linux-kernel - mm_alloc()'ed structure leak

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Date:	Mon, 09 Feb 2009 12:18:18 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	linux-kernel <linux-kernel@...r.kernel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>
Subject: mm_alloc()'ed structure leak

Hi,

I've noticed on recent kernels (currently 2.6.29-rc3) a memory leak
reported by kmemleak for an mm_struct allocated in mm_alloc(). If that's
a valid leak, it is a pretty serious one.

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

I can't figure out why this structure isn't freed, so any help is
welcomed before I start bisecting. The platform is an ARM one but the
code in question is probably generic.

Thanks.

-- 
Catalin

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