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=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 44C1EC4361B for ; Wed, 16 Dec 2020 15:16:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E4AE8233CF for ; Wed, 16 Dec 2020 15:15:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726356AbgLPPPo (ORCPT ); Wed, 16 Dec 2020 10:15:44 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:47961 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726371AbgLPPPo (ORCPT ); Wed, 16 Dec 2020 10:15:44 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1608131657; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=OfDj4DJaoB++2KIjkmOLDB1ZfXvWoRXRp8J5NFncySc=; b=QMv0KY5VHXii8GUlZzBBitSDGV8EGuWiW60o1noUXgZoRZbJqIuoqPeH4GTdCmx0SNA7f+ 6Nz/jfJk/UI7vkUXNsJAjDa2oV+g7zPb0+G5J4Iw3AnstrQTOZs1c+9+PRvh4Im2DPS8Pb yq+YBxm2zUi7go8XjErBPDIOgzbIoVE= 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-575-r1I8TnV4MYmAaZJGsd23gQ-1; Wed, 16 Dec 2020 10:14:12 -0500 X-MC-Unique: r1I8TnV4MYmAaZJGsd23gQ-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 6E0CD800D53; Wed, 16 Dec 2020 15:14:10 +0000 (UTC) Received: from horse.redhat.com (ovpn-112-114.rdu2.redhat.com [10.10.112.114]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4C4AB19CAC; Wed, 16 Dec 2020 15:14:10 +0000 (UTC) Received: by horse.redhat.com (Postfix, from userid 10451) id C3283220BCF; Wed, 16 Dec 2020 10:14:09 -0500 (EST) Date: Wed, 16 Dec 2020 10:14:09 -0500 From: Vivek Goyal To: Jeff Layton Cc: Linux fsdevel mailing list , linux-unionfs@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk, miklos@szeredi.hu, amir73il@gmail.com, willy@infradead.org, jack@suse.cz, sargun@sargun.me Subject: Re: [PATCH] vfs, syncfs: Do not ignore return code from ->sync_fs() Message-ID: <20201216151409.GA3177@redhat.com> References: <20201216143802.GA10550@redhat.com> <132c8c1e1ab82f5a640ff1ede6bb844885d46e68.camel@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <132c8c1e1ab82f5a640ff1ede6bb844885d46e68.camel@kernel.org> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: linux-unionfs@vger.kernel.org On Wed, Dec 16, 2020 at 09:57:49AM -0500, Jeff Layton wrote: > On Wed, 2020-12-16 at 09:38 -0500, Vivek Goyal wrote: > > I see that current implementation of __sync_filesystem() ignores the > > return code from ->sync_fs(). I am not sure why that's the case. > > > > Ignoring ->sync_fs() return code is problematic for overlayfs where > > it can return error if sync_filesystem() on upper super block failed. > > That error will simply be lost and sycnfs(overlay_fd), will get > > success (despite the fact it failed). > > > > I am assuming that we want to continue to call __sync_blockdev() > > despite the fact that there have been errors reported from > > ->sync_fs(). So I wrote this simple patch which captures the > > error from ->sync_fs() but continues to call __sync_blockdev() > > and returns error from sync_fs() if there is one. > > > > There might be some very good reasons to not capture ->sync_fs() > > return code, I don't know. Hence thought of proposing this patch. > > Atleast I will get to know the reason. I still need to figure > > a way out how to propagate overlay sync_fs() errors to user > > space. > > > > Signed-off-by: Vivek Goyal > > --- > >  fs/sync.c | 8 ++++++-- > >  1 file changed, 6 insertions(+), 2 deletions(-) > > > > Index: redhat-linux/fs/sync.c > > =================================================================== > > --- redhat-linux.orig/fs/sync.c 2020-12-16 09:15:49.831565653 -0500 > > +++ redhat-linux/fs/sync.c 2020-12-16 09:23:42.499853207 -0500 > > @@ -30,14 +30,18 @@ > >   */ > >  static int __sync_filesystem(struct super_block *sb, int wait) > >  { > > + int ret, ret2; > > + > >   if (wait) > >   sync_inodes_sb(sb); > >   else > >   writeback_inodes_sb(sb, WB_REASON_SYNC); > >   > > > >   if (sb->s_op->sync_fs) > > - sb->s_op->sync_fs(sb, wait); > > - return __sync_blockdev(sb->s_bdev, wait); > > + ret = sb->s_op->sync_fs(sb, wait); > > + ret2 = __sync_blockdev(sb->s_bdev, wait); > > + > > + return ret ? ret : ret2; > >  } > >   > > > >  /* > > > > I posted a patchset that took a similar approach a couple of years ago, > and we decided not to go with it [1]. > > While it's not ideal to ignore the error here, I think this is likely to > break stuff. So one side affect I see is that syncfs() might start returning errors in some cases which were not reported at all. I am wondering will that count as breakage. > What may be better is to just make sync_fs void return, so > people don't think that returned errors there mean anything. May be. But then question remains that how do we return error to user space in syncfs(fd) for overlayfs. I will not be surprised if other filesystems want to return errors as well. Shall I create new helpers and call these in case of syncfs(). But that too will start returning new errors on syncfs(). So it does not solve that problem (if it is a problem). Or we can define a new super block op say ->sync_fs2() and call that first and in that case capture return code. That way it will not impact existing cases and overlayfs can possibly make use of ->sync_fs2() and return error. IOW, impact will be limited to only file systems which chose to implement ->sync_fs2(). Thanks Vivek > > [1]: https://lore.kernel.org/linux-fsdevel/20180518123415.28181-1-jlayton@kernel.org/ > -- > Jeff Layton >