Re: [PATCH v10 RESEND 02/15] fs/resctrl: Skip monitor context allocation when force-freeing RMIDs

[Ben Horgan <ben.horgan@arm.com>]

Hi Jinjie,

On 26/10/2026 14:08, Ben Horgan wrote:
> Hi Jinjie,
> 
> On 20/10/2026 14:42, Jinjie Ruan wrote:
>> __check_limbo() allocates the architecture monitor context before the
>> scan loop, even when force_free is set. The force-free path never reads
>> occupancy and never uses the context.
>>
>> If the allocation fails, the function returns early and leaves the limbo
>> list unflushed. Callers such as the unmount path then silently fail to
>> return the RMIDs to the free list, leaving stale CLOSIDs in limbo that
>> are re-interpreted with the CDP state of the next mount.
> 
> Is this a theoretical fix or is there some way that resctrl_arch_mon_ctx_alloc() can fail in practice?

This does seem a good change to me and we do have to consider that the memory alocation might fail.

Thanks,

Ben

> 
> Thanks,
> 
> Ben
> 
>>
>> Only allocate and free the monitor context when occupancy will be read.
>>
>> Fixes: fa7d949337cc ("x86/resctrl: Rename and move rdt files to a separate directory")
>> Cc: James Morse <james.morse@arm.com>
>> Cc: Reinette Chatre <reinette.chatre@intel.com>
>> Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
>> ---
>>  fs/resctrl/monitor.c | 15 +++++++++------
>>  1 file changed, 9 insertions(+), 6 deletions(-)
>>
>> diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
>> index da883adc3adc..ffa9c67c9f00 100644
>> --- a/fs/resctrl/monitor.c
>> +++ b/fs/resctrl/monitor.c
>> @@ -142,11 +142,13 @@ void __check_limbo(struct rdt_l3_mon_domain *d, bool force_free)
>>  	u64 val = 0;
>>  
>>  	arch_priv = mon_event_all[QOS_L3_OCCUP_EVENT_ID].arch_priv;
>> -	arch_mon_ctx = resctrl_arch_mon_ctx_alloc(r, QOS_L3_OCCUP_EVENT_ID);
>> -	if (IS_ERR(arch_mon_ctx)) {
>> -		pr_warn_ratelimited("Failed to allocate monitor context: %pe",
>> -				    arch_mon_ctx);
>> -		return;
>> +	if (!force_free) {
>> +		arch_mon_ctx = resctrl_arch_mon_ctx_alloc(r, QOS_L3_OCCUP_EVENT_ID);
>> +		if (IS_ERR(arch_mon_ctx)) {
>> +			pr_warn_ratelimited("Failed to allocate monitor context: %pe",
>> +					    arch_mon_ctx);
>> +			return;
>> +		}
>>  	}
>>  
>>  	/*
>> @@ -192,7 +194,8 @@ void __check_limbo(struct rdt_l3_mon_domain *d, bool force_free)
>>  		cur_idx = idx + 1;
>>  	}
>>  
>> -	resctrl_arch_mon_ctx_free(r, QOS_L3_OCCUP_EVENT_ID, arch_mon_ctx);
>> +	if (!force_free)
>> +		resctrl_arch_mon_ctx_free(r, QOS_L3_OCCUP_EVENT_ID, arch_mon_ctx);
>>  }
>>  
>>  bool has_busy_rmid(struct rdt_l3_mon_domain *d)
>