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

From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Amir Goldstein <amir73il@gmail.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 14:59:02 -0700	[thread overview]
Message-ID: <20201029215902.GL1061252@magnolia> (raw)
In-Reply-To: <CAOQ4uxjZ7tpkJAXVHWvj5M0G4QM4vSeQ+GXszSij7wVbePJdXw@mail.gmail.com>

On Thu, Oct 29, 2020 at 11:40:00PM +0200, Amir Goldstein wrote:
> 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:

Ok, I've fixed them all.  I also added warnings to 721 and 722 that the
test is expected to fail on pre-5.4 kernels.  Thanks for reviewing!

--D

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