set *set, -- 2.9.5