On Wed, Jul 26, 2017 at 12:33 PM Jeff Kirsher
<jeffrey.t.kirs...@intel.com> wrote:
>
> From: Jesse Brandeburg <jesse.brandeb...@intel.com>
>
> As it turns out there was only a small set of errors
> on 32 bit, and we just needed to be using the right calls
> for dealing with timespec64 variables.
I just stumbled over code added by this older patch, and can't make sense
of the commit description here. Was this an attempt to fix a bug, or
just a cleanup?
>
> - then = ns_to_timespec64(delta);
> mutex_lock(&pf->tmreg_lock);
>
> i40e_ptp_read(pf, &now);
> - now = timespec64_add(now, then);
> + timespec64_add_ns(&now, delta);
> i40e_ptp_write(pf, (const struct timespec64 *)&now);
The problem I noticed here is that 'delta' is a user provided 64-bit
number from clock_adjtime(), and timespec64_add_ns() performs uses
a repeated addition instead of a div/mod pair. When the number
is large, we may end up adding a single second 8 billion times,
which may take a while even on a fast CPU.
Should the commit 0ac30ce43323 ("i40e: fix up 32 bit timespec
references") just be reverted?
Arnd
