From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <48042539.8050009@cn.fujitsu.com> Date: Tue, 15 Apr 2008 11:47:05 +0800 From: Li Zefan MIME-Version: 1.0 Subject: Re: kernel warning: tried to kill an mm-less task! References: <4803030D.3070906@cn.fujitsu.com> <48030F69.7040801@linux.vnet.ibm.com> <48031090.5050002@cn.fujitsu.com> In-Reply-To: <48031090.5050002@cn.fujitsu.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: balbir@linux.vnet.ibm.com Cc: "linux-mm@kvack.org" , LKML , Andrew Morton , KAMEZAWA Hiroyuki , Pavel Emelianov , Oleg Nesterov Oleg Nesterov List-ID: 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 >>> [] warn_on_slowpath+0x64/0xa2 >>> [] printk+0x5e/0x7b >>> [] page_count+0x25/0x49 >>> [] show_mem+0x125/0x15a >>> [] __oom_kill_task+0x6d/0x101 >>> [] oom_kill_process+0x16c/0x22e >>> [] select_bad_process+0xb0/0x122 >>> [] mem_cgroup_out_of_memory+0x65/0x8a >>> [] mem_cgroup_charge_common+0xf8/0x215 >>> [] handle_mm_fault+0x216/0x6c8 >>> [] follow_page+0x191/0x27d >>> [] need_resched+0x31/0x4f >>> [] get_user_pages+0x2f5/0x3eb >>> [] make_pages_present+0x9e/0xca >>> [] mmap_region+0x38c/0x452 >>> [] arch_get_unmapped_area_topdown+0x1bf/0x2a7 >>> [] do_mmap_pgoff+0x321/0x39b >>> [] _cond_resched+0x1c/0x5f >>> [] sys_mmap+0xf5/0x138 >>> [] 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 ? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org