Paul Menage wrote:
quoted text
> On Thu, May 15, 2008 at 1:25 AM, Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
>>  >
>>  > But the only *new* cases of taking the mmap_sem that this would
>>  > introduce would be:
>>  >
>>  > - on a failed vm limit charge
>>
>>  Why a failed charge? Aren't we talking of moving all charge/uncharge
>>  under mmap_sem?
>>
> 
> Sorry, I worded that wrongly - I meant "cleaning up a successful
> charge after an expansion fails for other reasons"
> 
> I thought that all the charges and most of the uncharges were already
> under mmap_sem, and it would just be a few of the cleanup paths that
> needed to take it.
> 

OK, that's definitely more meaningful. Thanks for clarifying.

quoted text
>>  > - when a task moves between two cgroups in the memrlimit hierarchy.
>>  >
>>
>>  Yes, this would nest cgroup_mutex and mmap_sem. Not sure if that would
>>  be a bad side-effect.
>>
> 
> I think it's already nested that way - e.g. the cpusets code can call
> various migration functions (which take mmap_sem) while holding
> cgroup_mutex.
> 
>>  Refactor the code to try and use mmap_sem and see what I come up
>>  with. Basically use mmap_sem for all charge/uncharge operations as
>>  well use mmap_sem in read_mode in the move_task() and
>>  mm_owner_changed() callbacks. That should take care of the race
>>  conditions discussed, unless I missed something.
> 
> Sounds good.
> 

Let me get that done and I'll post the next version.

quoted text
> Thanks,
> 
> Paul


-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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