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    SubjectRe: [PATCH 1/1] x86/fpu: math_state_restore() should not blindly disable irqs
    On 03/06, Linus Torvalds wrote:
    >
    > On Thu, Mar 5, 2015 at 11:58 PM, Ingo Molnar <mingo@kernel.org> wrote:
    > >
    > > math_state_restore() was historically called with irqs disabled,
    > > because that's how the hardware generates the trap, and also because
    > > back in the days it was possible for it to be an asynchronous
    > > interrupt and interrupt handlers run with irqs off.
    > >
    > > These days it's always an instruction trap, and furthermore it does
    > > inevitably complex things such as memory allocation and signal
    > > processing, which is not done with irqs disabled.
    > >
    > > So keep irqs enabled.
    >
    > I agree with the "keep irqs enabled".

    Me too, but not for stable. This patch is wrong without other changes.

    > IOW, I think the starting point should be something like the attached
    > (which doesn't do the WARN_ON_ONCE() - it should be added for
    > debugging).

    Yes, agreed.

    And. Even if we forget about stable, we need some minor changes before
    this one. At least we need to add preempt_disable() into kernel_fpu_disable().


    So I still think that the horrible hack I sent makes sense for -stable.
    Just we need to cleanup (kill) it "immediately".

    Oleg.



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