Re: [COUNTERPATCH] mm: avoid overflowing preempt_count() in mmu_take_all_locks()

Avi Kivity
2010-04-01T16:07:46Z

On 04/01/2010 06:56 PM, Peter Zijlstra wrote:
> On Thu, 2010-04-01 at 18:51 +0300, Avi Kivity wrote:
>
>> On 04/01/2010 06:42 PM, Andrea Arcangeli wrote:
>>
>>> On Thu, Apr 01, 2010 at 01:43:14PM +0200, Peter Zijlstra wrote:
>>>
>>>
>>>> On Thu, 2010-04-01 at 13:27 +0200, Peter Zijlstra wrote:
>>>>
>>>>
>>>>> I've almost got a patch done that converts those two, still need to look
>>>>> where that tasklist_lock muck happens.
>>>>>
>>>>>
>>>> OK, so the below builds and boots, only need to track down that
>>>> tasklist_lock nesting, but I got to run an errand first.
>>>>
>>>>
>>> You should have a look at my old patchset where Christoph already
>>> implemented this (and not for decreasing latency but to allow
>>> scheduling in mmu notifier handlers, only needed by XPMEM):
>>>
>>> http://www.kernel.org/pub/linux/kernel/people/andrea/patches/v2.6/2.6.26-rc7/mmu-notifier-v18/
>>>
>>> The ugliest part of it (that I think you missed below) is the breakage
>>> of the RCU locking in the anon-vma which requires adding refcounting
>>> to it. That was the worst part of the conversion as far as I can tell.
>>>
>>> http://www.kernel.org/pub/linux/kernel/people/andrea/patches/v2.6/2.6.26-rc7/mmu-notifier-v18/anon-vma
>>>
>>>
>> Can we use srcu now instead?
>>
> I would much rather we make call_rcu_preempt() available at all times.
>

I don't understand. I thought the problem was that the locks were taken
inside an rcu critical section; switching to srcu would fix that. But
how is call_rcu_preempt() related? Grepping a bit, what is
call_rcu_preempt()? my tree doesn't have it.

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