linux-ext4 - Re: [PATCH v2] ovl: don't set the superblock's errseq

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Message-ID: <CAOQ4uxhs==_-EM+VyJRRCX_NPmYybPDBW2v7cXz33Qt2RMaPnQ@mail.gmail.com>
Date: Fri, 30 Aug 2024 15:27:35 +0200
From: Amir Goldstein <amir73il@...il.com>
To: Haifeng Xu <haifeng.xu@...pee.com>, "Darrick J. Wong" <djwong@...nel.org>, 
	Jeff Layton <jlayton@...nel.org>, Theodore Tso <tytso@....edu>
Cc: miklos@...redi.hu, linux-unionfs@...r.kernel.org, 
	linux-fsdevel <linux-fsdevel@...r.kernel.org>, Ext4 <linux-ext4@...r.kernel.org>, 
	fstests <fstests@...r.kernel.org>
Subject: Re: [PATCH v2] ovl: don't set the superblock's errseq_t manually

On Tue, Jul 30, 2024 at 6:20 AM Haifeng Xu <haifeng.xu@...pee.com> wrote:
>
> Since commit 5679897eb104 ("vfs: make sync_filesystem return errors from
> ->sync_fs"), the return value from sync_fs callback can be seen in
> sync_filesystem(). Thus the errseq_set opreation can be removed here.
>
> Depends-on: commit 5679897eb104 ("vfs: make sync_filesystem return errors from ->sync_fs")
> Signed-off-by: Haifeng Xu <haifeng.xu@...pee.com>
> Reviewed-by: Amir Goldstein <amir73il@...il.com>
> ---
> Changes since v1:
> - Add Depends-on and Reviewed-by tags.
> ---
>  fs/overlayfs/super.c | 10 ++--------
>  1 file changed, 2 insertions(+), 8 deletions(-)
>
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index 06a231970cb5..fe511192f83c 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -202,15 +202,9 @@ static int ovl_sync_fs(struct super_block *sb, int wait)
>         int ret;
>
>         ret = ovl_sync_status(ofs);
> -       /*
> -        * We have to always set the err, because the return value isn't
> -        * checked in syncfs, and instead indirectly return an error via
> -        * the sb's writeback errseq, which VFS inspects after this call.
> -        */
> -       if (ret < 0) {
> -               errseq_set(&sb->s_wb_err, -EIO);
> +
> +       if (ret < 0)
>                 return -EIO;
> -       }
>
>         if (!ret)
>                 return ret;
> --
> 2.25.1
>

FYI, this change is queued in overlayfs-next.

However, I went to see if overlayfs has test coverage for this and it does not.

The test coverage added by Darrick to the mentioned vfs commit is test xfs/546,
so it does not run on other fs, although it is quite generic.

I fixed this test so it could run on overlayfs (like this):
# This command is complicated a bit because in the case of overlayfs the
# syncfs fd needs to be opened before shutdown and it is different from the
# shutdown fd, so we cannot use the _scratch_shutdown() helper.
# Filter out xfs_io output of active fds.
$XFS_IO_PROG -x -c "open $(_scratch_shutdown_handle)" -c 'shutdown -f
' -c close -c syncfs $SCRATCH_MNT | \
        grep -vF '[00'

and it passes on both xfs and overlayfs (over xfs), but if I try to
make it "generic"
it fails on ext4, which explicitly allows syncfs after shutdown:

        if (unlikely(ext4_forced_shutdown(sb)))
                return 0;

Ted, Darrick,

Do you have any insight as to why this ext4 behavior differs from xfs
or another idea how to exercise the syncfs error in a generic test?

I could fork an overlay/* test from the xfs/* test and require that
underlying fs is xfs, but that would be ugly.

Any ideas?

Thanks,
Amir.