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SubjectRe: [PATCH 2/3] x86, fpu: unlazy_fpu: don't do __thread_fpu_end() if use_eager_fpu()
On 01/29/2015 04:08 PM, Oleg Nesterov wrote:
> unlazy_fpu()->__thread_fpu_end() doesn't look right if use_eager_fpu().
> Unconditional __thread_fpu_end() is only correct if we know that this
> thread can't return to user-mode and use FPU.
>
> Fortunately it has only 2 callers. fpu_copy() checks use_eager_fpu(),
> and init_fpu(current) can be only called by the coredumping thread via
> regset->get(). But it is exported to modules, and imo this should be
> fixed anyway.
>
> And if we check use_eager_fpu() we can use __save_fpu() like fpu_copy()
> and save_init_fpu() do.
>
> - It seems that even !use_eager_fpu() case doesn't need the unconditional
> __thread_fpu_end(), we only need it if __save_init_fpu() returns 0.
>
> - It is still not clear to me if __save_init_fpu() can safely nest with
> another save + restore from __kernel_fpu_begin(). If not, we can use
> kernel_fpu_disable() to fix the race.
>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

Reviewed-by: Rik van Riel <riel@redhat.com>



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