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=-7.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 A9CC2C433DF for ; Tue, 23 Jun 2020 17:16:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8386820780 for ; Tue, 23 Jun 2020 17:16:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="MsZFxbRX" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732548AbgFWRQB (ORCPT ); Tue, 23 Jun 2020 13:16:01 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:25185 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728916AbgFWRQA (ORCPT ); Tue, 23 Jun 2020 13:16:00 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1592932558; 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=L7YTMHwGFM/8UvyaH+thFi3hyeOfENr0NBI+YuGKZ+A=; b=MsZFxbRXquIfiQufYAIRvRCd12tde9JzpKcWk0Utvrsl5UhhK4c9pEMkrDY0shmWEa9+vh 6FI1k+0+MDoH7IE/vXTQEEZ4x9kfry2SCjp67V7zHYfsJLcx4pzLXA7piuQDpI6OXX5LKj uXydnxnaZh2OhxhRP0cSYRSdfB6bXNw= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-367-xRLCioPfNZa9dY69Fgn0qg-1; Tue, 23 Jun 2020 13:15:57 -0400 X-MC-Unique: xRLCioPfNZa9dY69Fgn0qg-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 15CB7107ACCD; Tue, 23 Jun 2020 17:15:54 +0000 (UTC) Received: from bfoster (dhcp-41-2.bos.redhat.com [10.18.41.2]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 80DDE5DD63; Tue, 23 Jun 2020 17:15:53 +0000 (UTC) Date: Tue, 23 Jun 2020 13:15:51 -0400 From: Brian Foster To: "Darrick J. Wong" Cc: xfs , Dave Chinner Subject: Re: [PATCH v2] xfs: don't eat an EIO/ENOSPC writeback error when scrubbing data fork Message-ID: <20200623171551.GB56510@bfoster> References: <20200623035010.GF7606@magnolia> <20200623121031.GB55038@bfoster> <20200623152350.GE7625@magnolia> <20200623164934.GA56510@bfoster> <20200623170054.GF7625@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200623170054.GF7625@magnolia> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Sender: linux-xfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Tue, Jun 23, 2020 at 10:00:54AM -0700, Darrick J. Wong wrote: > On Tue, Jun 23, 2020 at 12:49:34PM -0400, Brian Foster wrote: > > On Tue, Jun 23, 2020 at 08:23:50AM -0700, Darrick J. Wong wrote: > > > On Tue, Jun 23, 2020 at 08:10:31AM -0400, Brian Foster wrote: > > > > On Mon, Jun 22, 2020 at 08:50:10PM -0700, Darrick J. Wong wrote: > > > > > From: Darrick J. Wong > > > > > > > > > > The data fork scrubber calls filemap_write_and_wait to flush dirty pages > > > > > and delalloc reservations out to disk prior to checking the data fork's > > > > > extent mappings. Unfortunately, this means that scrub can consume the > > > > > EIO/ENOSPC errors that would otherwise have stayed around in the address > > > > > space until (we hope) the writer application calls fsync to persist data > > > > > and collect errors. The end result is that programs that wrote to a > > > > > file might never see the error code and proceed as if nothing were > > > > > wrong. > > > > > > > > > > xfs_scrub is not in a position to notify file writers about the > > > > > writeback failure, and it's only here to check metadata, not file > > > > > contents. Therefore, if writeback fails, we should stuff the error code > > > > > back into the address space so that an fsync by the writer application > > > > > can pick that up. > > > > > > > > > > Fixes: 99d9d8d05da2 ("xfs: scrub inode block mappings") > > > > > Signed-off-by: Darrick J. Wong > > > > > --- > > > > > v2: explain why it's ok to keep going even if writeback fails > > > > > --- > > > > > fs/xfs/scrub/bmap.c | 19 ++++++++++++++++++- > > > > > 1 file changed, 18 insertions(+), 1 deletion(-) > > > > > > > > > > diff --git a/fs/xfs/scrub/bmap.c b/fs/xfs/scrub/bmap.c > > > > > index 7badd6dfe544..0d7062b7068b 100644 > > > > > --- a/fs/xfs/scrub/bmap.c > > > > > +++ b/fs/xfs/scrub/bmap.c > > > > > @@ -47,7 +47,24 @@ xchk_setup_inode_bmap( > > > > > sc->sm->sm_type == XFS_SCRUB_TYPE_BMBTD) { > > > > > inode_dio_wait(VFS_I(sc->ip)); > > > > > error = filemap_write_and_wait(VFS_I(sc->ip)->i_mapping); > > > > > - if (error) > > > > > + if (error == -ENOSPC || error == -EIO) { > > > > > + /* > > > > > + * If writeback hits EIO or ENOSPC, reflect it back > > > > > + * into the address space mapping so that a writer > > > > > + * program calling fsync to look for errors will still > > > > > + * capture the error. > > > > > + * > > > > > + * However, we continue into the extent mapping checks > > > > > + * because write failures do not necessarily imply > > > > > + * anything about the correctness of the file metadata. > > > > > + * The metadata and the file data could be on > > > > > + * completely separate devices; a media failure might > > > > > + * only affect a subset of the disk, etc. We properly > > > > > + * account for delalloc extents, so leaving them in > > > > > + * memory is fine. > > > > > + */ > > > > > + mapping_set_error(VFS_I(sc->ip)->i_mapping, error); > > > > > > > > I think the more appropriate thing to do is open code the data write and > > > > wait and use the variants of the latter that don't consume address space > > > > errors in the first place (i.e. filemap_fdatawait_keep_errors()). Then > > > > we wouldn't need the special error handling branch or perhaps the first > > > > part of the comment. Hm? > > > > > > Yes, it's certainly possible. I don't want to go opencoding more vfs > > > methods (like some e4 filesystems do) so I'll propose that as a second > > > patch for 5.9. > > > > > > > What's the point of fixing it twice when the generic code already > > exports the appropriate helpers? filemap_fdatawrite() and > > filemap_fdatawait_keep_errors() are used fairly commonly afaict. That > > seems much more straightforward to me than misusing a convenience helper > > and trying to undo the undesirable effects after the fact. > > Blergh. Apparently my eyes suck at telling fdatawait from fdatawrite > and I got all twisted around. Now I realize that I think you were > asking why I didn't simply call: > > filemap_flush() > filemap_fdatawait_keep_errors() > > one after the other? And yes, that's way better than throwing error > codes back into the mapping. I'll do that, thanks. > Yeah basically, though I was looking more at filemap_fdatawrite() simply because it's analogous to the write component of filemap_write_and_wait(). It looks like the only difference with filemap_flush() is it uses WB_SYNC_NONE instead of WB_SYNC_ALL. Perhaps either one is fine from here.. > > > On second thought, I wonder if I should just drop the flush entirely? > > > It's not a huge burden to skip past the delalloc reservations. > > > > > > Hmmm. Any preferences? > > > > > > > The context for the above is not clear to me. If the purpose is to check > > on-disk metadata, shouldn't we flush the in-core content first? It would seem > > a little strange to me for one file check to behave differently from > > another if the only difference between the two is that some or more of a > > file had been written back, but maybe I'm missing details.. > > Originally it was because the bmap scrubber didn't handle delalloc > extents, but that was changed long ago. Nowadays it only exists as a > precautionary "try to push everything to disk" tactic. > Ok. When you mention "skip past the delalloc reservations" above that implies to me we'd skip some processing/validation bits. If that's not the case then perhaps it doesn't matter as much... Brian > --D > > > Brian > > > > > --D > > > > > > > Brian > > > > > > > > > + } else if (error) > > > > > goto out; > > > > > } > > > > > > > > > > > > > > > > > > > >