Messages in this thread Patch in this message | | | Date | Tue, 15 Apr 2008 11:47:05 +0800 | From | Li Zefan <> | Subject | Re: kernel warning: tried to kill an mm-less task! |
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CC: Oleg Nesterov <oleg@tv-sign.ru>
Li Zefan wrote: > Balbir Singh wrote: >> Li Zefan wrote: >>> 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. >>> >> Could we get some more details on which task was chosen to be killed? It will be >> nice to see the task flags as well to see if PF_EXITING is set. >> >> oom_kill_task() has a big WARNING in the comment >> >> /* WARNING: mm may not be dereferenced since we did not obtain its >> * value from get_task_mm(p). This is OK since all we need to do is >> * compare mm to q->mm below. >> >> >> I want to see the flags to see if >> >> PF_BORROWED_MM or PF_EXIT* is set. >> >> > > OK, I'll try. > > --
I Added 2 printk()s:
static void __oom_kill_task(struct task_struct *p, int verbose) { + printk(KERN_WARNING "pid = %d, flags = %x\n", p->pid, p->flags); + if (is_global_init(p)) { WARN_ON(1); printk(KERN_WARNING "tried to kill init!\n"); @@ -319,6 +320,7 @@ static void __oom_kill_task(struct task_struct *p, int verbo
if (!p->mm) { WARN_ON(1); + printk(KERN_WARNING "pid = %d, flags = %x\n", p->pid, p->flags); printk(KERN_WARNING "tried to kill an mm-less task!\n"); return; } got this:
pid = 3817, flags = 400140 ------------[ cut here ]------------ WARNING: at mm/oom_kill.c:322 __oom_kill_task+0x74/0xf1() ... ---[ end trace bb92f2fd8fe6c7c5 ]--- pid = 3817, flags = 400144 tried to kill an mm-less task! So PF_EXITING may be set during the call of oom_kill_task(), and I notice the comment in oom_kill_task():
* Furthermore, even if mm contains a non-NULL value, p->mm may * change to NULL at any time since we do not hold task_lock(p). * However, this is of no concern to us.
Is this warning just harmless so that we can just ignore it ?
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