Re: [PATCH v10 RESEND 01/15] fs/resctrl: Return -EBUSY when per-CLOSID RMIDs are in limbo

[Reinette Chatre]

Hi Jinjie,

On 10/20/26 6:42 AM, Jinjie Ruan wrote:
> resctrl_find_free_rmid() returns ERR_PTR(-ENOSPC) when no matching RMID
> is found in the free list. On systems where RMIDs depend on CLOSIDs
> (CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID), the target CLOSID may have RMIDs
> temporarily in limbo rather than permanently exhausted.
> 
> When userspace attempts to create a new monitoring group, a permanent
> -ENOSPC failure prevents retry even though the CLOSID's RMIDs may become
> available once the limbo handler completes.
> 
> Check closid_num_dirty_rmid[] before returning -ENOSPC. If the target
> CLOSID has dirty RMIDs, return -EBUSY to signal a retryable condition.
> 
> Fixes: c4c0376eefe1 ("x86/resctrl: Allow RMID allocation to be scoped by CLOSID")
> Cc: James Morse <james.morse@xxxxxxx>
> Cc: Reinette Chatre <reinette.chatre@xxxxxxxxx>
> Cc: Babu Moger <babu.moger@xxxxxxx>
> Signed-off-by: Jinjie Ruan <ruanjinjie@xxxxxxxxxx>
> ---
>  fs/resctrl/monitor.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
> index 73413cb128ea..da883adc3adc 100644
> --- a/fs/resctrl/monitor.c
> +++ b/fs/resctrl/monitor.c
> @@ -225,6 +225,14 @@ static struct rmid_entry *resctrl_find_free_rmid(u32 closid)
>  			return itr;
>  	}
>  
> +	/*
> +	 * If this CLOSID has RMIDs in limbo, return -EBUSY so userspace can
> +	 * retry. Otherwise, the CLOSID is genuinely out of RMIDs.
> +	 */
> +	if (IS_ENABLED(CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID) &&
> +	    closid_num_dirty_rmid[closid])
> +		return ERR_PTR(-EBUSY);
> +
>  	return ERR_PTR(-ENOSPC);
>  }
>  

Does this address all scenarios? Consider for example the first test of 
resctrl_find_free_rmid():

	if (list_empty(&rmid_free_lru))
		return rmid_limbo_count ? ERR_PTR(-EBUSY) : ERR_PTR(-ENOSPC);

If rmid_free_lru is empty but rmid_limbo_count > 0 then it will return -EBUSY
but it may be that closid_num_dirty_rmid[closid] is zero so no amount of
waiting on limbo handler will produce a usable RMID.

Reinette