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printk: Add is_printk_legacy_deferred()

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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 <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20240820063001.36405-24-john.ogness@linutronix.de
Signed-off-by: Petr Mladek <pmladek@suse.com>
This commit is contained in:
John Ogness 2024-08-20 08:35:49 +02:06 committed by Petr Mladek
parent c158834b22
commit 70411bf8d2
2 changed files with 12 additions and 1 deletions
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2
kernel/printk/internal.h
View File

@ -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(struct console *con, short flags)
#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; }

11
kernel/printk/printk_safe.c
View File

@ -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, va_list args)
* 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. */