On Tue, Jul 24, 2018 at 04:35:09PM +0200, Sebastian Andrzej Siewior wrote:
> I doubt that there any need to set ->active_mm. It is used by the
> scheduler to keep track of the "currently used mm" so it can reuse one
> for the kernel thread which does not own one and take a reference on it
> so it does not go away while the thread (that borrows it) is active.
> void efi_switch_mm(struct mm_struct *mm)
> {
> - task_lock(current);
> efi_scratch.prev_mm = current->active_mm;
> - current->active_mm = mm;
> switch_mm(efi_scratch.prev_mm, mm, NULL);
> - task_unlock(current);
> }
I think that's broken. Take for instance stuff like
perf_callchain_user32() -> get_segment_base(). That looks at active_mm
to get at the current LDT.
Now, I'm not saying the whole perf vs EFI thing isn't already terminally
wrecked, but the rule is that active_mm really should point at the
current active mm, and the above breaks that.
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