Messages in this thread | | | Date | Tue, 15 Feb 2011 21:05:20 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [PATCH] fix pgd_lock deadlock |
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On Tue, 15 Feb 2011, Andrea Arcangeli wrote: > On Tue, Feb 15, 2011 at 08:26:51PM +0100, Thomas Gleixner wrote: > > With NR_CPUs < 4, or with THP enabled, rmap.c will do > spin_lock(&mm->page_table_lock) (or pte_offset_map_lock where the lock > is still mm->page_table_lock and not the PT lock). Then it will send > IPIs to flush the tlb of the other CPUs. > > But the other CPU is running the vmalloc_sync_all, and it is trying to > take the page_table_lock with irq disabled. It will never take the > lock because the CPU waiting the IPI delivery holds it. And it will > never run the IPI because it has irqs disabled.
Ok, that makes sense :)
> Now the big question is if anything is taking the pgd_lock from > irqs. Normal testing could never reveal it as even if it happens it > has a slim chance to happen while the pgd_lock is already hold by > normal kernel context. But the VM_BUG_ON(in_interrupt()) should > hopefully have revealed it already if it ever happened, I hope. > > Clearly we could try to fix it in other ways, but still if there's no > reason to do the _irqsave this sounds a good idea to apply my fix > anyway.
Did you try with DEBUG_PAGEALLOC, which is calling into cpa quite a lot?
Thanks,
tglx
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