> Od: Johannes Weiner <hannes@xxxxxxxxxxx>
> Komu: "Ma, Xindong" <xindong.ma@xxxxxxxxx>
> Dátum: 28.11.2013 07:54
> Predmet: Re: [PATCH] Fix race between oom kill and task exit
>
> CC: "akpm@xxxxxxxxxxxxxxxxxxxx" <akpm@xxxxxxxxxxxxxxxxxxxx>, "mhocko@xxxxxxx" <mhocko@xxxxxxx>, "rientjes@xxxxxxxxxx" <rientjes@xxxxxxxxxx>, "rusty@xxxxxxxxxxxxxxx" <rusty@xxxxxxxxxxxxxxx>, "linux-mm@xxxxxxxxx" <linux-mm@xxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, "'Peter Zijlstra'" <peterz@xxxxxxxxxxxxx>, "'gregkh@xxxxxxxxxxxxxxxxxxx'" <gregkh@xxxxxxxxxxxxxxxxxxx>, "Tu, Xiaobing" <xiaobing.tu@xxxxxxxxx>, "William Dauchy" <wdauchy@xxxxxxxxx>
>Cc William and azur who might have encountered this problem.
>
>On Thu, Nov 28, 2013 at 05:09:16AM +0000, Ma, Xindong wrote:
>> From: Leon Ma <xindong.ma@xxxxxxxxx>
>> Date: Thu, 28 Nov 2013 12:46:09 +0800
>> Subject: [PATCH] Fix race between oom kill and task exit
>>
>> There is a race between oom kill and task exit. Scenario is:
>> TASK A TASK B
>> TASK B is selected to oom kill
>> in oom_kill_process()
>> check PF_EXITING of TASK B
>> task call do_exit()
>> task set PF_EXITING flag
>> write_lock_irq(&tasklist_lock);
>> remove TASK B from thread group in __unhash_process()
>> write_unlock_irq(&tasklist_lock);
>> read_lock(&tasklist_lock);
>> traverse threads of TASK B
>> read_unlock(&tasklist_lock);
>>
>> After that, the following traversal of threads in TASK B will not end because TASK B is not in the thread group:
>> do {
>> ....
>> } while_each_thread(p, t);
>>
>> Signed-off-by: Leon Ma <xindong.ma@xxxxxxxxx>
>> Signed-off-by: xiaobing tu <xiaobing.tu@xxxxxxxxx>
>> ---
>> mm/oom_kill.c | 20 ++++++++++----------
>> 1 files changed, 10 insertions(+), 10 deletions(-)
>>
>> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
>> index 1e4a600..32ec88d 100644
>> --- a/mm/oom_kill.c
>> +++ b/mm/oom_kill.c
>> @@ -412,16 +412,6 @@ void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
>> static DEFINE_RATELIMIT_STATE(oom_rs, DEFAULT_RATELIMIT_INTERVAL,
>> DEFAULT_RATELIMIT_BURST);
>>
>> - /*
>> - * If the task is already exiting, don't alarm the sysadmin or kill
>> - * its children or threads, just set TIF_MEMDIE so it can die quickly
>> - */
>> - if (p->flags & PF_EXITING) {
>> - set_tsk_thread_flag(p, TIF_MEMDIE);
>> - put_task_struct(p);
>> - return;
>> - }
>> -
>> if (__ratelimit(&oom_rs))
>> dump_header(p, gfp_mask, order, memcg, nodemask);
>>
>> @@ -437,6 +427,16 @@ void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
>> * still freeing memory.
>> */
>> read_lock(&tasklist_lock);
>> + /*
>> + * If the task is already exiting, don't alarm the sysadmin or kill
>> + * its children or threads, just set TIF_MEMDIE so it can die quickly
>> + */
>> + if (p->flags & PF_EXITING) {
>> + set_tsk_thread_flag(p, TIF_MEMDIE);
>> + put_task_struct(p);
>> + read_unlock(&tasklist_lock);
>> + return;
>> + }
>> do {
>> list_for_each_entry(child, &t->children, sibling) {
>> unsigned int child_points;
>> --
>> 1.7.4.1
>>
>
Hi Johannes,
thank you very much! Fortunately, i didn't notice anything like this yet.
azur
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