From ed76c07c6885b249ce8486dac22fb97151a83185 Mon Sep 17 00:00:00 2001 From: Marcos Paulo de Souza Date: Tue, 5 Nov 2024 16:45:08 -0300 Subject: [PATCH 1/3] printk: Introduce FORCE_CON flag Introduce FORCE_CON flag to printk. The new flag will make it possible to create a context where printk messages will never be suppressed. This mechanism will be used in the next patch to create a force_con context on sysrq handling, removing an existing workaround on the loglevel global variable. The workaround existed to make sure that sysrq header messages were sent to all consoles, but this doesn't work with deferred messages because the loglevel might be restored to its original value before a console flushes the messages. Signed-off-by: Marcos Paulo de Souza Reviewed-by: John Ogness Reviewed-by: Petr Mladek Acked-by: Greg Kroah-Hartman Link: https://lore.kernel.org/r/20241105-printk-loud-con-v2-1-bd3ecdf7b0e4@suse.com Signed-off-by: Petr Mladek --- include/linux/printk.h | 3 +++ kernel/printk/internal.h | 3 +++ kernel/printk/printk.c | 21 ++++++++++++++++----- kernel/printk/printk_safe.c | 18 ++++++++++++++++++ 4 files changed, 40 insertions(+), 5 deletions(-) diff --git a/include/linux/printk.h b/include/linux/printk.h index eca9bb2ee637b6..232e5fd0670188 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -166,6 +166,9 @@ __printf(1, 2) __cold int _printk_deferred(const char *fmt, ...); extern void __printk_deferred_enter(void); extern void __printk_deferred_exit(void); +extern void printk_force_console_enter(void); +extern void printk_force_console_exit(void); + /* * The printk_deferred_enter/exit macros are available only as a hack for * some code paths that need to defer all printk console printing. Interrupts diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h index 3fcb48502adbd8..c6bb47666aef67 100644 --- a/kernel/printk/internal.h +++ b/kernel/printk/internal.h @@ -53,6 +53,8 @@ int devkmsg_sysctl_set_loglvl(const struct ctl_table *table, int write, /* Flags for a single printk record. */ enum printk_info_flags { + /* always show on console, ignore console_loglevel */ + LOG_FORCE_CON = 1, LOG_NEWLINE = 2, /* text ended with a newline */ LOG_CONT = 8, /* text is a fragment of a continuation line */ }; @@ -90,6 +92,7 @@ bool printk_percpu_data_ready(void); void defer_console_output(void); bool is_printk_legacy_deferred(void); +bool is_printk_force_console(void); u16 printk_parse_prefix(const char *text, int *level, enum printk_info_flags *flags); diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 71e4fe6f9b85ed..7cb44f9f382533 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -1319,11 +1319,11 @@ static void boot_delay_msec(int level) { unsigned long long k; unsigned long timeout; + bool suppress = !is_printk_force_console() && + suppress_message_printing(level); - if ((boot_delay == 0 || system_state >= SYSTEM_RUNNING) - || suppress_message_printing(level)) { + if ((boot_delay == 0 || system_state >= SYSTEM_RUNNING) || suppress) return; - } k = (unsigned long long)loops_per_msec * boot_delay; @@ -2273,6 +2273,9 @@ int vprintk_store(int facility, int level, if (dev_info) flags |= LOG_NEWLINE; + if (is_printk_force_console()) + flags |= LOG_FORCE_CON; + if (flags & LOG_CONT) { prb_rec_init_wr(&r, reserve_size); if (prb_reserve_in_last(&e, prb, &r, caller_id, PRINTKRB_RECORD_MAX)) { @@ -2280,6 +2283,9 @@ int vprintk_store(int facility, int level, facility, &flags, fmt, args); r.info->text_len += text_len; + if (flags & LOG_FORCE_CON) + r.info->flags |= LOG_FORCE_CON; + if (flags & LOG_NEWLINE) { r.info->flags |= LOG_NEWLINE; prb_final_commit(&e); @@ -2947,6 +2953,7 @@ bool printk_get_next_message(struct printk_message *pmsg, u64 seq, struct printk_info info; struct printk_record r; size_t len = 0; + bool force_con; /* * Formatting extended messages requires a separate buffer, so use the @@ -2965,9 +2972,13 @@ bool printk_get_next_message(struct printk_message *pmsg, u64 seq, pmsg->seq = r.info->seq; pmsg->dropped = r.info->seq - seq; + force_con = r.info->flags & LOG_FORCE_CON; - /* Skip record that has level above the console loglevel. */ - if (may_suppress && suppress_message_printing(r.info->level)) + /* + * Skip records that are not forced to be printed on consoles and that + * has level above the console loglevel. + */ + if (!force_con && may_suppress && suppress_message_printing(r.info->level)) goto out; if (is_extended) { diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c index 2b35a9d3919d8b..6f94418d53ffba 100644 --- a/kernel/printk/printk_safe.c +++ b/kernel/printk/printk_safe.c @@ -12,6 +12,24 @@ #include "internal.h" +/* Context where printk messages are never suppressed */ +static atomic_t force_con; + +void printk_force_console_enter(void) +{ + atomic_inc(&force_con); +} + +void printk_force_console_exit(void) +{ + atomic_dec(&force_con); +} + +bool is_printk_force_console(void) +{ + return atomic_read(&force_con); +} + static DEFINE_PER_CPU(int, printk_context); /* Can be preempted by NMI. */ From e3eea25e0b28ea06eb841ef1814ce7b7254f2fce Mon Sep 17 00:00:00 2001 From: Marcos Paulo de Souza Date: Tue, 5 Nov 2024 16:45:09 -0300 Subject: [PATCH 2/3] tty: sysrq: Use printk_force_console context on __handle_sysrq By using the printk_force_console the loglevel workaround can be removed. The workaround existed to always send the sysrq header message to all consoles not matter what was the current loglevel, but it won't work for deferred messages, since the loglevel can be restore before the message is printed, suppressing the message that wasn't supposed to be suppressed by the workaround. Signed-off-by: Marcos Paulo de Souza Reviewed-by: John Ogness Reviewed-by: Petr Mladek Acked-by: Greg Kroah-Hartman Link: https://lore.kernel.org/r/20241105-printk-loud-con-v2-2-bd3ecdf7b0e4@suse.com Signed-off-by: Petr Mladek --- drivers/tty/sysrq.c | 18 ++++++++---------- 1 file changed, 8 insertions(+), 10 deletions(-) diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c index 14f8f00fdcf9ab..4a8405478ad812 100644 --- a/drivers/tty/sysrq.c +++ b/drivers/tty/sysrq.c @@ -582,7 +582,6 @@ static void __sysrq_put_key_op(u8 key, const struct sysrq_key_op *op_p) void __handle_sysrq(u8 key, bool check_mask) { const struct sysrq_key_op *op_p; - int orig_log_level; int orig_suppress_printk; int i; @@ -592,13 +591,12 @@ void __handle_sysrq(u8 key, bool check_mask) rcu_sysrq_start(); rcu_read_lock(); /* - * Raise the apparent loglevel to maximum so that the sysrq header - * is shown to provide the user with positive feedback. We do not - * simply emit this at KERN_EMERG as that would change message - * routing in the consumers of /proc/kmsg. + * Enter in the force_console context so that sysrq header is shown to + * provide the user with positive feedback. We do not simply emit this + * at KERN_EMERG as that would change message routing in the consumers + * of /proc/kmsg. */ - orig_log_level = console_loglevel; - console_loglevel = CONSOLE_LOGLEVEL_DEFAULT; + printk_force_console_enter(); op_p = __sysrq_get_key_op(key); if (op_p) { @@ -608,11 +606,11 @@ void __handle_sysrq(u8 key, bool check_mask) */ if (!check_mask || sysrq_on_mask(op_p->enable_mask)) { pr_info("%s\n", op_p->action_msg); - console_loglevel = orig_log_level; + printk_force_console_exit(); op_p->handler(key); } else { pr_info("This sysrq operation is disabled.\n"); - console_loglevel = orig_log_level; + printk_force_console_exit(); } } else { pr_info("HELP : "); @@ -630,7 +628,7 @@ void __handle_sysrq(u8 key, bool check_mask) } } pr_cont("\n"); - console_loglevel = orig_log_level; + printk_force_console_exit(); } rcu_read_unlock(); rcu_sysrq_end(); From da115c4ee29f589bb72ec2e86eb5e196b6bbcb41 Mon Sep 17 00:00:00 2001 From: Arnd Bergmann Date: Tue, 12 Nov 2024 15:29:15 +0100 Subject: [PATCH 3/3] printk: add dummy printk_force_console_enter/exit helpers The newly added interface is broken when PRINTK is disabled: drivers/tty/sysrq.c: In function '__handle_sysrq': drivers/tty/sysrq.c:601:9: error: implicit declaration of function 'printk_force_console_enter' [-Wimplicit-function-declaration] 601 | printk_force_console_enter(); | ^~~~~~~~~~~~~~~~~~~~~~~~~~ drivers/tty/sysrq.c:611:25: error: implicit declaration of function 'printk_force_console_exit' [-Wimplicit-function-declaration] 611 | printk_force_console_exit(); | ^~~~~~~~~~~~~~~~~~~~~~~~~ Add empty stub functions for both. Fixes: ed76c07c6885 ("printk: Introduce FORCE_CON flag") Signed-off-by: Arnd Bergmann Reviewed-by: Andy Shevchenko Reviewed-by: Marcos Paulo de Souza Tested-by: Marcos Paulo de Souza Link: https://lore.kernel.org/r/20241112142939.724093-1-arnd@kernel.org Signed-off-by: Petr Mladek --- include/linux/printk.h | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/include/linux/printk.h b/include/linux/printk.h index 232e5fd0670188..4217a9f412b265 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -232,6 +232,14 @@ static inline void printk_deferred_exit(void) { } +static inline void printk_force_console_enter(void) +{ +} + +static inline void printk_force_console_exit(void) +{ +} + static inline int printk_ratelimit(void) { return 0;