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,URIBL_BLOCKED,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 EB7B0C2BA2B for ; Sat, 11 Apr 2020 12:12:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C45C021841 for ; Sat, 11 Apr 2020 12:12:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586607167; bh=du34FuSZ/93isxJl6ceSMUx6+clIj0/Chgs4FwB6Bf0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=02cVSaiKRK9U350P/3USRa7O8nB0hkR6JWq0jdt02BdhGCxvSEb2LHMQ5MsoXrXQ+ qG3z7oyH4khXSevMufqf51fdJmunXWM8JNYLQzGOEAX5tw1WZXvMksAbj1nlmZa9VH hv2Dx1NKjdU8gNzd4dahoeHr6OjntaygrW6EyTEY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727436AbgDKMMq (ORCPT ); Sat, 11 Apr 2020 08:12:46 -0400 Received: from mail.kernel.org ([198.145.29.99]:45422 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727369AbgDKMMm (ORCPT ); Sat, 11 Apr 2020 08:12:42 -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 93B93216FD; Sat, 11 Apr 2020 12:12:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586607163; bh=du34FuSZ/93isxJl6ceSMUx6+clIj0/Chgs4FwB6Bf0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=RBup08jiylVsZc9KThzn2w7/3P6G8qThfKrirvyn/E/voRiJaxUU+iGjSVYpqq55h Kaw0nh/SfA2/+vjDTvLBp0jlufxetizMZ2fbjJJfu9gJEa2wHjAM8Ihyoc1J6Xivsp Ohopm0LURrwfAOjmmliilxRR+ZbAmnegRWFeHoeA= 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 4.9 09/32] blk-mq: sync the update nr_hw_queues with blk_mq_queue_tag_busy_iter Date: Sat, 11 Apr 2020 14:08:48 +0200 Message-Id: <20200411115419.710747345@linuxfoundation.org> X-Mailer: git-send-email 2.26.0 In-Reply-To: <20200411115418.455500023@linuxfoundation.org> References: <20200411115418.455500023@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. Signed-off-by: Jianchao Wang Reviewed-by: Ming Lei Signed-off-by: Jens Axboe Cc: Giuliano Procida Signed-off-by: Greg Kroah-Hartman --- block/blk-mq-tag.c | 14 +++++++++++++- block/blk-mq.c | 4 ++++ 2 files changed, 17 insertions(+), 1 deletion(-) --- a/block/blk-mq-tag.c +++ b/block/blk-mq-tag.c @@ -336,6 +336,18 @@ void blk_mq_queue_tag_busy_iter(struct r struct blk_mq_hw_ctx *hctx; int i; + /* + * __blk_mq_update_nr_hw_queues will update the nr_hw_queues and + * queue_hw_ctx after freeze the queue. So we could use q_usage_counter + * to avoid race with it. __blk_mq_update_nr_hw_queues will users + * synchronize_rcu to ensure all of the users go out of the critical + * section below and see zeroed q_usage_counter. + */ + 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; @@ -351,7 +363,7 @@ void blk_mq_queue_tag_busy_iter(struct r bt_for_each(hctx, &tags->breserved_tags, fn, priv, true); bt_for_each(hctx, &tags->bitmap_tags, fn, priv, false); } - + rcu_read_unlock(); } static unsigned int bt_unused_tags(const struct sbitmap_queue *bt) --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2346,6 +2346,10 @@ void blk_mq_update_nr_hw_queues(struct b list_for_each_entry(q, &set->tag_list, tag_set_list) blk_mq_unfreeze_queue(q); + /* + * Sync with blk_mq_queue_tag_busy_iter. + */ + synchronize_rcu(); } EXPORT_SYMBOL_GPL(blk_mq_update_nr_hw_queues);