linux-kernel - Re: [PATCH -next] cgroup/cpuset: Do not clear xcpus when clearing cpus

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Message-ID: <6a79b50a-ad74-4b1b-a98c-7da8ef341b24@redhat.com>
Date: Wed, 31 Jul 2024 23:22:44 -0400
From: Waiman Long <longman@...hat.com>
To: Chen Ridong <chenridong@...wei.com>, tj@...nel.org,
 lizefan.x@...edance.com, hannes@...xchg.org, adityakali@...gle.com,
 sergeh@...nel.org
Cc: bpf@...r.kernel.org, cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next] cgroup/cpuset: Do not clear xcpus when clearing
 cpus

On 7/31/24 05:21, Chen Ridong wrote:
> After commit 737bb142a00d ("cgroup/cpuset: Make cpuset.cpus.exclusive
> independent of cpuset.cpus"), cpuset.cpus.exclusive and cpuset.cpus
> became independent. However we found that cpuset.cpus.exclusive.effective
> is cleared when cpuset.cpus is clear. To fix this issue, just remove xcpus
> clearing when cpuset.cpus is being cleared.
>
> It can be reproduced as below:
> cd /sys/fs/cgroup/
> mkdir test
> echo +cpuset > cgroup.subtree_control
> cd test
> echo 3 > cpuset.cpus.exclusive
> cat cpuset.cpus.exclusive.effective
> 3
> echo > cpuset.cpus
> cat cpuset.cpus.exclusive.effective // was cleared
>
> Signed-off-by: Chen Ridong <chenridong@...wei.com>
> ---
>   kernel/cgroup/cpuset.c | 5 ++---
>   1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index a9b6d56eeffa..248c39bebbe9 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -2523,10 +2523,9 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
>   	 * that parsing.  The validate_change() call ensures that cpusets
>   	 * with tasks have cpus.
>   	 */
> -	if (!*buf) {
> +	if (!*buf)
>   		cpumask_clear(trialcs->cpus_allowed);
> -		cpumask_clear(trialcs->effective_xcpus);
> -	} else {
> +	else {
>   		retval = cpulist_parse(buf, trialcs->cpus_allowed);
>   		if (retval < 0)
>   			return retval;

Yes, that is a corner case bug that has not been properly handled.

Reviewed-by: Waiman Long <longman@...hat.com>