linux-kernel - Re: [????] Re: divide error in x86 and cputime

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Message-ID: <aVrN7zNyo3v-y_m3@redhat.com>
Date: Sun, 4 Jan 2026 21:30:39 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: David Laight <david.laight.linux@...il.com>
Cc: Xia Fukun <xiafukun@...wei.com>, Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	"Li,Rongqing" <lirongqing@...du.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"vschneid@...hat.com" <vschneid@...hat.com>,
	"mgorman@...e.de" <mgorman@...e.de>,
	"bsegall@...gle.com" <bsegall@...gle.com>,
	"rostedt@...dmis.org" <rostedt@...dmis.org>,
	"dietmar.eggemann@....com" <dietmar.eggemann@....com>,
	"vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
	"juri.lelli@...hat.com" <juri.lelli@...hat.com>,
	"Zhangqiao (2012 lab)" <zhangqiao22@...wei.com>
Subject: Re: [????] Re: divide error in x86 and cputime

On 01/04, David Laight wrote:
>
> On Sun, 4 Jan 2026 15:23:19 +0100
> Oleg Nesterov <oleg@...hat.com> wrote:
>
> > Peter, Ingo,
> >
> > can you take
> >
> > 	[PATCH v3 0/2] x86/math64: handle #DE in mul_u64_u64_div_u64()
> > 	https://lore.kernel.org/all/20250815164009.GA11676@redhat.com/
> >
> > ? at least 1/2 which fixes the problem with #DE ...
>

...

> But this code needs a completely different fix.

Of course, this is clear. The fix above doesn't even try to address the
problems in cputime_adjust() paths.

But. To me the fix above makes sense regardless. mul_u64_u64_div_u64()
should nevet trigger #DE, and I thought that we already discussed this
before.

Do you agree?

Oleg.