Re: mm_alloc()'ed structure leak

Catalin Marinas
2009-02-09T14:45:09Z

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