linux-kernel - Re: [PATCH] cgroup: fixed the cset refcnt leak when fork() failed

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Date:   Mon, 5 Jun 2023 10:51:50 -0400
From:   Waiman Long <longman@...hat.com>
To:     Zou Cao <zoucaox@...il.com>, linux-kernel@...r.kernel.org,
        tj@...nel.org
Cc:     cgroups@...r.kernel.org, lizefan.x@...edance.com,
        hannes@...xchg.org, brauner@...nel.org,
        Zou Cao <zoucao@...ishou.com>
Subject: Re: [PATCH] cgroup: fixed the cset refcnt leak when fork() failed


On 6/5/23 10:12, Waiman Long wrote:
>> kernel/cgroup/cgroup.c | 5 +++++
>>   1 file changed, 5 insertions(+)
>>
>> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
>> index d18c2ef..5ecd706 100644
>> --- a/kernel/cgroup/cgroup.c
>> +++ b/kernel/cgroup/cgroup.c
>> @@ -6284,6 +6284,11 @@ void cgroup_cancel_fork(struct task_struct 
>> *child,
>>           if (ss->cancel_fork)
>>               ss->cancel_fork(child, kargs->cset);
>>   +    if (!(kargs->flags & CLONE_INTO_CGROUP) &&
>> +            kargs->cset) {
>> +        put_css_set(kargs->cset);
>> +    }
>> +
> I believe the out_revert error path of cgroup_can_fork() has a similar 
> issue. Perhaps you may want to put the put_css_set() call in 
> cgroup_css_set_put_fork().

Sorry, it should not be done in cgroup_css_set_put_fork(). As the 
increase in reference is properly matched in css_post_fork(). That means 
similar change will be needed in cgroup_can_fork().

Cheers,
Longman