Re: [PATCH 1/1] x86/fpu: math_state_restore() should not blindly disable irqs

Oleg Nesterov
2015-03-06T14:20:06Z

On 03/06, Oleg Nesterov wrote:
>
> On 03/06, Ingo Molnar wrote:
> >
> > How about the patch from David Vrabel? That seems to solve the
> > irq-disable problem too, right?
>
> I wasn't cc'ed, I guess you mean
>
> [PATCHv4] x86, fpu: remove the logic of non-eager fpu mem allocation at the first usage
> http://marc.info/?l=linux-kernel&m=142564237705311&w=2
>
> Not sure I understand it correctly after the first quick look, but
>
> 1. It conflicts with the recent changes in tip/x86/fpu
>
> 2. fpu_ini() initializes current->thread.fpu.state. This looks unneeded,
> the kernel threads no longer have FPU context and do not abuse CPU.
>
> 3. I can be easily wrong, but it looks buggy... Note that
> arch_dup_task_struct() doesn't allocate child->fpu.state if
> !tsk_used_math(parent).
>
> Add David...
>
> No, I do not think this patch is a good idea. Perhaps I am wrong, but I
> think we need other changes. And they should start from init_fpu().

But the change in eager_fpu_init_bp() looks good (on top of tip/x86/fpu),
at least I was going to do the same ;)

In any case, I do not think this patch can target -stable.

Oleg.