1 files changed, 44 insertions, 12 deletions

diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 4d6c6f5f60db83..d9c822bbffb8d3 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -113,9 +113,40 @@ int static_key_count(struct static_key *key)
 }
 EXPORT_SYMBOL_GPL(static_key_count);
 
-void static_key_slow_inc_cpuslocked(struct static_key *key)
+/*
+ * static_key_fast_inc_not_disabled - adds a user for a static key
+ * @key: static key that must be already enabled
+ *
+ * The caller must make sure that the static key can't get disabled while
+ * in this function. It doesn't patch jump labels, only adds a user to
+ * an already enabled static key.
+ *
+ * Returns true if the increment was done. Unlike refcount_t the ref counter
+ * is not saturated, but will fail to increment on overflow.
+ */
+bool static_key_fast_inc_not_disabled(struct static_key *key)
 {
+	int v;
+
 	STATIC_KEY_CHECK_USE(key);
+	/*
+	 * Negative key->enabled has a special meaning: it sends
+	 * static_key_slow_inc() down the slow path, and it is non-zero
+	 * so it counts as "enabled" in jump_label_update().  Note that
+	 * atomic_inc_unless_negative() checks >= 0, so roll our own.
+	 */
+	v = atomic_read(&key->enabled);
+	do {
+		if (v <= 0 || (v + 1) < 0)
+			return false;
+	} while (!likely(atomic_try_cmpxchg(&key->enabled, &v, v + 1)));
+
+	return true;
+}
+EXPORT_SYMBOL_GPL(static_key_fast_inc_not_disabled);
+
+bool static_key_slow_inc_cpuslocked(struct static_key *key)
+{
 	lockdep_assert_cpus_held();
 
 	/*
@@ -124,15 +155,9 @@ void static_key_slow_inc_cpuslocked(struct static_key *key)
 	 * jump_label_update() process.  At the same time, however,
 	 * the jump_label_update() call below wants to see
 	 * static_key_enabled(&key) for jumps to be updated properly.
-	 *
-	 * So give a special meaning to negative key->enabled: it sends
-	 * static_key_slow_inc() down the slow path, and it is non-zero
-	 * so it counts as "enabled" in jump_label_update().  Note that
-	 * atomic_inc_unless_negative() checks >= 0, so roll our own.
 	 */
-	for (int v = atomic_read(&key->enabled); v > 0; )
-		if (likely(atomic_try_cmpxchg(&key->enabled, &v, v + 1)))
-			return;
+	if (static_key_fast_inc_not_disabled(key))
+		return true;
 
 	jump_label_lock();
 	if (atomic_read(&key->enabled) == 0) {
@@ -144,16 +169,23 @@ void static_key_slow_inc_cpuslocked(struct static_key *key)
 		 */
 		atomic_set_release(&key->enabled, 1);
 	} else {
-		atomic_inc(&key->enabled);
+		if (WARN_ON_ONCE(!static_key_fast_inc_not_disabled(key))) {
+			jump_label_unlock();
+			return false;
+		}
 	}
 	jump_label_unlock();
+	return true;
 }
 
-void static_key_slow_inc(struct static_key *key)
+bool static_key_slow_inc(struct static_key *key)
 {
+	bool ret;
+
 	cpus_read_lock();
-	static_key_slow_inc_cpuslocked(key);
+	ret = static_key_slow_inc_cpuslocked(key);
 	cpus_read_unlock();
+	return ret;
 }
 EXPORT_SYMBOL_GPL(static_key_slow_inc);