From: John Ogness Date: Tue, 20 Aug 2024 08:35:49 +0206 Subject: [PATCH 23/54] printk: Add is_printk_legacy_deferred() Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.11/older/patches-6.11-rt7.tar.xz If printk has been explicitly deferred or is called from NMI context, legacy console printing must be deferred to an irq_work context. Introduce a helper function is_printk_legacy_deferred() for a CPU to query if it must defer legacy console printing. In follow-up commits this helper will be needed at other call sites as well. Signed-off-by: John Ogness Reviewed-by: Petr Mladek Link: https://lore.kernel.org/r/20240820063001.36405-24-john.ogness@linutronix.de Signed-off-by: Petr Mladek Signed-off-by: Sebastian Andrzej Siewior --- kernel/printk/internal.h | 2 ++ kernel/printk/printk_safe.c | 11 ++++++++++- 2 files changed, 12 insertions(+), 1 deletion(-) --- a/kernel/printk/internal.h +++ b/kernel/printk/internal.h @@ -75,6 +75,7 @@ bool printk_percpu_data_ready(void); } while (0) void defer_console_output(void); +bool is_printk_legacy_deferred(void); u16 printk_parse_prefix(const char *text, int *level, enum printk_info_flags *flags); @@ -138,6 +139,7 @@ static inline bool console_is_usable(str #define printk_safe_exit_irqrestore(flags) local_irq_restore(flags) static inline bool printk_percpu_data_ready(void) { return false; } +static inline bool is_printk_legacy_deferred(void) { return false; } static inline u64 nbcon_seq_read(struct console *con) { return 0; } static inline void nbcon_seq_force(struct console *con, u64 seq) { } static inline bool nbcon_alloc(struct console *con) { return false; } --- a/kernel/printk/printk_safe.c +++ b/kernel/printk/printk_safe.c @@ -38,6 +38,15 @@ void __printk_deferred_exit(void) __printk_safe_exit(); } +bool is_printk_legacy_deferred(void) +{ + /* + * The per-CPU variable @printk_context can be read safely in any + * context. CPU migration is always disabled when set. + */ + return (this_cpu_read(printk_context) || in_nmi()); +} + asmlinkage int vprintk(const char *fmt, va_list args) { #ifdef CONFIG_KGDB_KDB @@ -50,7 +59,7 @@ asmlinkage int vprintk(const char *fmt, * Use the main logbuf even in NMI. But avoid calling console * drivers that might have their own locks. */ - if (this_cpu_read(printk_context) || in_nmi()) + if (is_printk_legacy_deferred()) return vprintk_deferred(fmt, args); /* No obstacles. */