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

[Arnd Bergmann]

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