From 1fd4224a6b641f1949e27bf350b5b1c1e47e2ccc Mon Sep 17 00:00:00 2001 From: John Ogness Date: Wed, 16 Nov 2022 17:27:33 +0106 Subject: [PATCH] console: introduce console_is_registered() 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 Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20221116162152.193147-22-john.ogness@linutronix.de --- include/linux/console.h | 28 ++++++++++++++++++++++++++++ kernel/printk/printk.c | 2 +- 2 files changed, 29 insertions(+), 1 deletion(-) diff --git a/include/linux/console.h b/include/linux/console.h index c1ca461d088aa..f716e1dd9eaf2 100644 --- a/include/linux/console.h +++ b/include/linux/console.h @@ -228,6 +228,34 @@ static inline void console_srcu_write_flags(struct console *con, short 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); +} + +/* + * 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 101d08d9dc880..e58a6ccb945ca 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -3443,7 +3443,7 @@ static int unregister_console_locked(struct console *console) /* Disable it unconditionally */ console_srcu_write_flags(console, console->flags & ~CON_ENABLED); - if (hlist_unhashed(&console->node)) { + if (!console_is_registered_locked(console)) { console_unlock(); return -ENODEV; } -- 2.30.2