On 2019-08-14 11:41:30 [+0100], Mark Rutland wrote:
> Per commit:
>   0cecca9d03c964ab ("x86/fpu: Eager switch PKRU state")
> ... switch_fpu_state() is trying to distinguish user threads from
> kthreads, such that kthreads consistently use init_pkru_value. It does
> do by looking at current->mm.
> In general, a non-NULL current->mm doesn't imply that current is a
> kthread, as kthreads can install an mm via use_mm(), and so it's
> preferable to use is_kthread() to determine whether a thread is a
> kthread.

I think this was missed in commit.
        8d3289f2fa1e0 ("x86/fpu: Don't use current->mm to check for a kthread")

A kthread with use_mm() would load here non-existing FPU state.

Acked-by: Sebastian Andrzej Siewior <bige...@linutronix.de>


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