Balbir Singh wrote:
> * KAMEZAWA Hiroyuki <[EMAIL PROTECTED]> [2008-12-11 10:05:01]:
>
>> On Wed, 10 Dec 2008 16:52:57 -0800
>> Paul Menage <[EMAIL PROTECTED]> wrote:
>>
>>> On Wed, Dec 10, 2008 at 4:49 PM, KAMEZAWA Hiroyuki
>>> <[EMAIL PROTECTED]> wrote:
>>>> an operation like rmdir() in somewhere.
>>>> hierarchy_lock for A (acquired)
>>>> hierarchy_lock for B (waiting)
>>>>
>>>> in subsys A.
>>>> mmap_sem (acquired)
>>>> hierarchy_lock for A (waiting)
>>>> in subsys B.
>>>> hierarchy_lock for B (aquired)
>>>> mmap_sem (waiting)
>>>>
>>> That's a valid deadlock - you'd need to require the mmap_sem nests
>>> either inside all hierarchy_mutexes or else outside all of them.
>>>
>> This was a found dead lock between memcg and cpuset.
>>
>> another one was
>>
>> an operation like rmdir() in somewhere.
>> hierarchy_lock for memcg (acquired)
>> hierarchy_lock for B (waiting)
>>
>> in subsys B.
>> hierarchy_lock for B (aquired)
>
> But then the hierarchy_locks acquired will be different right?
>
Yes, I'm worrying this too. The lock order by cgroup_lock_hierarchy() is:
lock A -> lock B -> lock C
But a call chain may end up with:
... -> lock B -> ... lock A -> ...
So though this hierarchy lock proprosal can solve specific deadlock between
cpuset and memcg by making cpuset holding cgroup_lock and memcg holding
hierarchy_lock,
but we'll probably encounter other deadlocks describled above.
>> have to do some memory reclaim -> hierarchy_lock for memcg
>> (waiting)
>>
>> I have no objections to hierarchy_lock itself but calling context to memcg
>> is very
>> complicated and simple replace of these locks will be just a small help.
>
> Could you please explain the race better?
>
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