From: Thomas Gleixner Date: Sat, 16 Sep 2023 21:26:07 +0206 Subject: [PATCH 082/134] printk: nbcon: Allow drivers to mark unsafe regions and check state Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz For the write_atomic callback, the console driver may have unsafe regions that need to be appropriately marked. Provide functions that accept the nbcon_write_context struct to allow for the driver to enter and exit unsafe regions. Also provide a function for drivers to check if they are still the owner of the console. Co-developed-by: John Ogness Signed-off-by: John Ogness Signed-off-by: Thomas Gleixner (Intel) Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20230916192007.608398-9-john.ogness@linutronix.de Signed-off-by: Sebastian Andrzej Siewior --- include/linux/console.h | 10 ++++++ kernel/printk/nbcon.c | 75 ++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 85 insertions(+) --- a/include/linux/console.h +++ b/include/linux/console.h @@ -451,6 +451,16 @@ static inline bool console_is_registered lockdep_assert_console_list_lock_held(); \ hlist_for_each_entry(con, &console_list, node) +#ifdef CONFIG_PRINTK +extern bool nbcon_can_proceed(struct nbcon_write_context *wctxt); +extern bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt); +extern bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt); +#else +static inline bool nbcon_can_proceed(struct nbcon_write_context *wctxt) { return false; } +static inline bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt) { return false; } +static inline bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt) { return false; } +#endif + extern int console_set_on_cmdline; extern struct console *early_console; --- a/kernel/printk/nbcon.c +++ b/kernel/printk/nbcon.c @@ -732,6 +732,41 @@ static bool nbcon_context_can_proceed(st return false; } +/** + * nbcon_can_proceed - Check whether ownership can proceed + * @wctxt: The write context that was handed to the write function + * + * Return: True if this context still owns the console. False if + * ownership was handed over or taken. + * + * It is used in nbcon_enter_unsafe() to make sure that it still owns the + * lock. Also it is used in nbcon_exit_unsafe() to eventually free the lock + * for a higher priority context which asked for the friendly handover. + * + * It can be called inside an unsafe section when the console is just + * temporary in safe state instead of exiting and entering the unsafe state. + * + * Also it can be called in the safe context before doing an expensive safe + * operation. It does not make sense to do the operation when a higher + * priority context took the lock. + * + * When this function returns false then the calling context no longer owns + * the console and is no longer allowed to go forward. In this case it must + * back out immediately and carefully. The buffer content is also no longer + * trusted since it no longer belongs to the calling context. + */ +bool nbcon_can_proceed(struct nbcon_write_context *wctxt) +{ + struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt); + struct console *con = ctxt->console; + struct nbcon_state cur; + + nbcon_state_read(con, &cur); + + return nbcon_context_can_proceed(ctxt, &cur); +} +EXPORT_SYMBOL_GPL(nbcon_can_proceed); + #define nbcon_context_enter_unsafe(c) __nbcon_context_update_unsafe(c, true) #define nbcon_context_exit_unsafe(c) __nbcon_context_update_unsafe(c, false) @@ -783,6 +818,46 @@ static bool __nbcon_context_update_unsaf } /** + * nbcon_enter_unsafe - Enter an unsafe region in the driver + * @wctxt: The write context that was handed to the write function + * + * Return: True if this context still owns the console. False if + * ownership was handed over or taken. + * + * When this function returns false then the calling context no longer owns + * the console and is no longer allowed to go forward. In this case it must + * back out immediately and carefully. The buffer content is also no longer + * trusted since it no longer belongs to the calling context. + */ +bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt) +{ + struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt); + + return nbcon_context_enter_unsafe(ctxt); +} +EXPORT_SYMBOL_GPL(nbcon_enter_unsafe); + +/** + * nbcon_exit_unsafe - Exit an unsafe region in the driver + * @wctxt: The write context that was handed to the write function + * + * Return: True if this context still owns the console. False if + * ownership was handed over or taken. + * + * When this function returns false then the calling context no longer owns + * the console and is no longer allowed to go forward. In this case it must + * back out immediately and carefully. The buffer content is also no longer + * trusted since it no longer belongs to the calling context. + */ +bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt) +{ + struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt); + + return nbcon_context_exit_unsafe(ctxt); +} +EXPORT_SYMBOL_GPL(nbcon_exit_unsafe); + +/** * nbcon_emit_next_record - Emit a record in the acquired context * @wctxt: The write context that will be handed to the write function *