linux-kernel - Re: [PATCH -next] cgroup/pids: Avoid spurious event notification

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Message-ID: <cd074750-172f-89e6-f46b-45c808b84d06@huaweicloud.com>
Date: Tue, 30 Jul 2024 11:33:58 +0800
From: Xiu Jianfeng <xiujianfeng@...weicloud.com>
To: Michal Koutný <mkoutny@...e.com>
Cc: tj@...nel.org, lizefan.x@...edance.com, hannes@...xchg.org,
 cgroups@...r.kernel.org, linux-kernel@...r.kernel.org, xiujianfeng@...wei.com
Subject: Re: [PATCH -next] cgroup/pids: Avoid spurious event notification



On 2024/7/30 0:07, Michal Koutný wrote:
> Hello.
> 
> On Mon, Jul 29, 2024 at 10:58:24AM GMT, Xiu Jianfeng <xiujianfeng@...weicloud.com> wrote:
>> To address this issue, only the cgroups from 'pids_over_limit' to root
>> will have their PIDCG_MAX counter increased and event notifications
>> generated.
>>
> 
> For completeness here
> 
> Fixes: 385a635cacfe0 ("cgroup/pids: Make event counters hierarchical")>
>> Signed-off-by: Xiu Jianfeng <xiujianfeng@...wei.com>
>> ---
>>  kernel/cgroup/pids.c | 13 ++++---------
>>  1 file changed, 4 insertions(+), 9 deletions(-)
> 
> 
> 
>> @@ -257,15 +256,11 @@ static void pids_event(struct pids_cgroup *pids_forking,
>>  	    cgrp_dfl_root.flags & CGRP_ROOT_PIDS_LOCAL_EVENTS)
>>  		return;
>>  
>> -	for (; parent_pids(p); p = parent_pids(p)) {
>> -		if (p == pids_over_limit) {
>> -			limit = true;
>> -			atomic64_inc(&p->events_local[PIDCG_MAX]);
>> -			cgroup_file_notify(&p->events_local_file);
>> -		}
>> -		if (limit)
>> -			atomic64_inc(&p->events[PIDCG_MAX]);
>> +	atomic64_inc(&pids_over_limit->events_local[PIDCG_MAX]);
>> +	cgroup_file_notify(&pids_over_limit->events_local_file);
>>  
>> +	for (p = pids_over_limit; parent_pids(p); p = parent_pids(p)) {
>> +		atomic64_inc(&p->events[PIDCG_MAX]);
>>  		cgroup_file_notify(&p->events_file);
>>  	}
> 
> When I look at it applied altogther, there's one extra notification
> (heritage of forkfail events), it should be fixed with:
> 
> --- a/kernel/cgroup/pids.c
> +++ b/kernel/cgroup/pids.c
> @@ -251,10 +251,11 @@ static void pids_event(struct pids_cgroup *pids_forking,
>                 pr_cont_cgroup_path(p->css.cgroup);
>                 pr_cont("\n");
>         }
> -       cgroup_file_notify(&p->events_local_file);
>         if (!cgroup_subsys_on_dfl(pids_cgrp_subsys) ||
> -           cgrp_dfl_root.flags & CGRP_ROOT_PIDS_LOCAL_EVENTS)
> +           cgrp_dfl_root.flags & CGRP_ROOT_PIDS_LOCAL_EVENTS) {
> +               cgroup_file_notify(&p->events_local_file);
>                 return;
> +       }

Thanks, looks good, will do in the next version.

>  
>         atomic64_inc(&pids_over_limit->events_local[PIDCG_MAX]);
>         cgroup_file_notify(&pids_over_limit->events_local_file);
> 
> Besides that it makes sense to me.
> 
> Thanks,
> Michal