linux-kernel - Re: [PATCH] overlayfs: set ctime when setting mtime and atime

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Message-ID: <b107db96b12f4ab5b2edfbaa42bc0032205d24cc.camel@kernel.org>
Date:   Thu, 14 Sep 2023 06:27:15 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     Amir Goldstein <amir73il@...il.com>
Cc:     Miklos Szeredi <miklos@...redi.hu>,
        Nathan Chancellor <nathan@...nel.org>,
        Christian Brauner <brauner@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-unionfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] overlayfs: set ctime when setting mtime and atime

On Wed, 2023-09-13 at 20:36 +0300, Amir Goldstein wrote:
> On Wed, Sep 13, 2023 at 4:33 PM Jeff Layton <jlayton@...nel.org> wrote:
> > 
> > Nathan reported that he was seeing the new warning in
> > setattr_copy_mgtime pop when starting podman containers. Overlayfs is
> > trying to set the atime and mtime via notify_change without also
> > setting the ctime.
> > 
> > POSIX states that when the atime and mtime are updated via utimes() that
> > we must also update the ctime to the current time. The situation with
> > overlayfs copy-up is analogous, so add ATTR_CTIME to the bitmask.
> > notify_change will fill in the value.
> > 
> 
> IDGI, if ctime always needs to be set along with ATIME / MTIME, why not
> let notify_change() set the bit instead of assert and fix all the callers?
> But maybe I am missing something.
> 

Traditionally notify_change has always been given an explicit mask of
attrs to change by the caller. I'm a little hesitant to start putting
POSIX policy in there.

Still, that may be the better thing to do over the long haul. I think
that there are some other bugs in the notify_change callers as well: for
instance, cachefiles_adjust_size truncates files, but doesn't update the
timestamps. I'm pretty sure that's wrong.

I think if we want to change how setattr ctime updates work, we'll
probably need to do it in the context of a larger notify_change
overhaul.

> Anyway, I have no objection to the ovl patch.
> It's fine by me if Christian applies it to the vfs.ctime branch with my ACK.
> 

Many thanks!

> Thanks,
> Amir.
> 
> > Reported-by: Nathan Chancellor <nathan@...nel.org>
> > Signed-off-by: Jeff Layton <jlayton@...nel.org>
> > ---
> > The new WARN_ON_ONCE in setattr_copy_mgtime caught a bug! Fix up
> > overlayfs to ensure that the ctime on the upper inode is also updated
> > when copying up the atime and mtime.
> > ---
> >  fs/overlayfs/copy_up.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
> > index d1761ec5866a..ada3fcc9c6d5 100644
> > --- a/fs/overlayfs/copy_up.c
> > +++ b/fs/overlayfs/copy_up.c
> > @@ -337,7 +337,7 @@ static int ovl_set_timestamps(struct ovl_fs *ofs, struct dentry *upperdentry,
> >  {
> >         struct iattr attr = {
> >                 .ia_valid =
> > -                    ATTR_ATIME | ATTR_MTIME | ATTR_ATIME_SET | ATTR_MTIME_SET,
> > +                    ATTR_ATIME | ATTR_MTIME | ATTR_ATIME_SET | ATTR_MTIME_SET | ATTR_CTIME,
> >                 .ia_atime = stat->atime,
> >                 .ia_mtime = stat->mtime,
> >         };
> > 
> > ---
> > base-commit: 9cb8e7c86ac793862e7bea7904b3426942bbd7ef
> > change-id: 20230913-ctime-299173760dd9
> > 
> > Best regards,
> > --
> > Jeff Layton <jlayton@...nel.org>
> > 

-- 
Jeff Layton <jlayton@...nel.org>