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

[Jinjie Ruan]

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);
 }
 
-- 
2.34.1