Re: [????] Re: divide error in x86 and cputime

[David Laight]

On Sun, 4 Jan 2026 21:30:39 +0100
Oleg Nesterov <oleg@xxxxxxxxxx> wrote:

> On 01/04, David Laight wrote:
> >
> > On Sun, 4 Jan 2026 15:23:19 +0100
> > Oleg Nesterov <oleg@xxxxxxxxxx> 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@xxxxxxxxxx/
> > >
> > > ? 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?

Yes, I think both the generic and x86 versions should just return ~0ull
for both overflow and divide by zero.

	David

> 
> Oleg.
>