futex: Create private_hash() get/put class

This gets us:

  fph = futex_private_hash(key) /* gets fph and inc users */
  futex_private_hash_get(fph)   /* inc users */
  futex_private_hash_put(fph)   /* dec users */

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: Peter Zijlstra

kernel/futex/core.c

@@ -107,6 +107,18 @@ late_initcall(fail_futex_debugfs);
 
 #endif /* CONFIG_FAIL_FUTEX */
 
+struct futex_private_hash *futex_private_hash(void)
+{
+	return NULL;
+}
+
+bool futex_private_hash_get(struct futex_private_hash *fph)
+{
+	return false;
+}
+
+void futex_private_hash_put(struct futex_private_hash *fph) { }
+
 /**
  * futex_hash - Return the hash bucket in the global hash
  * @key:	Pointer to the futex key for which the hash is calculated

kernel/futex/futex.h

@@ -206,10 +206,18 @@ extern struct futex_hash_bucket *futex_hash(union futex_key *key);
 extern void futex_hash_get(struct futex_hash_bucket *hb);
 extern void futex_hash_put(struct futex_hash_bucket *hb);
 
+extern struct futex_private_hash *futex_private_hash(void);
+extern bool futex_private_hash_get(struct futex_private_hash *fph);
+extern void futex_private_hash_put(struct futex_private_hash *fph);
+
 DEFINE_CLASS(hb, struct futex_hash_bucket *,
 	     if (_T) futex_hash_put(_T),
 	     futex_hash(key), union futex_key *key);
 
+DEFINE_CLASS(private_hash, struct futex_private_hash *,
+	     if (_T) futex_private_hash_put(_T),
+	     futex_private_hash(), void);
+
 /**
  * futex_match - Check whether two futex keys are equal
  * @key1:	Pointer to key1