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From:   Amir Goldstein <amir73il@gmail.com>
Date:   Mon, 25 Nov 2019 19:35:12 +0200
Message-ID: <CAOQ4uxh3OMmVotx-v9Lnvwcs7zxeBs9Ag9Q0uUK6f2v2Yqto5Q@mail.gmail.com>
Subject: Re: [PATCH] utimes: Clamp the timestamps in notify_change()
To:     "J . Bruce Fields" <bfields@fieldses.org>
Cc:     Arnd Bergmann <arnd@arndb.de>,
        Deepa Dinamani <deepa.kernel@gmail.com>,
        Jeff Layton <jlayton@kernel.org>,
        Miklos Szeredi <miklos@szeredi.hu>,
        Al Viro <viro@zeniv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        overlayfs <linux-unionfs@vger.kernel.org>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        y2038@lists.linaro.org
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On Mon, Nov 25, 2019 at 6:46 PM J . Bruce Fields <bfields@fieldses.org> wrote:
>
> On Sun, Nov 24, 2019 at 09:31:45PM +0200, Amir Goldstein wrote:
> > Push clamping timestamps down the call stack into notify_change(), so
> > in-kernel callers like nfsd and overlayfs will get similar timestamp
> > set behavior as utimes.
>
> So, nfsd has always bypassed timestamp_truncate() and we've never
> noticed till now?  What are the symptoms?  (Do timestamps go backwards
> after cache eviction on filesystems with large time granularity?)

Clamping seems to be new behavior since v5.4-rc1.
Before that clamping was done implicitly when hitting the disk IIUC,
so it was observed mostly after cache eviction.

>
> Looks like generic/402 has never run in my tests:
>
>         generic/402     [not run] no kernel support for y2038 sysfs switch
>

The test in its current form is quite recent as well or at the _require
has changed recently.
See acb2ba78 - overlay: support timestamp range check

You'd probably need something similar for nfs (?)

Thanks,
Amir.