Re: How to avoid spurious lockdep warnings?

[Jeremy Fitzhardinge <jeremy@goop.org>]

Arjan van de Ven wrote:
> On Thu, 20 Mar 2008 16:02:11 -0700
> Jeremy Fitzhardinge <jeremy@goop.org> wrote:
>
>   
>> In a Xen system, when a new pagetable is about to be put in use it is 
>> "pinned", meaning that each page in the pagetable is registered with
>> the hypervisor.  This is done in arch/x86/xen/mmu.c:pin_page().
>>
>> In order to make this efficient, the hypercalls for pinning are
>> batched, so that multiple pages are submitted at once in a single
>> multicall. While a page is batched pending the hypercall, its
>> corresponding pte_lock is held.
>>
>> This means that the code can end up holding multiple pte locks at
>> once, though it is guaranteed to never try to hold the same lock at
>> once. However, because these locks are in the same lock class, I get
>> a spurious warning from lockdep.  Is there some way I can get rid of
>> this warning?
>>     
>
>
> what's the ordering guarantee between these locks ?
>   

Pagetable virtual address order.  move_ptes can also lock two ptes 
within one pagetable, without regard to order, but they're protected by 
mmap_sem, which is also held during pinning.

    J