From patchwork Mon May 18 17:36:37 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 225547 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 3E1DBC433E1 for ; Mon, 18 May 2020 18:30:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 16FC62065F for ; Mon, 18 May 2020 18:30:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589826640; bh=tBs33K+uNGXDzZgMYrAIoeato9mMKDEaIncgrf6We24=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=Q36IM32aV4L+8sFNkFAG+FKRmHHlzqhowIkRxrei8IkEgOoLRWxV0ijEus1QJNDU8 g4WRRyzYI7Vh8vz75YgVzTD9F5gCsGY3o7xZlR6134C9o6aF8GpBWiQNrHCnudms8S NlfqIVfPBn93KhCBtDkzxmwNtfaqy4CF08t1q/yM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728731AbgERSaf (ORCPT ); Mon, 18 May 2020 14:30:35 -0400 Received: from mail.kernel.org ([198.145.29.99]:36624 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729139AbgERRkp (ORCPT ); Mon, 18 May 2020 13:40:45 -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 E193020657; Mon, 18 May 2020 17:40:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589823645; bh=tBs33K+uNGXDzZgMYrAIoeato9mMKDEaIncgrf6We24=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=V2GVlOLAyy383m3BIlrg/LnEiRLL6weAFmMb1BPopgoEkZv2fofhU5S98HGlBeTq/ sbMN6iOlWpHZDkFhars24fVhV+/5IPpEvVCKYtRkxt58wxxUFgNnh/dB0jqeTvcSNC uGw+l4EY5zGymPFinUFFLHO0ucAp8Q6F4phaidhE= 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 4.4 66/86] blk-mq: Allow blocking queue tag iter callbacks Date: Mon, 18 May 2020 19:36:37 +0200 Message-Id: <20200518173503.689982128@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 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 | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-) --- a/block/blk-mq-tag.c +++ b/block/blk-mq-tag.c @@ -484,11 +484,8 @@ void blk_mq_queue_tag_busy_iter(struct r /* * Avoid potential races with things like queue removal. */ - 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; @@ -505,7 +502,7 @@ 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(); + blk_queue_exit(q); } static unsigned int bt_unused_tags(struct blk_mq_bitmap_tags *bt)