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

Jeff Kirsher jeffrey.t.kirsher at intel.com
Tue Mar 26 22:05:13 UTC 2019


On Mon, 2019-03-25 at 10:23 -0700, Keller, Jacob E wrote:
> > -----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.

I apologize, I got bogged down with ice driver patches.  I will push
the fix to Dave's net tree now.
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