[PATCH v3 6/9] fs/resctrl: Add rmid_entry state helpers

[Zeng Heng]

Introduce helper functions for rmid_entry management, in preparation
for upcoming patches supporting dynamic monitoring group allocation:

* rmid_is_occupied(): Query whether a rmid_entry is currently allocated
  by checking if its list node has been removed from the free list.

* rmid_entry_reassign_closid(): Update the closid associated with a rmid
  entry.

Fix list node initialization in alloc_rmid() and dom_data_init() by
using list_del_init() instead of list_del(). This ensures list_empty()
checks in rmid_is_occupied() work correctly without encountering
LIST_POISON values.

Signed-off-by: Zeng Heng <zengheng4@xxxxxxxxxx>
---
 fs/resctrl/monitor.c    | 18 ++++++++++++++++--
 include/linux/resctrl.h | 21 +++++++++++++++++++++
 2 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
index 49f3f6b846b2..4e78fb194c16 100644
--- a/fs/resctrl/monitor.c
+++ b/fs/resctrl/monitor.c
@@ -284,7 +284,7 @@ int alloc_rmid(u32 closid)
 	if (IS_ERR(entry))
 		return PTR_ERR(entry);
 
-	list_del(&entry->list);
+	list_del_init(&entry->list);
 	return entry->rmid;
 }
 
@@ -344,6 +344,20 @@ void free_rmid(u32 closid, u32 rmid)
 		list_add_tail(&entry->list, &rmid_free_lru);
 }
 
+bool rmid_is_occupied(u32 closid, u32 rmid)
+{
+	u32 idx = resctrl_arch_rmid_idx_encode(closid, rmid);
+
+	return list_empty(&rmid_ptrs[idx].list);
+}
+
+void rmid_entry_reassign_closid(u32 closid, u32 rmid)
+{
+	u32 idx = resctrl_arch_rmid_idx_encode(closid, rmid);
+
+	rmid_ptrs[idx].closid = closid;
+}
+
 static struct mbm_state *get_mbm_state(struct rdt_l3_mon_domain *d, u32 closid,
 				       u32 rmid, enum resctrl_event_id evtid)
 {
@@ -943,7 +957,7 @@ int setup_rmid_lru_list(void)
 	idx = resctrl_arch_rmid_idx_encode(RESCTRL_RESERVED_CLOSID,
 					   RESCTRL_RESERVED_RMID);
 	entry = __rmid_entry(idx);
-	list_del(&entry->list);
+	list_del_init(&entry->list);
 
 	return 0;
 }
diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index 006e57fd7ca5..b636e7250c20 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -702,6 +702,27 @@ bool resctrl_arch_get_io_alloc_enabled(struct rdt_resource *r);
 extern unsigned int resctrl_rmid_realloc_threshold;
 extern unsigned int resctrl_rmid_realloc_limit;
 
+/**
+ * rmid_is_occupied() - Check whether the specified rmid has been
+ *                      allocated.
+ * @closid:	Specify the closid that matches the rmid.
+ * @rmid:	Specify the rmid entry to check status.
+ *
+ * This function checks if the rmid_entry is currently allocated by testing
+ * whether its list node is empty (removed from the free list).
+ *
+ * Return:
+ * True if the specified rmid is still in use.
+ */
+bool rmid_is_occupied(u32 closid, u32 rmid);
+
+/**
+ * rmid_entry_reassign_closid() - Update the closid field of a rmid_entry.
+ * @closid:	Specify the reassigned closid.
+ * @rmid:	Specify the rmid entry to update closid.
+ */
+void rmid_entry_reassign_closid(u32 closid, u32 rmid);
+
 int resctrl_init(void);
 void resctrl_exit(void);
 
-- 
2.25.1