From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B5E8D330B08 for ; Wed, 5 Nov 2025 15:30:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762356605; cv=none; b=jtCGd9wrC8E8gBhkhR5BuFzH6L/32OvidOKlkZYY6aSLInQ72V091NPLnP1y08w/gh6Jl+Pz16tS2oPDEVuo9e8tw7oyO6PirF8bmuwgRGvcahVoyEbbIan9dhKCZBWP/qHCE7/Zod49Y/GE5ghBVtItj+EOa/24t6I2Sj09EK0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762356605; c=relaxed/simple; bh=7cUNMKsjvauMVU1hKnLcdZdiUsNtjytp9rxPdMfNcps=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ryStuJgD60HP1xm3TsRnA1AFnkgYl61PfSBuzKXCDJztJoUEm7619KgiivVmg/X5yUJWO3NoXwqVpZtQnX0SRoQTIqmYP+T4YKZ8trXE6CCAIJSY30LngLrehjdULkh7OceFaeJrnsDSlGRR65CHNycKmHAQzWlBZrNdwl1XnA0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=MTbnzvUp; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="MTbnzvUp" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1762356602; 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: in-reply-to:in-reply-to:references:references; bh=saQftPy6Ee7T13PU0SmdxbZdndk5kz3SiIUEfliij6Q=; b=MTbnzvUpHeu8Ado1jVqPHB4thC8IzMu+g5YvhKJ/NOU1JpFaBBD/KNMiltCWZWv+Wva2lV ebANRS7baYB1y7yEqGVRJ9IffdN5NjaVY6RR5p105OY7FlKsYsthtMxMr8xmrkO8lff7Xi WFqwm+NvI1iT5L0f8Vac1XUgPj3T8gI= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-258-BoJleAWaPmWuhAYWXCGLCw-1; Wed, 05 Nov 2025 10:29:59 -0500 X-MC-Unique: BoJleAWaPmWuhAYWXCGLCw-1 X-Mimecast-MFC-AGG-ID: BoJleAWaPmWuhAYWXCGLCw_1762356598 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 5F6AF180122B; Wed, 5 Nov 2025 15:29:58 +0000 (UTC) Received: from bfoster (unknown [10.22.88.135]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 98C78300018D; Wed, 5 Nov 2025 15:29:57 +0000 (UTC) Date: Wed, 5 Nov 2025 10:34:26 -0500 From: Brian Foster To: "Darrick J. Wong" Cc: linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org Subject: Re: [PATCH 3/6] xfs: flush eof folio before insert range size update Message-ID: References: <20251016190303.53881-1-bfoster@redhat.com> <20251016190303.53881-4-bfoster@redhat.com> <20251105001445.GW196370@frogsfrogsfrogs> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251105001445.GW196370@frogsfrogsfrogs> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 On Tue, Nov 04, 2025 at 04:14:45PM -0800, Darrick J. Wong wrote: > On Thu, Oct 16, 2025 at 03:03:00PM -0400, Brian Foster wrote: > > The flush in xfs_buffered_write_iomap_begin() for zero range over a > > data fork hole fronted by COW fork prealloc is primarily designed to > > provide correct zeroing behavior in particular pagecache conditions. > > As it turns out, this also partially masks some odd behavior in > > insert range (via zero range via setattr). > > > > Insert range bumps i_size the length of the new range, flushes, > > unmaps pagecache and cancels COW prealloc, and then right shifts > > extents from the end of the file back to the target offset of the > > insert. Since the i_size update occurs before the pagecache flush, > > this creates a transient situation where writeback around EOF can > > behave differently. > > Why not flush the file from @offset to EOF, flush the COW > preallocations, extend i_size, and only then start shifting extents? > That would seem a lot more straightforward to me. > I agree. I noted in the cover letter that I started with this approach of reordering the existing sequence of operations, but the factoring looked ugly enough that I stopped and wanted to solicit input. The details of that fell out of my brain since I posted this, unfortunately. I suspect it may have been related to layering or something wrt the prepare_shift factoring, but I'll take another look in that direction for v2 and once I've got some feedback on the rest of the series.. Thanks. Brian > --D > > > This appears to be corner case situation, but if happens to be > > fronted by COW fork speculative preallocation and a large, dirty > > folio that contains at least one full COW block beyond EOF, the > > writeback after i_size is bumped may remap that COW fork block into > > the data fork within EOF. The block is zeroed and then shifted back > > out to post-eof, but this is unexpected in that it leads to a > > written post-eof data fork block. This can cause a zero range > > warning on a subsequent size extension, because we should never find > > blocks that require physical zeroing beyond i_size. > > > > To avoid this quirk, flush the EOF folio before the i_size update > > during insert range. The entire range will be flushed, unmapped and > > invalidated anyways, so this should be relatively unnoticeable. > > > > Signed-off-by: Brian Foster > > --- > > fs/xfs/xfs_file.c | 17 +++++++++++++++++ > > 1 file changed, 17 insertions(+) > > > > diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c > > index 5b9864c8582e..cc3a9674ad40 100644 > > --- a/fs/xfs/xfs_file.c > > +++ b/fs/xfs/xfs_file.c > > @@ -1226,6 +1226,23 @@ xfs_falloc_insert_range( > > if (offset >= isize) > > return -EINVAL; > > > > + /* > > + * Let writeback clean up EOF folio state before we bump i_size. The > > + * insert flushes before it starts shifting and under certain > > + * circumstances we can write back blocks that should technically be > > + * considered post-eof (and thus should not be submitted for writeback). > > + * > > + * For example, a large, dirty folio that spans EOF and is backed by > > + * post-eof COW fork preallocation can cause block remap into the data > > + * fork. This shifts back out beyond EOF, but creates an expectedly > > + * written post-eof block. The insert is going to flush, unmap and > > + * cancel prealloc across this whole range, so flush EOF now before we > > + * bump i_size to provide consistent behavior. > > + */ > > + error = filemap_write_and_wait_range(inode->i_mapping, isize, isize); > > + if (error) > > + return error; > > + > > error = xfs_falloc_setsize(file, isize + len); > > if (error) > > return error; > > -- > > 2.51.0 > > > > >