Re: [PATCH 2/3] x86, xsave: remove thread_has_fpu() bug check in__sanitize_i387_state()

[Oleg Nesterov]

Hi Suresh,

I can't really comment this series, my understanding of this code
is too limited.

But could you explain this patch? I am just curious.

On 05/08, Suresh Siddha wrote:
>
> BUG_ON() in __sanitize_i387_state() is checking that the fpu state
> is not live any more. But for preempt kernels, task can be scheduled
> out and in at any place and the preload_fpu logic during context switch
> can make the fpu registers live again.

And? Do you see any particular scenario when this BUG_ON() is wrong?

Afaics, __sanitize_i387_state() should not be called if the task can
be scheduled in with ->fpu_counter != 0.

> Similarly during core dump, thread dumping the core can schedule out
> and in for page-allocations etc in non-preempt case.

Again, can't understand. The core-dumping thread does init_fpu()
before it calls sanitize_i387_state().

Oleg.

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