Re: [RFC PATCH 08/11] x86,fpu: restore user FPU state lazily after __kernel_fpu_end

Oleg Nesterov
2015-01-14T19:09:22Z

On 01/14, Oleg Nesterov wrote:
>
> On 01/11, riel@redhat.com wrote:
> >
> > --- a/arch/x86/kernel/i387.c
> > +++ b/arch/x86/kernel/i387.c
> > @@ -89,13 +89,11 @@ void __kernel_fpu_end(void)
> > if (use_eager_fpu()) {
> > /*
> > * For eager fpu, most the time, tsk_used_math() is true.
> > - * Restore the user math as we are done with the kernel usage.
> > - * At few instances during thread exit, signal handling etc,
> > - * tsk_used_math() is false. Those few places will take proper
> > - * actions, so we don't need to restore the math here.
> > + * Make sure the user math state is restored on return to
> > + * userspace.
> > */
> > if (likely(tsk_used_math(current)))
> > - math_state_restore();
> > + set_thread_flag(TIF_LOAD_FPU);
>
> Hmm. And this looks obviously wrong if interrupted_user_mode().

OOPS, sorry, I misread this change.

Oleg.