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printk: Add function to replay kernel log on consoles

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Add a generic function console_replay_all() for replaying
the kernel log on consoles, in any context. It would allow
viewing the logs on an unresponsive terminal via sysrq.

Reuse the existing code from console_flush_on_panic() for
resetting the sequence numbers, by introducing a new helper
function __console_rewind_all(). It is safe to be called
under console_lock().

Try to acquire lock on the console subsystem without waiting.
If successful, reset the sequence number to oldest available
record on all consoles and call console_unlock() which will
automatically flush the messages to the consoles.

Suggested-by: John Ogness <john.ogness@linutronix.de>
Suggested-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Shimoyashiki Taichi <taichi.shimoyashiki@sony.com>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sreenath Vijayan <sreenath.vijayan@sony.com>
Link: https://lore.kernel.org/r/90ee131c643a5033d117b556c0792de65129d4c3.1710220326.git.sreenath.vijayan@sony.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Sreenath Vijayan 2024-03-13 15:50:52 +05:30 committed by Greg Kroah-Hartman
parent 25ca2d573e
commit 693f75b91a
2 changed files with 57 additions and 24 deletions
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4
include/linux/printk.h
View file

@ -195,6 +195,7 @@ void show_regs_print_info(const char *log_lvl);
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_replay_all(void);
#else
static inline __printf(1, 0)
int vprintk(const char *s, va_list args)
@ -274,6 +275,9 @@ static inline void dump_stack(void)
static inline void printk_trigger_flush(void)
{
}
static inline void console_replay_all(void)
{
}
#endif
bool this_cpu_in_panic(void);

77
kernel/printk/printk.c
View file

@ -3161,6 +3161,40 @@ void console_unblank(void)
pr_flush(1000, true);
}
/*
* Rewind all consoles to the oldest available record.
*
* IMPORTANT: The function is safe only when called under
* console_lock(). It is not enforced because
* it is used as a best effort in panic().
*/
static void __console_rewind_all(void)
{
struct console *c;
short flags;
int cookie;
u64 seq;
seq = prb_first_valid_seq(prb);
cookie = console_srcu_read_lock();
for_each_console_srcu(c) {
flags = console_srcu_read_flags(c);
if (flags & CON_NBCON) {
nbcon_seq_force(c, seq);
} else {
/*
* This assignment is safe only when called under
* console_lock(). On panic, legacy consoles are
* only best effort.
*/
c->seq = seq;
}
}
console_srcu_read_unlock(cookie);
}
/**
* console_flush_on_panic - flush console content on panic
* @mode: flush all messages in buffer or just the pending ones
@ -3189,30 +3223,8 @@ void console_flush_on_panic(enum con_flush_mode mode)
*/
console_may_schedule = 0;
if (mode == CONSOLE_REPLAY_ALL) {
struct console *c;
short flags;
int cookie;
u64 seq;
seq = prb_first_valid_seq(prb);
cookie = console_srcu_read_lock();
for_each_console_srcu(c) {
flags = console_srcu_read_flags(c);
if (flags & CON_NBCON) {
nbcon_seq_force(c, seq);
} else {
/*
* This is an unsynchronized assignment. On
* panic legacy consoles are only best effort.
*/
c->seq = seq;
}
}
console_srcu_read_unlock(cookie);
}
if (mode == CONSOLE_REPLAY_ALL)
__console_rewind_all();
console_flush_all(false, &next_seq, &handover);
}
@ -4301,6 +4313,23 @@ void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
}
EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
/**
* console_replay_all - replay kernel log on consoles
*
* Try to obtain lock on console subsystem and replay all
* available records in printk buffer on the consoles.
* Does nothing if lock is not obtained.
*
* Context: Any context.
*/
void console_replay_all(void)
{
if (console_trylock()) {
__console_rewind_all();
/* Consoles are flushed as part of console_unlock(). */
console_unlock();
}
}
#endif
#ifdef CONFIG_SMP