Re: [PATCH v6 08/10] fs/resctrl: Prevent deadlock and use-after-free in info file handlers

[Reinette Chatre]

Hi Tony,

On 7/7/26 4:33 PM, Luck, Tony wrote:
> On Mon, Jul 06, 2026 at 03:46:28PM -0700, Reinette Chatre wrote:
>> @@ -1020,9 +1030,15 @@ static int rdt_min_cbm_bits_show(struct kernfs_open_file *of,
>>  				 struct seq_file *seq, void *v)
>>  {
>>  	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);
>> -	struct rdt_resource *r = s->res;
>> +	struct rdt_resource *r;
>> +
> 
> Extra blank line added here.
>>  
>> +	if (!info_kn_lock(of->kn))
>> +		return -ENOENT;
>> +	r = s->res;
>>  	seq_printf(seq, "%u\n", r->cache.min_cbm_bits);
>> +	info_kn_unlock(of->kn);
>> +
>>  	return 0;
>>  }
>>  
> 
> ...
> 
>> @@ -1652,8 +1718,8 @@ static int mbm_config_show(struct seq_file *s, struct rdt_resource *r, u32 evtid
>>  	struct rdt_l3_mon_domain *dom;
>>  	bool sep = false;
>>  
>> -	cpus_read_lock();
>> -	mutex_lock(&rdtgroup_mutex);
>> +	lockdep_assert_cpus_held();
>> +	lockdep_assert_held(&rdtgroup_mutex);
>>  
>>  	list_for_each_entry_rcu(dom, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
>>  		if (sep)
>> @@ -1670,8 +1736,6 @@ static int mbm_config_show(struct seq_file *s, struct rdt_resource *r, u32 evtid
>>  	}
>>  	seq_puts(s, "\n");
>>  
>> -	mutex_unlock(&rdtgroup_mutex);
>> -	cpus_read_unlock();
>>  
> 
> Extra blank line here after deleting those two lines.
> 
Thank you very much. I plan to send a new version of this series based on -rc3 next week unless
I learn about a better way to handle this before then.

Reinette