From 6947abe17d30a4904d2c00d21647b10edd5d94a4 Mon Sep 17 00:00:00 2001 From: Zhang Enpei Date: Fri, 6 Jun 2025 19:46:39 +0800 Subject: [PATCH] printk: nbcon: Allow drivers to mark unsafe regions and check state commit 2f5d0c4c883ae3ccc57ab9991f6787a941e9f751 upstream. 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 +++++++++++++++++++++++++++++++++++++++++ xx.log | 20 +++++++++++ 3 files changed, 105 insertions(+) create mode 100644 xx.log diff --git a/include/linux/console.h b/include/linux/console.h index 20cd486b76ad..dbdbd943b895 100644 --- a/include/linux/console.h +++ b/include/linux/console.h @@ -430,6 +430,16 @@ static inline bool console_is_registered(const struct console *con) 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; diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c index e076096b31c0..e667f653cc56 100644 --- a/kernel/printk/nbcon.c +++ b/kernel/printk/nbcon.c @@ -733,6 +733,41 @@ static bool nbcon_context_can_proceed(struct nbcon_context *ctxt, struct nbcon_s 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) @@ -784,6 +819,46 @@ static bool __nbcon_context_update_unsafe(struct nbcon_context *ctxt, bool unsaf return nbcon_context_can_proceed(ctxt, &cur); } +/** + * 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_alloc - Allocate buffers needed by the nbcon console * @con: Console to allocate buffers for diff --git a/xx.log b/xx.log new file mode 100644 index 000000000000..be784808534d --- /dev/null +++ b/xx.log @@ -0,0 +1,20 @@ +printk: nbcon: Allow drivers to mark unsafe regions and check state + +commit 2f5d0c4c883ae3ccc57ab9991f6787a941e9f751 upstream. + +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 + -- Gitee