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> Sebastian