linux-kernel - Re: mm_alloc()'ed structure leak

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Date:	Mon, 09 Feb 2009 14:44:09 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	linux-kernel <linux-kernel@...r.kernel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: mm_alloc()'ed structure leak

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?

-- 
Catalin

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