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