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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EA48AC433EF for ; Thu, 11 Nov 2021 08:56:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D242561884 for ; Thu, 11 Nov 2021 08:56:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229956AbhKKI7l (ORCPT ); Thu, 11 Nov 2021 03:59:41 -0500 Received: from verein.lst.de ([213.95.11.211]:57489 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229533AbhKKI7l (ORCPT ); Thu, 11 Nov 2021 03:59:41 -0500 Received: by verein.lst.de (Postfix, from userid 2407) id 9C9AE67373; Thu, 11 Nov 2021 09:56:50 +0100 (CET) Date: Thu, 11 Nov 2021 09:56:50 +0100 From: Christoph Hellwig To: Ming Lei Cc: Jens Axboe , linux-block@vger.kernel.org, Christoph Hellwig Subject: Re: [PATCH 1/2] blk-mq: don't grab ->q_usage_counter in blk_mq_sched_bio_merge Message-ID: <20211111085650.GA476@lst.de> References: <20211111085134.345235-1-ming.lei@redhat.com> <20211111085134.345235-2-ming.lei@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211111085134.345235-2-ming.lei@redhat.com> User-Agent: Mutt/1.5.17 (2007-11-01) Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Thu, Nov 11, 2021 at 04:51:33PM +0800, Ming Lei wrote: > blk_mq_sched_bio_merge is only called from blk-mq.c:blk_attempt_bio_merge(), > which is called when queue usage counter is grabbed already: > > 1) blk_mq_get_new_requests() > > 2) blk_mq_get_request() > - cached request in current plug owns one queue usage counter > > So don't grab ->q_usage_counter in blk_mq_sched_bio_merge(), and more > importantly this nest way causes hang in blk_mq_freeze_queue_wait(). Looks good, Reviewed-by: Christoph Hellwig