kernel warning: tried to kill an mm-less task!

[Li Zefan]

When I ran the same test program I described in a previous patch,
I got the following warning:

WARNING: at mm/oom_kill.c:320 __oom_kill_task+0x6d/0x101()
Modules linked in: 

Pid: 3856, comm: a.out Not tainted 2.6.25-rc8-mm2 #37
 [<ffffffff80243941>] warn_on_slowpath+0x64/0xa2
 [<ffffffff80244e16>] printk+0x5e/0x7b
 [<ffffffff8022b096>] page_count+0x25/0x49
 [<ffffffff8022b2cd>] show_mem+0x125/0x15a
 [<ffffffff8028f00f>] __oom_kill_task+0x6d/0x101
 [<ffffffff8028f319>] oom_kill_process+0x16c/0x22e
 [<ffffffff8028f72c>] select_bad_process+0xb0/0x122
 [<ffffffff8028f8d3>] mem_cgroup_out_of_memory+0x65/0x8a
 [<ffffffff802bee84>] mem_cgroup_charge_common+0xf8/0x215
 [<ffffffff802a14ac>] handle_mm_fault+0x216/0x6c8
 [<ffffffff8029ebca>] follow_page+0x191/0x27d
 [<ffffffff80234155>] need_resched+0x31/0x4f
 [<ffffffff802a1c53>] get_user_pages+0x2f5/0x3eb
 [<ffffffff802a1f64>] make_pages_present+0x9e/0xca
 [<ffffffff802a51fc>] mmap_region+0x38c/0x452
 [<ffffffff802119c4>] arch_get_unmapped_area_topdown+0x1bf/0x2a7
 [<ffffffff802a5971>] do_mmap_pgoff+0x321/0x39b
 [<ffffffff805037ee>] _cond_resched+0x1c/0x5f
 [<ffffffff80211715>] sys_mmap+0xf5/0x138
 [<ffffffff8020c6d2>] tracesys+0xd5/0xda
---[ end trace fe959fb2f0473e7c ]---
tried to kill an mm-less task!

This showed up several times in some seconds, but then didn't appear
any more. And it's reproducable in a x86_64 box, but doesn't happen
in a x86_32 one.

And this happens both with and without the oops fixing.

Regards,
Li Zefan
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