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.
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