linux-kernel - Re: [PATCH -next] cgroup/pids: Remove unreachable paths of pids_{can,cancel}

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Message-ID: <309c8d74-a51f-42f7-b526-f5e74c0ac22c@redhat.com>
Date: Sat, 3 Aug 2024 09:59:03 -0400
From: Waiman Long <longman@...hat.com>
To: Xiu Jianfeng <xiujianfeng@...weicloud.com>, tj@...nel.org,
 lizefan.x@...edance.com, hannes@...xchg.org, mkoutny@...e.com
Cc: cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
 xiujianfeng@...wei.com
Subject: Re: [PATCH -next] cgroup/pids: Remove unreachable paths of
 pids_{can,cancel}_fork


On 8/3/24 02:16, Xiu Jianfeng wrote:
> From: Xiu Jianfeng <xiujianfeng@...wei.com>
>
> According to the implement of cgroup_css_set_fork() and the usage in
"implementation"?
> the cpuset controller which also has .can_fork and .cancel_fork hooks,
> the argument 'cset' for these two hooks must not be NULL, so remove
> the unrechable paths in thse two hooks.

It is primarily due to cgroup_css_set_fork() will fail if cset cannot be 
found and the can_fork/cancel_fork method will not be called in this case.

Cheers,
Longman

>
> Signed-off-by: Xiu Jianfeng <xiujianfeng@...wei.com>
> ---
>   kernel/cgroup/pids.c | 14 ++------------
>   1 file changed, 2 insertions(+), 12 deletions(-)
>
> diff --git a/kernel/cgroup/pids.c b/kernel/cgroup/pids.c
> index 34aa63d7c9c6..8f61114c36dd 100644
> --- a/kernel/cgroup/pids.c
> +++ b/kernel/cgroup/pids.c
> @@ -272,15 +272,10 @@ static void pids_event(struct pids_cgroup *pids_forking,
>    */
>   static int pids_can_fork(struct task_struct *task, struct css_set *cset)
>   {
> -	struct cgroup_subsys_state *css;
>   	struct pids_cgroup *pids, *pids_over_limit;
>   	int err;
>   
> -	if (cset)
> -		css = cset->subsys[pids_cgrp_id];
> -	else
> -		css = task_css_check(current, pids_cgrp_id, true);
> -	pids = css_pids(css);
> +	pids = css_pids(cset->subsys[pids_cgrp_id]);
>   	err = pids_try_charge(pids, 1, &pids_over_limit);
>   	if (err)
>   		pids_event(pids, pids_over_limit);
> @@ -290,14 +285,9 @@ static int pids_can_fork(struct task_struct *task, struct css_set *cset)
>   
>   static void pids_cancel_fork(struct task_struct *task, struct css_set *cset)
>   {
> -	struct cgroup_subsys_state *css;
>   	struct pids_cgroup *pids;
>   
> -	if (cset)
> -		css = cset->subsys[pids_cgrp_id];
> -	else
> -		css = task_css_check(current, pids_cgrp_id, true);
> -	pids = css_pids(css);
> +	pids = css_pids(cset->subsys[pids_cgrp_id]);
>   	pids_uncharge(pids, 1);
>   }
>