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

[chenjinghuang <chenjinghuang2@huawei.com>]

On 8/4/2026 4:44 PM, K Prateek Nayak wrote:
> 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 Prateek, I'll update the patch accordingly.