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Subject: Re: mm_alloc()'ed structure leak
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@linux-foundation.org>
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Date: Mon, 09 Feb 2009 16:12:43 +0100
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On Mon, 2009-02-09 at 14:44 +0000, Catalin Marinas wrote:
> On Mon, 2009-02-09 at 12:18 +0000, Catalin Marinas wrote:
> > Basically bash forks and executes a command like "host kernel.org" which
> > finishes normally but the corresponding mm_struct isn't freed (I get
> > this consistently every time I run the above command):
> > 
> > unreferenced object 0xcfed4070 (size 368):
> >   comm "bash", pid 1674, jiffies 421592
> >   backtrace:
> >     [<c0082bd4>] kmemleak_alloc+0x140/0x2b0
> >     [<c007ff2c>] kmem_cache_alloc+0xd0/0x100
> >     [<c0036980>] mm_alloc+0x14/0x44
> >     [<c008a99c>] bprm_mm_init+0xc/0x13c
> >     [<c008ab70>] do_execve+0xa4/0x218
> >     [<c002718c>] sys_execve+0x34/0x54
> >     [<c0023e80>] ret_fast_syscall+0x0/0x28
> 
> Dumping the object in question:
> 
> mm_struct.mm_users = 0
> mm_struct.mm_count = 1
> 
> It looks like the mm_count didn't get to 0 hence no structure freeing
> via mmdrop().
> 
> The leak disappears if I revert commit 38d47c1b7075 - "futex: rely on
> get_user_pages() for shared futexes". Peter, any idea?

Looks like the futex key references go wrong somewhere, I'll go look at
it.