1 files changed, 124 insertions, 5 deletions

diff --git a/include/linux/console.h b/include/linux/console.h
index 8c1686e2c233..9cea254b34b8 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -15,6 +15,7 @@
 #define _LINUX_CONSOLE_H_ 1
 
 #include <linux/atomic.h>
+#include <linux/rculist.h>
 #include <linux/types.h>
 
 struct vc_data;
@@ -154,14 +155,132 @@ struct console {
 	u64	seq;
 	unsigned long dropped;
 	void	*data;
-	struct	 console *next;
+	struct hlist_node node;
 };
 
+#ifdef CONFIG_LOCKDEP
+extern void lockdep_assert_console_list_lock_held(void);
+#else
+static inline void lockdep_assert_console_list_lock_held(void)
+{
+}
+#endif
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+extern bool console_srcu_read_lock_is_held(void);
+#else
+static inline bool console_srcu_read_lock_is_held(void)
+{
+	return 1;
+}
+#endif
+
+extern int console_srcu_read_lock(void);
+extern void console_srcu_read_unlock(int cookie);
+
+extern void console_list_lock(void) __acquires(console_mutex);
+extern void console_list_unlock(void) __releases(console_mutex);
+
+extern struct hlist_head console_list;
+
+/**
+ * console_srcu_read_flags - Locklessly read the console flags
+ * @con:	struct console pointer of console to read flags from
+ *
+ * This function provides the necessary READ_ONCE() and data_race()
+ * notation for locklessly reading the console flags. The READ_ONCE()
+ * in this function matches the WRITE_ONCE() when @flags are modified
+ * for registered consoles with console_srcu_write_flags().
+ *
+ * Only use this function to read console flags when locklessly
+ * iterating the console list via srcu.
+ *
+ * Context: Any context.
+ */
+static inline short console_srcu_read_flags(const struct console *con)
+{
+	WARN_ON_ONCE(!console_srcu_read_lock_is_held());
+
+	/*
+	 * Locklessly reading console->flags provides a consistent
+	 * read value because there is at most one CPU modifying
+	 * console->flags and that CPU is using only read-modify-write
+	 * operations to do so.
+	 */
+	return data_race(READ_ONCE(con->flags));
+}
+
+/**
+ * console_srcu_write_flags - Write flags for a registered console
+ * @con:	struct console pointer of console to write flags to
+ * @flags:	new flags value to write
+ *
+ * Only use this function to write flags for registered consoles. It
+ * requires holding the console_list_lock.
+ *
+ * Context: Any context.
+ */
+static inline void console_srcu_write_flags(struct console *con, short flags)
+{
+	lockdep_assert_console_list_lock_held();
+
+	/* This matches the READ_ONCE() in console_srcu_read_flags(). */
+	WRITE_ONCE(con->flags, flags);
+}
+
+/* Variant of console_is_registered() when the console_list_lock is held. */
+static inline bool console_is_registered_locked(const struct console *con)
+{
+	lockdep_assert_console_list_lock_held();
+	return !hlist_unhashed(&con->node);
+}
+
 /*
- * for_each_console() allows you to iterate on each console
+ * console_is_registered - Check if the console is registered
+ * @con:	struct console pointer of console to check
+ *
+ * Context: Process context. May sleep while acquiring console list lock.
+ * Return: true if the console is in the console list, otherwise false.
+ *
+ * If false is returned for a console that was previously registered, it
+ * can be assumed that the console's unregistration is fully completed,
+ * including the exit() callback after console list removal.
+ */
+static inline bool console_is_registered(const struct console *con)
+{
+	bool ret;
+
+	console_list_lock();
+	ret = console_is_registered_locked(con);
+	console_list_unlock();
+	return ret;
+}
+
+/**
+ * for_each_console_srcu() - Iterator over registered consoles
+ * @con:	struct console pointer used as loop cursor
+ *
+ * Although SRCU guarantees the console list will be consistent, the
+ * struct console fields may be updated by other CPUs while iterating.
+ *
+ * Requires console_srcu_read_lock to be held. Can be invoked from
+ * any context.
+ */
+#define for_each_console_srcu(con)					\
+	hlist_for_each_entry_srcu(con, &console_list, node,		\
+				  console_srcu_read_lock_is_held())
+
+/**
+ * for_each_console() - Iterator over registered consoles
+ * @con:	struct console pointer used as loop cursor
+ *
+ * The console list and the console->flags are immutable while iterating.
+ *
+ * Requires console_list_lock to be held.
  */
-#define for_each_console(con) \
-	for (con = console_drivers; con != NULL; con = con->next)
+#define for_each_console(con)						\
+	lockdep_assert_console_list_lock_held();			\
+	hlist_for_each_entry(con, &console_list, node)
 
 extern int console_set_on_cmdline;
 extern struct console *early_console;
@@ -172,9 +291,9 @@ enum con_flush_mode {
 };
 
 extern int add_preferred_console(char *name, int idx, char *options);
+extern void console_force_preferred_locked(struct console *con);
 extern void register_console(struct console *);
 extern int unregister_console(struct console *);
-extern struct console *console_drivers;
 extern void console_lock(void);
 extern int console_trylock(void);
 extern void console_unlock(void);