linux-kernel - Re: pidns memory leak

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Date:	Tue, 13 Oct 2009 23:15:33 -0700
From:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To:	Daniel Lezcano <dlezcano@...ibm.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	andrea@...share.com, "Eric W. Biederman" <ebiederm@...ssion.com>,
	Linux Containers <containers@...ts.osdl.org>,
	Pavel Emelianov <xemul@...nvz.org>
Subject: Re: pidns memory leak

Daniel Lezcano [dlezcano@...ibm.com] wrote:
> Sukadev Bhattiprolu wrote:
>> Ccing  Andrea's new email id:
>>
>> Daniel Lezcano [dlezcano@...ibm.com] wrote:
>>   
>>> Following your explanation I was able to reproduce a simple program   
>>> added in attachment. But there is something I do not understand is 
>>> why  the leak does not appear if I do the 'lstat' (cf. test program) 
>>> in the  pid 2 context.
>>>     
>>
>> Hmm, are you sure there is no leak with this test program ? If I put back
>> the commit (7766755a2f249e7), I do see a leak in all three data structures
>> (pid_2, proc_inode, pid_namespace).
>>   
>
> Let me clarify :)
>
> The program leaks with the commit 7766755a2f249e7 and does not leak  
> without this commit.
> This is the expected behaviour and this simple program spots the problem.
>
> I tried to modify the program and I moved the lstat to the process 2 in  
> the child namespace. Conforming your analysis, I was expecting to see a  
> leak too, but this one didn't occur. I was wondering why, maybe there is  
> something I didn't understood in the analysis.

Hmm, There are two separate dentries associated with the processes.
One in each mount of /proc. The proc dentries in the child container
are freed when the child container unmounts its /proc so you don't see
the leak when the lstat() is inside the container.

When the lstat() is in the root container, it is accessing proc-dentries
from the _root container_ - They are supposed to  be flushed when the task
exits (but the above commit prevents that flush). They should be freed
when the /proc in root container is unmounted - and leak until then ?

Sukadev
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