x86/resctrl: Factor rdtgroup lock for multi-file ops

rdtgroup_kn_lock_live() can only release a kernfs reference for a single
file before waiting on the rdtgroup_mutex, limiting its usefulness for
operations on multiple files, such as rename.

Factor the work needed to respectively break and unbreak active
protection on an individual file into rdtgroup_kn_{get,put}().

No functional change.

Signed-off-by: Peter Newman <peternewman@google.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Tested-by: Babu Moger <babu.moger@amd.com>
Link: https://lore.kernel.org/r/20230419125015.693566-2-peternewman@google.com

Author: Peter Newman

arch/x86/kernel/cpu/resctrl/rdtgroup.c

@@ -2305,15 +2305,34 @@ static struct rdtgroup *kernfs_to_rdtgroup(struct kernfs_node *kn)
 	}
 }
 
+static void rdtgroup_kn_get(struct rdtgroup *rdtgrp, struct kernfs_node *kn)
+{
+	atomic_inc(&rdtgrp->waitcount);
+	kernfs_break_active_protection(kn);
+}
+
+static void rdtgroup_kn_put(struct rdtgroup *rdtgrp, struct kernfs_node *kn)
+{
+	if (atomic_dec_and_test(&rdtgrp->waitcount) &&
+	    (rdtgrp->flags & RDT_DELETED)) {
+		if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKSETUP ||
+		    rdtgrp->mode == RDT_MODE_PSEUDO_LOCKED)
+			rdtgroup_pseudo_lock_remove(rdtgrp);
+		kernfs_unbreak_active_protection(kn);
+		rdtgroup_remove(rdtgrp);
+	} else {
+		kernfs_unbreak_active_protection(kn);
+	}
+}
+
 struct rdtgroup *rdtgroup_kn_lock_live(struct kernfs_node *kn)
 {
 	struct rdtgroup *rdtgrp = kernfs_to_rdtgroup(kn);
 
 	if (!rdtgrp)
 		return NULL;
 
-	atomic_inc(&rdtgrp->waitcount);
-	kernfs_break_active_protection(kn);
+	rdtgroup_kn_get(rdtgrp, kn);
 
 	mutex_lock(&rdtgroup_mutex);
 
@@ -2332,17 +2351,7 @@ void rdtgroup_kn_unlock(struct kernfs_node *kn)
 		return;
 
 	mutex_unlock(&rdtgroup_mutex);
-
-	if (atomic_dec_and_test(&rdtgrp->waitcount) &&
-	    (rdtgrp->flags & RDT_DELETED)) {
-		if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKSETUP ||
-		    rdtgrp->mode == RDT_MODE_PSEUDO_LOCKED)
-			rdtgroup_pseudo_lock_remove(rdtgrp);
-		kernfs_unbreak_active_protection(kn);
-		rdtgroup_remove(rdtgrp);
-	} else {
-		kernfs_unbreak_active_protection(kn);
-	}
+	rdtgroup_kn_put(rdtgrp, kn);
 }
 
 static int mkdir_mondata_all(struct kernfs_node *parent_kn,