linux-kernel - Re: pidns memory leak

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Message-Id: <20091102133326.e3dc51fb.akpm@linux-foundation.org>
Date:	Mon, 2 Nov 2009 13:33:26 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Cc:	Daniel Lezcano <dlezcano@...ibm.com>,
	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

On Tue, 13 Oct 2009 23:15:33 -0700
Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com> wrote:

> 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 ?
> 

This bug hasn't been fixed yet, has it?
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