On Wed, Nov 25, 2015 at 2:05 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
> On Tue, Nov 24, 2015 at 11:31 PM, Johannes Weiner <hannes@xxxxxxxxxxx> wrote:
>> Hi Dmitry,
>>
>> On Tue, Nov 24, 2015 at 02:50:26PM +0100, Dmitry Vyukov wrote:
>>> As a blind guess, I've added the following BUG into copy_process:
>>>
>>> diff --git a/kernel/fork.c b/kernel/fork.c
>>> index b4dc490..c5667e8 100644
>>> --- a/kernel/fork.c
>>> +++ b/kernel/fork.c
>>> @@ -1620,6 +1620,8 @@ static struct task_struct *copy_process(unsigned
>>> long clone_flags,
>>> trace_task_newtask(p, clone_flags);
>>> uprobe_copy_process(p, clone_flags);
>>>
>>> + BUG_ON(p->memcg_may_oom);
>>> +
>>> return p;
>>
>> Thanks for your report.
>>
>> I don't see how this could happen through the legitimate setters of
>> p->memcg_may_oom. Something must clobber it. What happens with the
>> following patch applied?
>>
>> diff --git a/include/linux/sched.h b/include/linux/sched.h
>> index edad7a4..42e1285 100644
>> --- a/include/linux/sched.h
>> +++ b/include/linux/sched.h
>> @@ -1463,9 +1463,11 @@ struct task_struct {
>> unsigned sched_reset_on_fork:1;
>> unsigned sched_contributes_to_load:1;
>> unsigned sched_migrated:1;
>> + unsigned dummy_a:1;
>> #ifdef CONFIG_MEMCG
>> unsigned memcg_may_oom:1;
>> #endif
>> + unsigned dummy_b:1;
>> #ifdef CONFIG_MEMCG_KMEM
>> unsigned memcg_kmem_skip_account:1;
>> #endif
>> diff --git a/kernel/fork.c b/kernel/fork.c
>> index f97f2c4..ab6f7ba 100644
>> --- a/kernel/fork.c
>> +++ b/kernel/fork.c
>> @@ -1617,6 +1617,12 @@ static struct task_struct *copy_process(unsigned long clone_flags,
>> trace_task_newtask(p, clone_flags);
>> uprobe_copy_process(p, clone_flags);
>>
>> + if (p->dummy_a || p->dummy_b || p->memcg_may_oom) {
>> + printk(KERN_ALERT "dummy_a:%d dummy_b:%d memcg_may_oom:%d\n",
>> + p->dummy_a, p->dummy_b, p->memcg_may_oom);
>> + BUG();
>> + }
>> +
>> return p;
>>
>> bad_fork_cancel_cgroup:
>
>
> I cannot reproduce the condition again, either with your patch or with
> mine patch... Will try harder.
I mean that I still can reproduce the original warning, but I can't
catch memcg_may_oom=1 in copy_process.
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