linux-kernel - Re: pidns memory leak

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Date:	Mon, 2 Nov 2009 16:38:18 -0600
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Sukadev Bhattiprolu <sukadev@...ux.vnet.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>,
	Daniel Lezcano <dlezcano@...ibm.com>,
	Pavel Emelianov <xemul@...nvz.org>
Subject: Re: pidns memory leak

Quoting Andrew Morton (akpm@...ux-foundation.org):
> 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?

Well Suka did trace the bug to commit 7766755a2f249e7, and posted a patch
to revert that, acked by Eric on Oct 20.  Suka, were you going to repost
that patch?

-serge
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