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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7FCD3C001E0 for ; Mon, 31 Jul 2023 14:07:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233020AbjGaOHF (ORCPT ); Mon, 31 Jul 2023 10:07:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54474 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233215AbjGaOGb (ORCPT ); Mon, 31 Jul 2023 10:06:31 -0400 Received: from out-118.mta0.migadu.com (out-118.mta0.migadu.com [91.218.175.118]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1FDD61BE9 for ; Mon, 31 Jul 2023 07:03:08 -0700 (PDT) Message-ID: <0ee17228-4938-6ab7-3fc4-f83a81cbed8f@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1690812186; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=r0Xei3Zm1daHRy1itcMrY96v4n4keK9eRkuLyVzagVw=; b=TEMvXNrOedWtUAvNhNxUCn63M0TflhKOVoQv6pbBqSyv4ssJuB04UMHaTB2RGgcjK6dvs9 csYU2Dyo2TSJzhu0xhGLALuExTFl5Y6sXE1N5ONmqiEcD4pkE9EgJO0k35jJgirJZJ69H4 PvFk+fScf/B6w8QQCnl5oR3rfPd1anM= Date: Mon, 31 Jul 2023 22:02:39 +0800 MIME-Version: 1.0 Subject: Re: [PATCH v2 1/4] blk-flush: flush_rq should inherit first_rq's cmd_flags Content-Language: en-US To: Christoph Hellwig , hare@suse.de Cc: axboe@kernel.dk, ming.lei@redhat.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, zhouchengming@bytedance.com References: <20230725130102.3030032-1-chengming.zhou@linux.dev> <20230725130102.3030032-2-chengming.zhou@linux.dev> <20230731060957.GA30409@lst.de> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Chengming Zhou In-Reply-To: <20230731060957.GA30409@lst.de> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2023/7/31 14:09, Christoph Hellwig wrote: > On Tue, Jul 25, 2023 at 09:00:59PM +0800, chengming.zhou@linux.dev wrote: >> From: Chengming Zhou >> >> The cmd_flags in blk_kick_flush() should inherit the original request's >> cmd_flags, but the current code looks buggy to me: > > Should it? I know the code is kinda trying to do it, but does it really > make sense? Adding Hannes who originally added this inheritance and > discussing the details below: I'm not sure, actually I don't get what the current code is doing... Hope Hannes could provide some details. blk_flush_complete_seq(rq) -> blk_kick_flush(rq->cmd_flags) flush_rq will use the cmd_flags of request which just complete a sequence, there are three cases: 1. blk_insert_flush(rq): rq is pending, wait for flush 2. flush_end_io(flush_rq): rq flush seq done 3. mq_flush_data_end_io(rq): rq data seq done Only in the 1st case, the rq is the pending request that wait for flush_rq. In the 2nd and 3rd cases, the rq has nothing to do with the next flush_rq? So it's more reasonable for flush_rq to use its pending first_rq's cmd_flags? > >> flush_rq->cmd_flags = REQ_OP_FLUSH | REQ_PREFLUSH; >> - flush_rq->cmd_flags |= (flags & REQ_DRV) | (flags & REQ_FAILFAST_MASK); >> + flush_rq->cmd_flags |= (first_rq->cmd_flags & REQ_DRV) | >> + (first_rq->cmd_flags & REQ_FAILFAST_MASK); > > Two cases here: > > 1) REQ_FAILFAST_MASK: I don't think this is actually set on flush request > currently, and even if it was applying it to the flush that serves more > than a single originating command seems wrong to me. > 2) REQ_DRV is only set by drivers that have seen a bio. For dm this > is used as REQ_DM_POLL_LIST which should never be set for a flush/fua > request. For nvme-mpath it is REQ_NVME_MPATH, which is set in the > bio based driver and used for decision making in the I/O completion > handler. So I guess this one actually does need to get passed > through. > The commit 84fca1b0c461 ("block: pass failfast and driver-specific flags to flush requests") says: If flush requests are being sent to the device we need to inherit the failfast and driver-specific flags, too, otherwise I/O will fail. 1) REQ_FAILFAST_MASK: agree, shouldn't set to the flush_rq I think? 2) REQ_DRV: I don't get why this flag not set would cause I/O fail? Thanks!