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nbcon: Add API to acquire context for non-printing operations

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Provide functions nbcon_device_try_acquire() and
nbcon_device_release() which will try to acquire the nbcon
console ownership with NBCON_PRIO_NORMAL and mark it unsafe for
handover/takeover.

These functions are to be used together with the device-specific
locking when performing non-printing activities on the console
device. They will allow synchronization against the
atomic_write() callback which will be serialized, for higher
priority contexts, only by acquiring the console context
ownership.

Pitfalls:

The API requires to be called in a context with migration
disabled because it uses per-CPU variables internally.

The context is set unsafe for a takeover all the time. It
guarantees full serialization against any atomic_write() caller
except for the final flush in panic() which might try an unsafe
takeover.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20240820063001.36405-14-john.ogness@linutronix.de
Signed-off-by: Petr Mladek <pmladek@suse.com>
This commit is contained in:
John Ogness
2024-08-20 08:35:39 +02:06
committed by Petr Mladek
parent dc219d8d85
commit adf6f37d14
3 changed files with 73 additions and 1 deletions
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include/linux/printk.h
+14
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@@ -9,6 +9,8 @@
#include <linux/ratelimit_types.h>
#include <linux/once_lite.h>
struct console;
extern const char linux_banner[];
extern const char linux_proc_banner[];
@@ -198,6 +200,8 @@ extern asmlinkage void dump_stack_lvl(const char *log_lvl) __cold;
extern asmlinkage void dump_stack(void) __cold;
void printk_trigger_flush(void);
void console_try_replay_all(void);
extern bool nbcon_device_try_acquire(struct console *con);
extern void nbcon_device_release(struct console *con);
#else
static inline __printf(1, 0)
int vprintk(const char *s, va_list args)
@@ -280,6 +284,16 @@ static inline void printk_trigger_flush(void)
static inline void console_try_replay_all(void)
{
}
static inline bool nbcon_device_try_acquire(struct console *con)
{
return false;
}
static inline void nbcon_device_release(struct console *con)
{
}
#endif
bool this_cpu_in_panic(void);