Re: [PATCH 2/2] cgroup/cpuset: Fix invalid local partition recovery

[Waiman Long <longman@redhat.com>]

On 10/10/26 3:59 AM, Guopeng Zhang wrote:
> From: Guopeng Zhang <zhangguopeng@kylinos.cn>
>
> An invalid local partition may fail to recover after its exclusive CPU
> list is changed to a valid one.
>
> This can be reproduced on a cgroup v2 system with CPUs 0-7 online:
>
>      cd /sys/fs/cgroup
>      echo +cpuset > cgroup.subtree_control
>      mkdir A
>      echo 0-7 > A/cpuset.cpus
>      echo 0-7 > A/cpuset.cpus.exclusive
>      echo root > A/cpuset.cpus.partition
>      cat A/cpuset.cpus.partition
>      echo 1 > A/cpuset.cpus.exclusive
>      cat A/cpuset.cpus.partition
>
> The first read reports root invalid because all CPUs were requested.
> After the mask is changed to CPU 1, the partition should become valid,
> but it remains invalid with PERR_NOCPUS.
>
> update_exclusive_cpumask() calls partition_cpus_change() before updating
> cs->exclusive_cpus. update_parent_effective_cpumask() then gets the
> old 0-7 mask from user_xcpus() and sets PERR_NOCPUS even though the new
> mask leaves CPUs for the parent.
>
> Move the exclusive_cpus update before partition_cpus_change() so that
> the partition update sees the new mask.
>
> Fixes: 46c521bac592 ("cgroup/cpuset: Enable invalid to valid local partition transition")
> Signed-off-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
> ---
>   kernel/cgroup/cpuset.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index de7553459adc..e96bc66ffa07 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -2546,10 +2546,14 @@ static int update_exclusive_cpumask(struct cpuset *cs, struct cpuset *trialcs,
>   		return -ENOMEM;
>   
>   	trialcs->prs_err = PERR_NONE;
> -	partition_cpus_change(cs, trialcs, &tmp);
>   
>   	spin_lock_irq(&callback_lock);
>   	cpumask_copy(cs->exclusive_cpus, trialcs->exclusive_cpus);
> +	spin_unlock_irq(&callback_lock);
> +
> +	partition_cpus_change(cs, trialcs, &tmp);
> +
> +	spin_lock_irq(&callback_lock);
>   	cpumask_copy(cs->effective_xcpus, trialcs->effective_xcpus);
>   	if ((old_prs > 0) && !is_partition_valid(cs))
>   		reset_partition_data(cs);

With the patch series that I have just sent out, I can't reproduce this 
problem. My patch 2 of the series change 
update_parent_effective_cpumask() to not use user_xcpus() anymore. So 
that should fix the problem.

Cheers, Longman