Messages in this thread | | | From | Linus Torvalds <> | Date | Tue, 17 Oct 2023 14:53:33 -0700 | Subject | Re: [PATCH v2 -tip] x86/percpu: Use C for arch_raw_cpu_ptr() |
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On Tue, 17 Oct 2023 at 14:06, Uros Bizjak <ubizjak@gmail.com> wrote: > > But adding the attached patch on top of both patches boots OK.
Funky.
Mind adding a
WARN_ON_ONCE(!active_mm);
to there to give a nice backtrace for the odd NULL case.
That code *is* related to 'current', in how we do
tsk = current; ... local_irq_disable(); active_mm = tsk->active_mm; tsk->active_mm = mm; tsk->mm = mm; ... activate_mm(active_mm, mm); ... mmdrop_lazy_tlb(active_mm);
but I don't see how 'active_mm' could *poossibly* be validly NULL here, and why caching 'current' would matter and change it.
Strange.
Hmm. We do set
tsk->active_mm = NULL;
in copy_mm(), and then we have that odd kernel thread case:
/* * Are we cloning a kernel thread? * * We need to steal a active VM for that.. */ oldmm = current->mm; if (!oldmm) return 0;
but none of this should even matter, because by the time we actually *schedule* that thread, we'll set active_mm to the right thing.
Can anybody see what's up?
Linus
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