linux-kernel - Re: [2.6.31 and later] "struct pid" leak.

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Message-ID: <20100401172120.GA3111@us.ibm.com>
Date:	Thu, 1 Apr 2010 12:21:20 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	linux-kernel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Sukadev Bhattiprolu <sukadev@...ibm.com>
Subject: Re: [2.6.31 and later] "struct pid" leak.

Quoting Oleg Nesterov (oleg@...hat.com):
> On 03/31, Andrew Morton wrote:
> >
> > On Tue, 30 Mar 2010 16:31:13 +0100
> > Catalin Marinas <catalin.marinas@....com> wrote:
> >
> > > Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp> wrote:
> > > > I got below report with 2.6.33.1 .
> > > >
> > > > unreferenced object 0xde144600 (size 64):
> > > >   comm "init", pid 1, jiffies 4294678101 (age 291.508s)
> > > >   hex dump (first 32 bytes):
> > > >     02 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> > > >     00 00 00 00 04 76 ae de d1 76 43 c0 d6 08 00 00  .....v...vC.....
> > > >   backtrace:
> > > >     [<c0481704>] create_object+0x121/0x1ef
> > > >     [<c05f546b>] kmemleak_alloc+0x25/0x42
> > > >     [<c047e326>] kmemleak_alloc_recursive+0x1c/0x22
> > > >     [<c047e36e>] kmem_cache_alloc+0x42/0x68
> > > >     [<c0437701>] alloc_pid+0x19/0x288
> > > >     [<c0428acc>] copy_process+0x95a/0xdac
> > > >     [<c04290d8>] do_fork+0x129/0x261
> > > >     [<c0407de5>] sys_clone+0x1f/0x24
> > > >     [<c040292d>] ptregs_clone+0x15/0x28
> > > >     [<ffffffff>] 0xffffffff
> > > > unreferenced object 0xdfa96a40 (size 64):
> > > >   comm "login", pid 2259, jiffies 4294719437 (age 250.179s)
> > > >   hex dump (first 32 bytes):
> > > >     02 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> > > >     00 00 00 00 60 39 ae de d1 76 43 c0 bb 09 00 00  ....`9...vC.....
> > > >   backtrace:
> > > >     [<c0481704>] create_object+0x121/0x1ef
> > > >     [<c05f546b>] kmemleak_alloc+0x25/0x42
> > > >     [<c047e326>] kmemleak_alloc_recursive+0x1c/0x22
> > > >     [<c047e36e>] kmem_cache_alloc+0x42/0x68
> > > >     [<c0437701>] alloc_pid+0x19/0x288
> > > >     [<c0428acc>] copy_process+0x95a/0xdac
> > > >     [<c04290d8>] do_fork+0x129/0x261
> > > >     [<c0407de5>] sys_clone+0x1f/0x24
> > > >     [<c040292d>] ptregs_clone+0x15/0x28
> > > >     [<ffffffff>] 0xffffffff
> > >
> > > I reported similar leaks last year -
> > > http://lkml.org/lkml/2009/7/8/422. There is some analysis in the thread
> > > above of the reference counting but I couldn't figure out where it goes
> > > wrong. It looks to me like there isn't any reference to a struct pid
> > > block but its reference count is 2.
> > >
> > > There is a bugzilla entry as well -
> > > https://bugzilla.kernel.org/show_bug.cgi?id=13868
> > >
> >
> > Let's bug some people by cc'ing them ;)
> 
> Oh. It is hardly possibly to find the unbalanced get_pid() via grep.
> 
> IIRC, I sent the debugging patch which tracks get/put pid, but I can't
> recall if anybody tried this patch. Hmm, and I can't find that patch
> or the previous discussion in my maildir...
> 
> Catalin, Tetsuo, any chance you can remind me if this patch was used?
> 
> Oleg.

[ probably sounding like a moron, but... ]

Looking through vt_ioctl.c, I get the feeling that the ttys will
hang onto vc->vt_pid until either getting a SAK or until someone
new logs in.  I don't see where logging out will cause a reset_vc().
So when the logged in task logs out, does vt_pid keep a ref to the
pid which now no longer exists?

Came to mind bc I notice that every trace you've sent has included
/bin/login or X...

-serge
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