panic: Mark emergency section in oops

Mark an emergency section beginning with oops_enter() until the
end of oops_exit(). In this section, every printk() call will
attempt to directly flush to the consoles using the EMERGENCY
priority.

The very end of oops_exit() performs a kmsg_dump(). This is not
included in the emergency section because it is another
flushing mechanism that should occur after the consoles have
flushed the oops messages.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20240820063001.36405-34-john.ogness@linutronix.deSigned-off-by: Petr Mladek <pmladek@suse.com>

kernel/panic.c

@@ -685,6 +685,7 @@ bool oops_may_print(void)
  */
 void oops_enter(void)
 {
+	nbcon_cpu_emergency_enter();
 	tracing_off();
 	/* can't trust the integrity of the kernel anymore: */
 	debug_locks_off();
@@ -707,6 +708,7 @@ void oops_exit(void)
 {
 	do_oops_enter_exit();
 	print_oops_end_marker();
+	nbcon_cpu_emergency_exit();
 	kmsg_dump(KMSG_DUMP_OOPS);
 }