Re: [PATCH 1/4] generic: check userspace handling of extreme timestamps

From: Amir Goldstein <amir73il@gmail.com>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: Eryu Guan <guaneryu@gmail.com>,
	linux-xfs <linux-xfs@vger.kernel.org>,
	fstests <fstests@vger.kernel.org>,
	Deepa Dinamani <deepa.kernel@gmail.com>
Subject: Re: [PATCH 1/4] generic: check userspace handling of extreme timestamps
Date: Thu, 29 Oct 2020 23:40:00 +0200	[thread overview]
Message-ID: <CAOQ4uxjZ7tpkJAXVHWvj5M0G4QM4vSeQ+GXszSij7wVbePJdXw@mail.gmail.com> (raw)
In-Reply-To: <20201029205543.GC1061252@magnolia>

On Thu, Oct 29, 2020 at 11:02 PM Darrick J. Wong
<darrick.wong@oracle.com> wrote:
>
> On Thu, Oct 29, 2020 at 12:34:57PM +0200, Amir Goldstein wrote:
> > On Wed, Oct 28, 2020 at 10:25 PM Darrick J. Wong
> > <darrick.wong@oracle.com> wrote:
> > >
> > > From: Darrick J. Wong <darrick.wong@oracle.com>
> > >
> > > These two tests ensure we can store and retrieve timestamps on the
> > > extremes of the date ranges supported by userspace, and the common
> > > places where overflows can happen.
> > >
> > > They differ from generic/402 in that they don't constrain the dates
> > > tested to the range that the filesystem claims to support; we attempt
> > > various things that /userspace/ can parse, and then check that the vfs
> > > clamps and persists the values correctly.
> >
> > So this test will fail when run on stable kernels before the vfs
> > clamping changes
> > and there is no require_* to mitigate that failure.
>
> Yes, that is the intended outcome.  Those old kernels silently truncate
> the high bits from those timestamps when inodes are flushed to disk, and
> the only user-visible evidence of this comes much later when the system
> reboots and suddenly the timestamps are wrong.  Clamping also seems a
> little strange, but at least it's immediately obvious.
>
> It is very surprising that you could set a timestamp of 2 Apr 2500 on
> ext2, ls your shiny futuristic timestamp, reboot, and have it become
> 5 Nov 1955.  Only Marty McFly would be amused.
>

OK. So we can call it a bug in old kernels that is not going to be fixed
in stable updates. The minimum we can do for stable kernel testers is
provide a decent way to exclude the tests for clamping.

I guess 'check -x bigtime' is decent enough.
I might have named the group 'timelimit' but I can live with 'bigtime'.

So with fix for the rest of my minor nits, you may add:

Reviewed-by: Amir Goldstein <amir73il@gmail.com>

Thanks,
Amir.