Printk changes for 4.21

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Merge tag 'printk-for-4.21' of git://git.kernel.org/pub/scm/linux/kernel/git/pmladek/printk

Pull printk updates from Petr Mladek:

 - Keep spinlocks busted until the end of panic()

 - Fix races between calculating number of messages that would fit into
   user space buffers, filling the buffers, and switching printk.time
   parameter

 - Some code clean up

* tag 'printk-for-4.21' of git://git.kernel.org/pub/scm/linux/kernel/git/pmladek/printk:
  printk: Remove print_prefix() calls with NULL buffer.
  printk: fix printk_time race.
  printk: Make printk_emit() local function.
  panic: avoid deadlocks in re-entrant console drivers

kernel/panic.c

@@ -14,6 +14,7 @@
 #include <linux/kmsg_dump.h>
 #include <linux/kallsyms.h>
 #include <linux/notifier.h>
+#include <linux/vt_kern.h>
 #include <linux/module.h>
 #include <linux/random.h>
 #include <linux/ftrace.h>
@@ -237,7 +238,10 @@ void panic(const char *fmt, ...)
 	if (_crash_kexec_post_notifiers)
 		__crash_kexec(NULL);
 
-	bust_spinlocks(0);
+#ifdef CONFIG_VT
+	unblank_screen();
+#endif
+	console_unblank();
 
 	/*
 	 * We may have ended up stopping the CPU holding the lock (in