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 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?

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)