Messages in this thread | | | From | Andy Lutomirski <> | Date | Tue, 16 Oct 2018 14:25:07 -0700 | Subject | Re: [PATCH 1/3] x86/mm/pat: Disable preemption around __flush_tlb_all() |
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On Tue, Oct 16, 2018 at 1:25 PM Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote: > > I've seen the WARN_ON_ONCE(__read_cr3() != build_cr3()) in > switch_mm_irqs_off() every once in a while during a snapshotted system > upgrade. > I also saw the warning early during which was introduced in commit > decab0888e6e ("x86/mm: Remove preempt_disable/enable() from > __native_flush_tlb()"). The callchain is > > get_page_from_freelist() -> post_alloc_hook() -> __kernel_map_pages() > > with CONFIG_DEBUG_PAGEALLOC enabled. > > Turns out, once I disable preemption around __flush_tlb_all() both > warnings do not appear. > > Disable preemption during CR3 reset / __flush_tlb_all(). > > Fixes: decab0888e6e ("x86/mm: Remove preempt_disable/enable() from __native_flush_tlb()") > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> > --- > arch/x86/mm/pageattr.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c > index 51a5a69ecac9f..fe6b21f0a6631 100644 > --- a/arch/x86/mm/pageattr.c > +++ b/arch/x86/mm/pageattr.c > @@ -2088,7 +2088,9 @@ void __kernel_map_pages(struct page *page, int numpages, int enable) > * We should perform an IPI and flush all tlbs, > * but that can deadlock->flush only current cpu: > */ > + preempt_disable(); > __flush_tlb_all(); > + preempt_enable(); >
Depending on your CPU, __flush_tlb_all() is either __native_flush_tlb_global() or __native_flush_tlb(). Only __native_flush_tlb() could have any problem with preemption, but it has a WARN_ON_ONCE(preemptible()); in it. Can you try to figure out why that's not firing for you?
I suspect that a better fix would be to put preempt_disable() into __native_flulsh_tlb(), but I'd still like to understand why the warning isn't working.
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