On 2019-08-14 14:39:10 [+0100], Mark Rutland wrote: > I think this was missed in commit. > > 8d3289f2fa1e0 ("x86/fpu: Don't use current->mm to check for a kthread") > > Yup, though if it's a bug it's been a bug since commit: > > 0cecca9d03c964ab ("x86/fpu: Eager switch PKRU state") > > ... which I guess the fixes tag would have to mention. > > > > > A kthread with use_mm() would load here non-existing FPU state. > > > > Acked-by: Sebastian Andrzej Siewior <bige...@linutronix.de> > > Given the above, should I add the fixes tag (for 0cecca9d03c964ab)?
Buh. Either that or hch's commit (8d3289f2fa1e0 ("x86/fpu: Don't use current->mm to check for a kthread"). That will trigger a stable backport (for 5.2) asking what to do about is_kthread() so please leave a hint to use the PF_ flag like hch did. Now that I think about it, even if we end up in kthread with use_mm() then its FPU state is non-existent which means get_xsave_addr() returns NULL. This is okay / expected but it triggers the WARN_ONCE(). > Thanks, > Mark. Sebastian