linux-kernel - Re: [PATCH AUTOSEL 5.14 46/99] ovl: copy up sync/noatime fileattr flags

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Message-ID: <CAOQ4uxi8Ae8Pk1bUDNmQgCvEn_SoXXeW4HsNV5k2+ceejevrLQ@mail.gmail.com>
Date:   Fri, 10 Sep 2021 08:35:41 +0300
From:   Amir Goldstein <amir73il@...il.com>
To:     Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>,
        Miklos Szeredi <mszeredi@...hat.com>,
        overlayfs <linux-unionfs@...r.kernel.org>
Subject: Re: [PATCH AUTOSEL 5.14 46/99] ovl: copy up sync/noatime fileattr flags

On Fri, Sep 10, 2021 at 3:17 AM Sasha Levin <sashal@...nel.org> wrote:
>
> From: Amir Goldstein <amir73il@...il.com>
>
> [ Upstream commit 72db82115d2bdfbfba8b15a92d91872cfe1b40c6 ]
>
> When a lower file has sync/noatime fileattr flags, the behavior of
> overlayfs post copy up is inconsistent.
>
> Immediately after copy up, ovl inode still has the S_SYNC/S_NOATIME
> inode flags copied from lower inode, so vfs code still treats the ovl
> inode as sync/noatime.  After ovl inode evict or mount cycle,
> the ovl inode does not have these inode flags anymore.
>
> To fix this inconsistency, try to copy the fileattr flags on copy up
> if the upper fs supports the fileattr_set() method.
>
> This gives consistent behavior post copy up regardless of inode eviction
> from cache.
>
> We cannot copy up the immutable/append-only inode flags in a similar
> manner, because immutable/append-only inodes cannot be linked and because
> overlayfs will not be able to set overlay.* xattr on the upper inodes.
>
> Those flags will be addressed by a followup patch.
>
> Signed-off-by: Amir Goldstein <amir73il@...il.com>
> Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---

Sasha,

I do not recommend applying this patch to stable.
The value/risk ratio is not worth it IMO.

I don't know of anyone who ever complained about not copying
the NOATIME/SYNC fileattrs specifically.

This patch is more of a complimentary patch to the IMMUTABLE/
APPEND fileattr patch, which is not appropriate for stable either.

OTOH, ovl-update-5.15 has this patch that was not included in the
AUTOSEL batch, even though it has a Fixes tag, CC stable and
very strong hints in the subject:
52d5a0c6bd8a ("ovl: fix BUG_ON() in may_delete() when called from
ovl_cleanup()")

I suppose AUTOSEL leaves these sorts of patches to Greg's scripts?

Thanks,
Amir.