[PATCH v10 06/15] fs/resctrl: Unmount resctrl with the CDP state it was mounted with

[Jinjie Ruan]

From: Zeng Heng <zengheng4@xxxxxxxxxx>

resctrl disables CDP before the control and monitor groups are torn down
on unmount. The architecture translates between CLOSID and PARTID using
the CDP state, so the RMIDs freed by rmdir_all_sub() and
resctrl_fs_teardown() are parsed with the wrong mapping. On arm64 the
RMID limbo handler can still be running, and a CLOSID left in the limbo
list is re-interpreted with the CDP state of the next mount. Enabling
CDP doubles the CLOSID on arm64, which can push the stale value out of
range and take an MPAM error interrupt.

Disable CDP after the groups have been torn down, so every CLOSID freed
on unmount is parsed with the CDP state it was allocated under. Return
the RMIDs still in limbo to the free list and stop the worker, so
nothing carries over to the next mount.

Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: Reinette Chatre <reinette.chatre@xxxxxxxxx>
Cc: Dave Martin <Dave.Martin@xxxxxxx>
Cc: James Morse <james.morse@xxxxxxx>
Cc: Babu Moger <babu.moger@xxxxxxx>
Signed-off-by: Zeng Heng <zengheng4@xxxxxxxxxx>
Signed-off-by: Jinjie Ruan <ruanjinjie@xxxxxxxxxx>
---
v9->v10:
 - Use cancel_delayed_work_sync() with proper mutex handling
 - Add comment explaining the lock pattern
---
 fs/resctrl/rdtgroup.c | 46 +++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 44 insertions(+), 2 deletions(-)

diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index 5dcbb0a964e8..40821cf07649 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -3145,6 +3145,41 @@ static void resctrl_fs_teardown(void)
 	rdtgroup_destroy_root();
 }
 
+/*
+ * The RMID limbo handler keeps running after unmount. Any CLOSID still in
+ * limbo would be re-interpreted with the CDP state of the next mount. MPAM
+ * doubles CLOSID when CDP is enabled, which can push the stale value out of
+ * range. Force the limbo list back to the free list before the CLOSID state
+ * is torn down.
+ */
+static void rdt_flush_limbo(void)
+{
+	struct rdt_resource *r = resctrl_arch_get_resource(RDT_RESOURCE_L3);
+	struct rdt_l3_mon_domain *d;
+
+	if (!IS_ENABLED(CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID))
+		return;
+
+	if (!resctrl_is_mon_event_enabled(QOS_L3_OCCUP_EVENT_ID))
+		return;
+
+	list_for_each_entry(d, &r->mon_domains, hdr.list) {
+		if (!has_busy_rmid(d))
+			continue;
+
+		/*
+		 * The limbo handler acquires rdtgroup_mutex. Release it
+		 * here to allow the handler to complete, then reacquire
+		 * to maintain lock ordering for __check_limbo().
+		 * This matches the pattern used in resctrl_offline_cpu().
+		 */
+		mutex_unlock(&rdtgroup_mutex);
+		cancel_delayed_work_sync(&d->cqm_limbo);
+		mutex_lock(&rdtgroup_mutex);
+		__check_limbo(d, true);
+	}
+}
+
 static void resctrl_unmount(void)
 {
 	struct rdt_resource *r;
@@ -3152,13 +3187,20 @@ static void resctrl_unmount(void)
 	cpus_read_lock();
 	mutex_lock(&rdtgroup_mutex);
 
-	rdt_disable_ctx();
-
 	/* Put everything back to default values. */
 	for_each_alloc_capable_rdt_resource(r)
 		resctrl_arch_reset_all_ctrls(r);
 
 	resctrl_fs_teardown();
+	rdt_flush_limbo();
+
+	/*
+	 * Clear the CDP state last. free_rmid() translates between CLOSID and
+	 * PARTID using the CDP state; clearing it first would make the
+	 * translation inconsistent for the RMIDs being torn down.
+	 */
+	rdt_disable_ctx();
+
 	if (resctrl_arch_alloc_capable())
 		resctrl_arch_disable_alloc();
 	if (resctrl_arch_mon_capable())
-- 
2.43.0