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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 55260C77B78 for ; Thu, 4 May 2023 15:07:24 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A74446B007B; Thu, 4 May 2023 11:07:23 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9FD9A6B007D; Thu, 4 May 2023 11:07:23 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8C6016B007E; Thu, 4 May 2023 11:07:23 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from mail-ed1-f48.google.com (mail-ed1-f48.google.com [209.85.208.48]) by kanga.kvack.org (Postfix) with ESMTP id 3BEA86B007B for ; Thu, 4 May 2023 11:07:23 -0400 (EDT) Received: by mail-ed1-f48.google.com with SMTP id 4fb4d7f45d1cf-50bd2d7ba74so18151713a12.1 for ; Thu, 04 May 2023 08:07:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20221208; t=1683212842; x=1685804842; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:from:to:cc:subject:date :message-id:reply-to; bh=9WFS1x47blclBXskP77nCF58D51Rpg9+wJAmzlYQmRk=; b=iOENyJgHIcqMP2+ca+2v80DT2ibR3iO9OVec9sAfKp7iLNAEq9mujvSiuMFX0BeHxf FXeeGNJEllsKwvy5a7JoPvL5PkZDu7W3NmC/C+73rZwfW4xKcrl2OUlXbzgVBx9jb5s5 3zmGR16y/wilEY8jd7r7+vccxMYIjQq9Gr8pKGIXxn+nE11U6nj5XCsdwj97PPQkmqYt F8RnwS5MsdoCAwdzSCN2vL5FoakB8av51upu1FZinjJDEwDrPYO0+Wzm/oJWGSjScrVQ QptWn+fjuB0LzpTlL4bdxjJ9Vm9todUZ0BCPONAUOiMTsuJBDn82A34/N137dRuh+b6F Mawg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1683212842; x=1685804842; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=9WFS1x47blclBXskP77nCF58D51Rpg9+wJAmzlYQmRk=; b=C8vxX+D6SK8F2lDBxx4GZgtCMzd/cF5LXrCpAAuYqtmA2JzUFheiL9FQjncXvLYegW rPWjhnxasho6w0YW+zfBcEX7HHcmpzuAGtWJvYcg9S9UgTGfgtZWtrUd61T5N6dXBQi2 qQwFV/gHO9pHBl/n3H9fqKvLAakgH/8YCF2tiPYk26qZlUsjR2RYay+/mdA/E21CcD3/ 4DctLRLKsPkiGwHDjuT/VyQRyhi6cvttMRU6PpysmNI6Tp81TPc8hN630Bi4yOtJ0goK NFwaGvq4iMJIhYxHfT9qKWerZSL3IDgkziH79w5g1lZgHWlyxNpd5T2/pwX/s7OfEm+j xozg== X-Gm-Message-State: AC+VfDwbW/03laTMdUxborROeGnzIYu5GBYUM0VvkT+jWfBPkqX9UTUb NYVB6dDhRunajycBJUbmGbA+dNcY3R4uNGJYTY4= X-Google-Smtp-Source: ACHHUZ4EZmZqjOJWc+m9y3XiZVF1YH6IrfUtVWGSTRu5Mvda+qI8kMR4AtvmrTycSugn84PacQcC4fD2dgIHHkhmutU= X-Received: by 2002:a17:906:9746:b0:960:ddba:e5bf with SMTP id o6-20020a170906974600b00960ddbae5bfmr5322943ejy.0.1683212842404; Thu, 04 May 2023 08:07:22 -0700 (PDT) MIME-Version: 1.0 References: <20230504105624.9789-1-idryomov@gmail.com> <20230504135515.GA17048@lst.de> In-Reply-To: From: Ilya Dryomov Date: Thu, 4 May 2023 17:07:10 +0200 Message-ID: Subject: Re: [PATCH] mm: always respect QUEUE_FLAG_STABLE_WRITES on the block device To: Matthew Wilcox Cc: Christoph Hellwig , Jan Kara , Johannes Thumshirn , Jens Axboe , linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, May 4, 2023 at 4:16=E2=80=AFPM Matthew Wilcox = wrote: > > On Thu, May 04, 2023 at 03:55:15PM +0200, Christoph Hellwig wrote: > > On Thu, May 04, 2023 at 12:56:24PM +0200, Ilya Dryomov wrote: > > > Commit 1cb039f3dc16 ("bdi: replace BDI_CAP_STABLE_WRITES with a queue > > > and a sb flag") introduced a regression for the raw block device use > > > case. Capturing QUEUE_FLAG_STABLE_WRITES flag in set_bdev_super() ha= s > > > the effect of respecting it only when there is a filesystem mounted o= n > > > top of the block device. If a filesystem is not mounted, block devic= es > > > that do integrity checking return sporadic checksum errors. > > > > With "If a file system is not mounted" you want to say "when accessing > > a block device directly" here, right? The two are not exclusive.. > > > > > Additionally, this commit made the corresponding sysfs knob writeable > > > for debugging purposes. However, because QUEUE_FLAG_STABLE_WRITES fl= ag > > > is captured when the filesystem is mounted and isn't consulted after > > > that anywhere outside of swap code, changing it doesn't take immediat= e > > > effect even though dumping the knob shows the new value. With no way > > > to dump SB_I_STABLE_WRITES flag, this is needlessly confusing. > > > > But very much intentional. s_bdev often is not the only device > > in a file system, and we should never reference if from core > > helpers. > > > > So I think we should go with something like this: > > > > diff --git a/mm/page-writeback.c b/mm/page-writeback.c > > index db794399900734..aa36cc2a4530c1 100644 > > --- a/mm/page-writeback.c > > +++ b/mm/page-writeback.c > > @@ -3129,7 +3129,11 @@ EXPORT_SYMBOL_GPL(folio_wait_writeback_killable)= ; > > */ > > void folio_wait_stable(struct folio *folio) > > { > > - if (folio_inode(folio)->i_sb->s_iflags & SB_I_STABLE_WRITES) > > + struct inode *inode =3D folio_inode(folio); > > + struct super_block *sb =3D inode->i_sb; > > + > > + if ((sb->s_iflags & SB_I_STABLE_WRITES) || > > + (sb_is_blkdev_sb(sb) && bdev_stable_writes(I_BDEV(inode)))) > > folio_wait_writeback(folio); > > } > > EXPORT_SYMBOL_GPL(folio_wait_stable); > > I hate both of these patches ;-) What we should do is add > AS_STABLE_WRITES, have the appropriate places call > mapping_set_stable_writes() and then folio_wait_stable() becomes > > if (mapping_test_stable_writes(folio->mapping)) > folio_wait_writeback(folio); > > and we remove all the dereferences (mapping->host->i_sb->s_iflags, plus > whatever else is going on there) Hi Matthew, We would still need something resembling Christoph's suggestion for 5.10 and 5.15 (at least). Since this fixes a regression, would you support merging the "ugly" version to facilitate backports or would you rather see the AS/mapping-based refactor first? Thanks, Ilya