diff mbox series

[printk,v3,22/40] console: introduce console_is_registered()

Message ID 20221107141638.3790965-23-john.ogness@linutronix.de
State New
Headers
Series reduce console_lock scope |

Commit Message

John Ogness Nov. 7, 2022, 2:16 p.m. UTC 
  Currently it is not possible for drivers to detect if they have
already successfully registered their console. Several drivers
have multiple paths that lead to console registration. To avoid
attempting a 2nd registration (which leads to a WARN), drivers
are implementing their own solution.

Introduce console_is_registered() so drivers can easily identify
if their console is currently registered. A _locked() variant
is also provided if the caller is already holding the
console_list_lock.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
 include/linux/console.h | 28 ++++++++++++++++++++++++++++
 kernel/printk/printk.c  |  2 +-
 2 files changed, 29 insertions(+), 1 deletion(-)

Comments

Petr Mladek Nov. 10, 2022, 1 p.m. UTC | #1 
On Mon 2022-11-07 15:22:20, John Ogness wrote:
> Currently it is not possible for drivers to detect if they have
> already successfully registered their console. Several drivers
> have multiple paths that lead to console registration. To avoid
> attempting a 2nd registration (which leads to a WARN), drivers
> are implementing their own solution.
> 
> Introduce console_is_registered() so drivers can easily identify
> if their console is currently registered. A _locked() variant
> is also provided if the caller is already holding the
> console_list_lock.
> 
> Signed-off-by: John Ogness <john.ogness@linutronix.de>

Reviewed-by: Petr Mladek <pmladek@suse.com>

Best Regards,
Petr
diff mbox series

Patch

diff --git a/include/linux/console.h b/include/linux/console.h
index 47be23be8a88..cdae70e27377 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -210,6 +210,34 @@  static inline bool console_is_enabled(const struct console *con)
 	return (data_race(READ_ONCE(con->flags)) & CON_ENABLED);
 }
 
+/* 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);
+}
+
+/*
+ * 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
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 31387ba3fa1a..be40a9688403 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3410,7 +3410,7 @@  static int unregister_console_locked(struct console *console)
 	/* Disable it unconditionally */
 	WRITE_ONCE(console->flags, console->flags & ~CON_ENABLED);
 
-	if (hlist_unhashed(&console->node)) {
+	if (!console_is_registered_locked(console)) {
 		console_unlock();
 		return -ENODEV;
 	}