Re: [PATCH] sched/numa: Prevent race on sysctl_numa_balancing static key

[K Prateek Nayak]

Hello Chen,

On 8/4/2026 2:05 PM, chenjinghuang wrote:
> You're right - my mistake, I'll move numabalancing_mutex into sysctl_numa_balancing()
> and drop it from the early-init path. No one races during init, so the lock is only
> needed for sysfs writes:
> 
> +static DEFINE_MUTEX(numabalancing_mutex);
> +
>  static int sysctl_numa_balancing(const struct ctl_table *table, int write,
>  			  void *buffer, size_t *lenp, loff_t *ppos)
>  {
> @@ -4666,11 +4668,13 @@ static int sysctl_numa_balancing(const struct ctl_table *table, int write,
>  	if (err < 0)
>  		return err;
>  	if (write) {
> +		mutex_lock(&numabalancing_mutex);

nit. You can just use a:

		guard(mutex)(&numabalancing_mutex); 

>  		if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING) &&
>  		    (state & NUMA_BALANCING_MEMORY_TIERING))
>  			reset_memory_tiering();
>  		sysctl_numa_balancing_mode = state;
>  		__set_numabalancing_state(state);
> +		mutex_unlock(&numabalancing_mutex);

... and save on the need to explicitly call unlock here.

>  	}
>  	return err;
>  }

-- 
Thanks and Regards,
Prateek