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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 34818C433E1 for ; Mon, 18 May 2020 17:41:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 16E0520657 for ; Mon, 18 May 2020 17:41:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589823661; bh=k+sP1Ye2sq++ijswRFnpLTlJM38933ANkE+pDkrZzCA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=rr3fML/7KaJ+U4LwAs0PUEel5Amj7BToIbd+2TYHoVuPA25OBNn5D0IttzNTSA4jX 27FhdVDSU1o+diRdCWLI36RRS6ul8xQnaDzVzDMhsZnLL8fo0391XWFgG/koNe9A7P 7ZBjh7Prl8gtXCdU6izqC1LOsRt80dfPVYW//0i4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729192AbgERRlA (ORCPT ); Mon, 18 May 2020 13:41:00 -0400 Received: from mail.kernel.org ([198.145.29.99]:36538 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729134AbgERRkn (ORCPT ); Mon, 18 May 2020 13:40:43 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 797E720835; Mon, 18 May 2020 17:40:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589823642; bh=k+sP1Ye2sq++ijswRFnpLTlJM38933ANkE+pDkrZzCA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=2XvQncyKPmMhME1yW8nUws4HXCN0oGnQKCsk7cdxcjYE/SQ5Tgt3xT4WayYxBbYVf HDOW39Gg0b5/NZWtl6omKJJ46h+EoN3vDZW9/M1qXF1IaOCNKZAe5V3QYfsfRW0ncx tBeMnrNOpVn1oC9jm6phr7zREY3or2GIHjPRr+oc= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Jianchao Wang , Ming Lei , Jens Axboe , Giuliano Procida Subject: [PATCH 4.4 65/86] blk-mq: sync the update nr_hw_queues with blk_mq_queue_tag_busy_iter Date: Mon, 18 May 2020 19:36:36 +0200 Message-Id: <20200518173503.473464673@linuxfoundation.org> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200518173450.254571947@linuxfoundation.org> References: <20200518173450.254571947@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Jianchao Wang commit f5bbbbe4d63577026f908a809f22f5fd5a90ea1f upstream. For blk-mq, part_in_flight/rw will invoke blk_mq_in_flight/rw to account the inflight requests. It will access the queue_hw_ctx and nr_hw_queues w/o any protection. When updating nr_hw_queues and blk_mq_in_flight/rw occur concurrently, panic comes up. Before update nr_hw_queues, the q will be frozen. So we could use q_usage_counter to avoid the race. percpu_ref_is_zero is used here so that we will not miss any in-flight request. The access to nr_hw_queues and queue_hw_ctx in blk_mq_queue_tag_busy_iter are under rcu critical section, __blk_mq_update_nr_hw_queues could use synchronize_rcu to ensure the zeroed q_usage_counter to be globally visible. -------------- NOTE: Back-ported to 4.4.y. The upstream commit was intended to prevent concurrent manipulation of nr_hw_queues and iteration over queues. The former doesn't happen in this in 4.4.7 (as __blk_mq_update_nr_hw_queues doesn't exist). The extra locking is also buggy in this commit but fixed in a follow-up. It may protect against other concurrent accesses such as queue removal by synchronising RCU locking around q_usage_counter. -------------- Signed-off-by: Jianchao Wang Reviewed-by: Ming Lei Signed-off-by: Jens Axboe Signed-off-by: Giuliano Procida Signed-off-by: Greg Kroah-Hartman --- block/blk-mq-tag.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) --- a/block/blk-mq-tag.c +++ b/block/blk-mq-tag.c @@ -481,6 +481,14 @@ void blk_mq_queue_tag_busy_iter(struct r struct blk_mq_hw_ctx *hctx; int i; + /* + * Avoid potential races with things like queue removal. + */ + rcu_read_lock(); + if (percpu_ref_is_zero(&q->q_usage_counter)) { + rcu_read_unlock(); + return; + } queue_for_each_hw_ctx(q, hctx, i) { struct blk_mq_tags *tags = hctx->tags; @@ -497,7 +505,7 @@ void blk_mq_queue_tag_busy_iter(struct r bt_for_each(hctx, &tags->bitmap_tags, tags->nr_reserved_tags, fn, priv, false); } - + rcu_read_unlock(); } static unsigned int bt_unused_tags(struct blk_mq_bitmap_tags *bt)