[Intel-wired-lan] [PATCH] i40e: fix i40e_ptp_adjtime when given a negative delta

[Keller, Jacob E]

> -----Original Message-----
> From: Arnd Bergmann [mailto:arnd at arndb.de]
> Sent: Monday, March 25, 2019 9:45 AM
> To: Keller, Jacob E <jacob.e.keller at intel.com>
> Cc: Intel Wired LAN <intel-wired-lan at lists.osuosl.org>; Kirsher, Jeffrey T
> <jeffrey.t.kirsher at intel.com>
> Subject: Re: [PATCH] i40e: fix i40e_ptp_adjtime when given a negative delta
> 
> On Mon, Feb 25, 2019 at 8:46 PM Arnd Bergmann <arnd at arndb.de> wrote:
> >
> > On Mon, Feb 25, 2019 at 8:20 PM Jacob Keller <jacob.e.keller at intel.com> wrote:
> > >
> > > Commit 0ac30ce43323 ("i40e: fix up 32 bit timespec references",
> > > 2017-07-26) claims to be cleaning up references to 32-bit timespecs.
> > >
> > > The actual contents of the commit make no sense, as it converts a call
> > > to timespec64_add into timespec64_add_ns. This would seem ok, if (a) the
> > > change was documented in the commit message, and (b) timespec64_add_ns
> > > supported negative numbers.
> > >
> > > timespec64_add_ns doesn't work with signed deltas, because the
> > > implementation is based around iter_div_u64_rem. This change resulted in
> > > a regression where i40e_ptp_adjtime would interpret small negative
> > > adjustments as large positive additions, resulting in incorrect
> > > behavior.
> > >
> > > This commit doesn't appear to fix anything, is not well explained, and
> > > introduces a bug, so lets just revert it.
> >
> > Ah, this is not the bug I was referring to but actually worse.
> > I was only worried about hogging the CPU while doing billions
> > of additions in a loop, and had not realized it also changes
> > the result.
> >
> > > Reverts: 0ac30ce43323 ("i40e: fix up 32 bit timespec references", 2017-07-26)
> > > Signed-off-by: Jacob Keller <jacob.e.keller at intel.com>
> >
> > Reviewed-by: Arnd Bergmann <arnd at arndb.de>
> 
> Any update on this? Your patch doesn't seem to have made it in as
> a bugfix, or into linux-next yet.
> 
>        Arnd

It's still marked as under review on patchworks. It was marked as tested by Andrew Bowers, so I am not sure what else holdup is.

Jeff?

I think this patch could/should go through net because it's a bug fix.

Thanks,
Jake