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=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 AC8FCC2BB85 for ; Sat, 11 Apr 2020 12:11:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 894342166E for ; Sat, 11 Apr 2020 12:11:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586607117; bh=D9BT4LnQiZVTSEBlj7I5RanesxFX/AwNwPbKZ9CyOBQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=TGpneRhupMT9YWbVRCVAT/mihiX4qD3ocu8SlmHkPG7uvyr69iPIcAqMsbVsKRONz dkUBxPD/OU7loLazoVkEbgiPdLw/JZHV3SwOMf75tflp0OmLv+w7PXkbPGKMYi27Pe x8Fa/rRtY22SvbHP7V7bfLwEbyd+VDd/wNJyaf6Q= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727083AbgDKMLy (ORCPT ); Sat, 11 Apr 2020 08:11:54 -0400 Received: from mail.kernel.org ([198.145.29.99]:44016 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727045AbgDKMLs (ORCPT ); Sat, 11 Apr 2020 08:11:48 -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 C3AE220787; Sat, 11 Apr 2020 12:11:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586607107; bh=D9BT4LnQiZVTSEBlj7I5RanesxFX/AwNwPbKZ9CyOBQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=R1X1Aw+3Qa5Kxez0drEXdQ+dQ7rMJQl5QFJ/legVS29BTcXTVBJfRYTQRvaGD5HXN lqaWZHyJDBVhXxnC8fIPKoTlVdafOgXNRfBIG6RrtVa2KVCBoOG7H3x+WN/+8tSV0R nz+RDwsqwtX2mShCUcFVt7bo7hVviSLBH8c7LJ5I= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Jianchao Wang , Keith Busch , Jens Axboe , Giuliano Procida Subject: [PATCH 4.9 10/32] blk-mq: Allow blocking queue tag iter callbacks Date: Sat, 11 Apr 2020 14:08:49 +0200 Message-Id: <20200411115419.774992055@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: Keith Busch commit 530ca2c9bd6949c72c9b5cfc330cb3dbccaa3f5b upstream. A recent commit runs tag iterator callbacks under the rcu read lock, but existing callbacks do not satisfy the non-blocking requirement. The commit intended to prevent an iterator from accessing a queue that's being modified. This patch fixes the original issue by taking a queue reference instead of reading it, which allows callbacks to make blocking calls. Fixes: f5bbbbe4d6357 ("blk-mq: sync the update nr_hw_queues with blk_mq_queue_tag_busy_iter") Acked-by: Jianchao Wang Signed-off-by: Keith Busch Signed-off-by: Jens Axboe Signed-off-by: Giuliano Procida Signed-off-by: Greg Kroah-Hartman --- block/blk-mq-tag.c | 13 ++++--------- 1 file changed, 4 insertions(+), 9 deletions(-) --- a/block/blk-mq-tag.c +++ b/block/blk-mq-tag.c @@ -338,16 +338,11 @@ void blk_mq_queue_tag_busy_iter(struct r /* * __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. + * queue_hw_ctx after freeze the queue, so we use q_usage_counter + * to avoid race with it. */ - rcu_read_lock(); - if (percpu_ref_is_zero(&q->q_usage_counter)) { - rcu_read_unlock(); + if (!percpu_ref_tryget(&q->q_usage_counter)) return; - } queue_for_each_hw_ctx(q, hctx, i) { struct blk_mq_tags *tags = hctx->tags; @@ -363,7 +358,7 @@ 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(); + blk_queue_exit(q); } static unsigned int bt_unused_tags(const struct sbitmap_queue *bt)