Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
index 009cdf3..7aef0ab 100644
--- a/include/linux/percpu-refcount.h
+++ b/include/linux/percpu-refcount.h
@@ -75,14 +75,21 @@
 	 * operation using percpu_ref_switch_to_percpu().  If initialized
 	 * with this flag, the ref will stay in atomic mode until
 	 * percpu_ref_switch_to_percpu() is invoked on it.
+	 * Implies ALLOW_REINIT.
 	 */
 	PERCPU_REF_INIT_ATOMIC	= 1 << 0,
 
 	/*
 	 * Start dead w/ ref == 0 in atomic mode.  Must be revived with
-	 * percpu_ref_reinit() before used.  Implies INIT_ATOMIC.
+	 * percpu_ref_reinit() before used.  Implies INIT_ATOMIC and
+	 * ALLOW_REINIT.
 	 */
 	PERCPU_REF_INIT_DEAD	= 1 << 1,
+
+	/*
+	 * Allow switching from atomic mode to percpu mode.
+	 */
+	PERCPU_REF_ALLOW_REINIT	= 1 << 2,
 };
 
 struct percpu_ref {
@@ -95,6 +102,7 @@
 	percpu_ref_func_t	*release;
 	percpu_ref_func_t	*confirm_switch;
 	bool			force_atomic:1;
+	bool			allow_reinit:1;
 	struct rcu_head		rcu;
 };
 
@@ -108,6 +116,7 @@
 void percpu_ref_switch_to_percpu(struct percpu_ref *ref);
 void percpu_ref_kill_and_confirm(struct percpu_ref *ref,
 				 percpu_ref_func_t *confirm_kill);
+void percpu_ref_resurrect(struct percpu_ref *ref);
 void percpu_ref_reinit(struct percpu_ref *ref);
 
 /**