Messages in this thread | | | Date | Tue, 15 Feb 2011 21:26:35 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [PATCH] fix pgd_lock deadlock |
| |
On Tue, 15 Feb 2011, Thomas Gleixner wrote:
> 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?
Another thing. You check for in_interrupt(), but what makes sure that the code which takes pgd_lock is never taken with interrupts disabled except during early boot ?
Thanks,
tglx
| |