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 490A4C7EE21 for ; Thu, 4 May 2023 14:16:47 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A12AA6B0075; Thu, 4 May 2023 10:16:46 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9C2656B0078; Thu, 4 May 2023 10:16:46 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8D85F6B007B; Thu, 4 May 2023 10:16:46 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by kanga.kvack.org (Postfix) with ESMTP id 6BA1C6B0075 for ; Thu, 4 May 2023 10:16:46 -0400 (EDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=8Hnl7RKx0Q6XGEhYYTUEZyfjo56ovfMM3HhYaGLUEew=; b=juJfjc0Yf5CWyCFAP2JWhWBuJ+ RNQBQPJiNd6LgJNn7t9nBYHhSutlYwsNJbdjur9XymvEny7X+wSvNkwxDwT+2VGva/2A6JozpfEG+ tkUKLUTVx30Gr9jI43sgPNdZJucPICfOWUhUVcF6HhgND8ZsnBPYFR1r4Ksn9HKD6CAyVgDySDubL sEnS5tY6vbfV4/Na52UHzcQ8aPBK8tPIrOocU8avbJ62u4J1wO9CBUZ5UO8pnvwIdBs/MbERlT1Ix NNZuyBwO2xEiCwIuMrOzg7ILjjn31107foZ2A3EsQywPR7EPCHm5rHYV9xosLa4YE9RRtuTF/UUe7 PCbgbN1Q==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1puZl9-00AfJJ-68; Thu, 04 May 2023 14:16:39 +0000 Date: Thu, 4 May 2023 15:16:39 +0100 From: Matthew Wilcox To: Christoph Hellwig Cc: Ilya Dryomov , 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 Subject: Re: [PATCH] mm: always respect QUEUE_FLAG_STABLE_WRITES on the block device Message-ID: References: <20230504105624.9789-1-idryomov@gmail.com> <20230504135515.GA17048@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230504135515.GA17048@lst.de> 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 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() has > > the effect of respecting it only when there is a filesystem mounted on > > top of the block device. If a filesystem is not mounted, block devices > > 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 flag > > is captured when the filesystem is mounted and isn't consulted after > > that anywhere outside of swap code, changing it doesn't take immediate > > 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 = folio_inode(folio); > + struct super_block *sb = 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)