Re: [PATCH v6 02/24] x86/resctrl: kfree() rmid_ptrs from rdtgroup_exit()

James Morse
2023-10-05T17:15:56Z

Hi Babu,

On 04/10/2023 19:00, Moger, Babu wrote:
> On 9/14/23 12:21, James Morse wrote:
>> rmid_ptrs[] is allocated from dom_data_init() but never free()d.
>>
>> While the exit text ends up in the linker script's DISCARD section,
>> the direction of travel is for resctrl to be/have loadable modules.
>>
>> Add resctrl_exit_mon_l3_config() to cleanup any memory allocated
>> by rdt_get_mon_l3_config().
>>
>> There is no reason to backport this to a stable kernel.

>> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
>> index 85ceaf9a31ac..57cf1e6a57bd 100644
>> --- a/arch/x86/kernel/cpu/resctrl/internal.h
>> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
>> @@ -537,6 +537,7 @@ void closid_free(int closid);
>> int alloc_rmid(void);
>> void free_rmid(u32 rmid);
>> int rdt_get_mon_l3_config(struct rdt_resource *r);
>> +void resctrl_exit_mon_l3_config(struct rdt_resource *r);
>> bool __init rdt_cpu_has(int flag);
>> void mon_event_count(void *info);
>> int rdtgroup_mondata_show(struct seq_file *m, void *arg);
>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
>> index ded1fc7cb7cb..cfb3f632a4b2 100644
>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>> @@ -741,6 +741,16 @@ static int dom_data_init(struct rdt_resource *r)
>> return 0;
>> }
>>
>> +void resctrl_exit_mon_l3_config(struct rdt_resource *r)
>> +{
>> + mutex_lock(&rdtgroup_mutex);
>> +
>> + kfree(rmid_ptrs);
>> + rmid_ptrs = NULL;
>> +
>> + mutex_unlock(&rdtgroup_mutex);
>> +}

> What is the need for passing "rdt_resource *r" here?

My vain belief that monitors should be supported on something other than L3, but I agree
that isn't what resctrl does today. I'll remove it.

> Is mutex_lock required?

Reads and writes to rmid_ptrs[] are protected by that lock. This ensures no-one reads the
value while its being free()d, and after this function releases the lock, anyone trying
sees NULL.

(This is all moot as its only caller is marked __exit, so gets discarded by the linker)

Thanks,

James