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=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT 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 B457EC282C8 for ; Mon, 28 Jan 2019 17:18:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8A8E12082E for ; Mon, 28 Jan 2019 17:18:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731164AbfA1RSS (ORCPT ); Mon, 28 Jan 2019 12:18:18 -0500 Received: from mx1.redhat.com ([209.132.183.28]:41760 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731803AbfA1RSR (ORCPT ); Mon, 28 Jan 2019 12:18:17 -0500 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 65CC7792BA; Mon, 28 Jan 2019 17:18:16 +0000 (UTC) Received: from localhost (unknown [10.18.25.174]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C98E8422C; Mon, 28 Jan 2019 17:18:12 +0000 (UTC) Date: Mon, 28 Jan 2019 12:18:12 -0500 From: Mike Snitzer To: Greg KH Cc: bgurney@redhat.com, ming.lei@redhat.com, stable@vger.kernel.org, axboe@kernel.dk Subject: Re: FAILED: patch "[PATCH] dm: fix redundant IO accounting for bios that need splitting" failed to apply to 4.20-stable tree Message-ID: <20190128171811.GA22768@redhat.com> References: <154867983112385@kroah.com> <20190128153141.GA22326@redhat.com> <20190128160013.GA28714@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190128160013.GA28714@kroah.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Mon, 28 Jan 2019 17:18:16 +0000 (UTC) Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Mon, Jan 28 2019 at 11:00am -0500, Greg KH wrote: > On Mon, Jan 28, 2019 at 10:31:41AM -0500, Mike Snitzer wrote: > > On Mon, Jan 28 2019 at 7:50am -0500, > > gregkh@linuxfoundation.org wrote: > > > > > > > > The patch below does not apply to the 4.20-stable tree. > > > If someone wants it applied there, or to any other stable or longterm > > > tree, then please email the backport, including the original git commit > > > id to . > > > > > > thanks, > > > > > > greg k-h > > > > > > ------------------ original commit in Linus's tree ------------------ > > > > > > From a1e1cb72d96491277ede8d257ce6b48a381dd336 Mon Sep 17 00:00:00 2001 > > > From: Mike Snitzer > > > Date: Thu, 17 Jan 2019 10:48:01 -0500 > > > Subject: [PATCH] dm: fix redundant IO accounting for bios that need splitting > > > > > > The risk of redundant IO accounting was not taken into consideration > > > when commit 18a25da84354 ("dm: ensure bio submission follows a > > > depth-first tree walk") introduced IO splitting in terms of recursion > > > via generic_make_request(). > > > > > > Fix this by subtracting the split bio's payload from the IO stats that > > > were already accounted for by start_io_acct() upon dm_make_request() > > > entry. This repeat oscillation of the IO accounting, up then down, > > > isn't ideal but refactoring DM core's IO splitting to pre-split bios > > > _before_ they are accounted turned out to be an excessive amount of > > > change that will need a full development cycle to refine and verify. > > > > > > Before this fix: > > > > > > /dev/mapper/stripe_dev is a 4-way stripe using a 32k chunksize, so > > > bios are split on 32k boundaries. > > > > > > # fio --name=16M --filename=/dev/mapper/stripe_dev --rw=write --bs=64k --size=16M \ > > > --iodepth=1 --ioengine=libaio --direct=1 --refill_buffers > > > > > > with debugging added: > > > [103898.310264] device-mapper: core: start_io_acct: dm-2 WRITE bio->bi_iter.bi_sector=0 len=128 > > > [103898.318704] device-mapper: core: __split_and_process_bio: recursing for following split bio: > > > [103898.329136] device-mapper: core: start_io_acct: dm-2 WRITE bio->bi_iter.bi_sector=64 len=64 > > > ... > > > > > > 16M written yet 136M (278528 * 512b) accounted: > > > # cat /sys/block/dm-2/stat | awk '{ print $7 }' > > > 278528 > > > > > > After this fix: > > > > > > 16M written and 16M (32768 * 512b) accounted: > > > # cat /sys/block/dm-2/stat | awk '{ print $7 }' > > > 32768 > > > > > > Fixes: 18a25da84354 ("dm: ensure bio submission follows a depth-first tree walk") > > > Cc: stable@vger.kernel.org # 4.16+ > > > Reported-by: Bryan Gurney > > > Reviewed-by: Ming Lei > > > Signed-off-by: Mike Snitzer > > > > > > diff --git a/drivers/md/dm.c b/drivers/md/dm.c > > > index fcb97b0a5743..fbadda68e23b 100644 > > > --- a/drivers/md/dm.c > > > +++ b/drivers/md/dm.c > > > @@ -1584,6 +1584,9 @@ static void init_clone_info(struct clone_info *ci, struct mapped_device *md, > > > ci->sector = bio->bi_iter.bi_sector; > > > } > > > > > > +#define __dm_part_stat_sub(part, field, subnd) \ > > > + (part_stat_get(part, field) -= (subnd)) > > > + > > > /* > > > * Entry point to split a bio into clones and submit them to the targets. > > > */ > > > @@ -1638,6 +1641,19 @@ static blk_qc_t __split_and_process_bio(struct mapped_device *md, > > > struct bio *b = bio_split(bio, bio_sectors(bio) - ci.sector_count, > > > GFP_NOIO, &md->queue->bio_split); > > > ci.io->orig_bio = b; > > > + > > > + /* > > > + * Adjust IO stats for each split, otherwise upon queue > > > + * reentry there will be redundant IO accounting. > > > + * NOTE: this is a stop-gap fix, a proper fix involves > > > + * significant refactoring of DM core's bio splitting > > > + * (by eliminating DM's splitting and just using bio_split) > > > + */ > > > + part_stat_lock(); > > > + __dm_part_stat_sub(&dm_disk(md)->part0, > > > + sectors[op_stat_group(bio_op(bio))], ci.sector_count); > > > + part_stat_unlock(); > > > + > > > bio_chain(b, bio); > > > ret = generic_make_request(bio); > > > break; > > > > > > > Seems to apply fine.. not sure what the problem is on your end: > > > > $ git checkout stable/linux-4.20.y > > Previous HEAD position was 8fe28cb58bcb... Linux 4.20 > > HEAD is now at 9f1a389a0b5b... Linux 4.20.5 > > > > $ git show a1e1cb72d96491277ede8d257ce6b48a381dd336 | patch -p1 --dry > > patching file drivers/md/dm.c > > Hunk #1 succeeded at 1578 (offset -6 lines). > > Hunk #2 succeeded at 1626 (offset -15 lines). > > > > $ git cherry-pick a1e1cb72d96491277ede8d257ce6b48a381dd336 > > [detached HEAD 3d6015ea633a] dm: fix redundant IO accounting for bios that need splitting > > Date: Thu Jan 17 10:48:01 2019 -0500 > > 1 file changed, 16 insertions(+) > > Try building it, it blows up into tiny pieces :) > > I guess I need a different script that says, "the patch applied, but > broke the build", but it is so rare it's almost not worth it... Ah, gotcha. Because of part_stat_get() it implicitly depends on commit 1226b8dd0e913 but that shouldn't go to stable. stable@ would need to factor out __part_stat_sub(), like __part_stat_add(), and part_stat_sub() updated to use __part_stat_sub(). As is, existing part_stat_sub() is broken on all kernels (and with no callers nobody cares). Now that I've woken the dragon (Jens) and told him I papered over block core's broekn part_stat_sub() in DM.. I'll do whatever Jens wants me to do ;) Mike p.s. since this bug has existed for 1.5 years maybe nobody cares that DM's io stats are completely bogus and we can just ignore it? Yeah, that is a cop-out...