Messages in this thread | | | Date | Fri, 6 Mar 2015 14:46:01 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 1/1] x86/fpu: math_state_restore() should not blindly disable irqs |
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* Oleg Nesterov <oleg@redhat.com> wrote:
> On 03/06, Ingo Molnar wrote: > > > > * Oleg Nesterov <oleg@redhat.com> wrote: > > > > > [...] The patch above looks "obviously safe", but perhaps I am > > > paranoid too much... > > > > IMHO your hack above isn't really acceptable, even for a backport. > > So lets test the patch below (assuming it's the right thing to do) > > and move forward? > > OK, but please note that this patch is not beckportable. If you think > that -stable doesn't need this fix, then I agree. > > If the caller is do_device_not_available(), then we can not enable > irqs before __thread_fpu_begin() + restore_fpu_checking(). > > 1. Preemption in between can destroy ->fpu.state initialized by > fpu_finit(), __switch_to() will save the live (wrong) FPU state > again. > > 2. kernel_fpu_begin() from irq right after __thread_fpu_begin() is > not nice too. It will do __save_init_fpu() and this overwrites > ->fpu.state too. > > Starting from v4.0 it does kernel_fpu_disable(), but the older kernels > do not. > > Ingo, this code is really horrible and fragile. We need to cleanup it > step-by-step, imho.
How about the patch from David Vrabel? That seems to solve the irq-disable problem too, right?
Thanks,
Ingo
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