From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 304A5296BCF; Wed, 11 Mar 2026 22:14:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773267250; cv=none; b=ldgedCG4JWtoAT8NEtjJzOeDz/lEwahKUuQvH3ctAcxcznM0IPTEzqOQqnmlng3hLn9Y7TgUEVkdSE3cM7nXuWaKFdCMZ45rKC0dgftWNdqhOWECOpp+hhmhFvjcW7cVayYZAtufP7ySNiw2+zfGWhbNou0ZslqJR7TTEib4NoE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773267250; c=relaxed/simple; bh=O8ufv9orCb9gjhbQTXjts26HeQJe0VHg+7ffSfToflo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=mebG4oYY4n8RRTKEnTmkSas4TOCmF5r0kv8+MKi4Hg3fc6x15c+XKzvE2WOasCTu7TPCOjyC+G76hxT6ftMw/ZDYLRYldgmzo5bkTBYgwyV10oFzfw58kDDkiTalJJXKcBhckFtGkXobE/EFUEI0pCamCFmw39uZ8oOuNtzRnQY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=iQovA7sV; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="iQovA7sV" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A0A46C4CEF7; Wed, 11 Mar 2026 22:14:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773267249; bh=O8ufv9orCb9gjhbQTXjts26HeQJe0VHg+7ffSfToflo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=iQovA7sVKEYkt4XtYecOThXZEBSxyKJkMp0ZKpkUAW2PSJwENulhtJfJZFJjnEvzy Jq1eugqFxCJlaS3C60TkvvT59m3meVQ5YLhBWuo6gGEsZWlqYzL78KOMcEqeFZ+wgf d1DDB3LKvL0j+pWSzjlOwtOCYnyeePMxo0/D9zKARRJKtn1t2YjFxmFjWLZt16ejFG tqEkuDCng6sIUATbgUFh3JGFHnMeiRZ8ea+uh3Xx+/KJF3RD+zfKTGh3TMDTFCgMKv gN55jiKnrnOuoSTfc5maOhOGbhlGRWJ49LCf5rDIRzQaPr45QA1tCK1AEcmRsUQsEl m8PVfk5khZz+g== Date: Wed, 11 Mar 2026 15:14:08 -0700 From: "Darrick J. Wong" To: Brian Foster Cc: linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org Subject: Re: [PATCH v4 2/8] xfs: flush dirty pagecache over hole in zoned mode zero range Message-ID: <20260311221408.GE1770774@frogsfrogsfrogs> References: <20260311162502.192375-1-bfoster@redhat.com> <20260311162502.192375-3-bfoster@redhat.com> Precedence: bulk X-Mailing-List: linux-xfs@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: <20260311162502.192375-3-bfoster@redhat.com> On Wed, Mar 11, 2026 at 12:24:56PM -0400, Brian Foster wrote: > For zoned filesystems a window exists between the first write to a > sparse range (i.e. data fork hole) and writeback completion where we > might spuriously observe holes in both the COW and data forks. This > occurs because a buffered write populates the COW fork with > delalloc, writeback submission removes the COW fork delalloc blocks > and unlocks the inode, and then writeback completion remaps the > physically allocated blocks into the data fork. If a zero range > operation does a lookup during this window where both forks show a > hole, it incorrectly reports a hole mapping for a range that > contains data. > > This currently works because iomap checks for dirty pagecache over > holes and unwritten mappings. If found, it flushes and retries the > lookup. We plan to remove the hole flush logic from iomap, however, > so lift the flush into xfs_zoned_buffered_write_iomap_begin() to > preserve behavior and document the purpose for it. Zoned XFS > filesystems don't support unwritten extents, so if zoned mode can > come up with a way to close this transient hole window in the > future, this flush can likely be removed. > > Signed-off-by: Brian Foster > Reviewed-by: Christoph Hellwig > --- > fs/xfs/xfs_iomap.c | 19 +++++++++++++++++++ > 1 file changed, 19 insertions(+) > > diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c > index 8c3469d2c73e..d3b8c018c883 100644 > --- a/fs/xfs/xfs_iomap.c > +++ b/fs/xfs/xfs_iomap.c > @@ -1590,6 +1590,7 @@ xfs_zoned_buffered_write_iomap_begin( > { > struct iomap_iter *iter = > container_of(iomap, struct iomap_iter, iomap); > + struct address_space *mapping = inode->i_mapping; > struct xfs_zone_alloc_ctx *ac = iter->private; > struct xfs_inode *ip = XFS_I(inode); > struct xfs_mount *mp = ip->i_mount; > @@ -1614,6 +1615,7 @@ xfs_zoned_buffered_write_iomap_begin( > if (error) > return error; > > +restart: > error = xfs_ilock_for_iomap(ip, flags, &lockmode); > if (error) > return error; > @@ -1686,8 +1688,25 @@ xfs_zoned_buffered_write_iomap_begin( > * When zeroing, don't allocate blocks for holes as they are already > * zeroes, but we need to ensure that no extents exist in both the data > * and COW fork to ensure this really is a hole. > + * > + * A window exists where we might observe a hole in both forks with > + * valid data in cache. Writeback removes the COW fork blocks on > + * submission but doesn't remap into the data fork until completion. If > + * the data fork was previously a hole, we'll fail to zero. Until we > + * find a way to avoid this transient state, check for dirty pagecache > + * and flush to wait on blocks to land in the data fork. > */ > if ((flags & IOMAP_ZERO) && srcmap->type == IOMAP_HOLE) { > + if (filemap_range_needs_writeback(mapping, offset, > + offset + count - 1)) { > + xfs_iunlock(ip, lockmode); > + error = filemap_write_and_wait_range(mapping, offset, > + offset + count - 1); > + if (error) > + return error; > + goto restart; > + } Seems fine to me. Reviewed-by: "Darrick J. Wong" --D > + > xfs_hole_to_iomap(ip, iomap, offset_fsb, end_fsb); > goto out_unlock; > } > -- > 2.52.0 > >