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 E6E4FC2BA2B for ; Sat, 11 Apr 2020 12:28:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BC8F520644 for ; Sat, 11 Apr 2020 12:28:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586608092; bh=Pa5+l78f/hLPIgJYaiYO+xjtCaCaOUnntR7EXklcnmw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=Q5Ba/6k19YlJnq6LYJRg+lbZQqPWK9qt37E1PimiVRoIi20t3udFUe86nYqhEtuZQ I5szzYkYMR8zdbnID4wp5iKuY0ICUhPY5fppcPNP6Cy5ZHdosvYnSEp2Et5qPD7Brj OG1WpNXnuAN1lIhnqH5T1KEMjuGrwXoz+SPmUI4I= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727624AbgDKMNI (ORCPT ); Sat, 11 Apr 2020 08:13:08 -0400 Received: from mail.kernel.org ([198.145.29.99]:45932 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727608AbgDKMNH (ORCPT ); Sat, 11 Apr 2020 08:13:07 -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 BACAC215A4; Sat, 11 Apr 2020 12:13:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586607187; bh=Pa5+l78f/hLPIgJYaiYO+xjtCaCaOUnntR7EXklcnmw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Ue/xMp0VupTqokbSEO4fth65CC8/QOpDytnPLv1u8i+Mfv13xDFbf38AKtax6dsNi qySAIEALpLYOdBwpLJ7ZETPvyOfgjf27Bb60K5gkmnjiMF+5PLNdX7sFm9yS7vhEO1 iKLfi0jTdQxEZNEO0N8X/uwaBL82DsbP4iJRLPz4= 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 4.14 10/38] blk-mq: Allow blocking queue tag iter callbacks Date: Sat, 11 Apr 2020 14:08:54 +0200 Message-Id: <20200411115439.016686728@linuxfoundation.org> X-Mailer: git-send-email 2.26.0 In-Reply-To: <20200411115437.795556138@linuxfoundation.org> References: <20200411115437.795556138@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@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 @@ -336,16 +336,11 @@ 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; @@ -361,7 +356,7 @@ 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 int bt_alloc(struct sbitmap_queue *bt, unsigned int depth,