printk: Wait for the global console lock when the system is going down
authorPetr Mladek <pmladek@suse.com>
Wed, 15 Jun 2022 16:28:05 +0000 (18:28 +0200)
committerPetr Mladek <pmladek@suse.com>
Wed, 15 Jun 2022 20:04:15 +0000 (22:04 +0200)
commitb87f02307d3cfbda768520f0687c51ca77e14fc3
treeb95087d60c973b8fa365b0a2ab1a49c3e8373451
parentc3230283e2819a69dad2cf7a63143fde8bab8b5c
printk: Wait for the global console lock when the system is going down

There are reports that the console kthreads block the global console
lock when the system is going down, for example, reboot, panic.

First part of the solution was to block kthreads in these problematic
system states so they stopped handling newly added messages.

Second part of the solution is to wait when for the kthreads when
they are actively printing. It solves the problem when a message
was printed before the system entered the problematic state and
the kthreads managed to step in.

A busy waiting has to be used because panic() can be called in any
context and in an unknown state of the scheduler.

There must be a timeout because the kthread might get stuck or sleeping
and never release the lock. The timeout 10s is an arbitrary value
inspired by the softlockup timeout.

Link: https://lore.kernel.org/r/20220610205038.GA3050413@paulmck-ThinkPad-P17-Gen-1
Link: https://lore.kernel.org/r/CAMdYzYpF4FNTBPZsEFeWRuEwSies36QM_As8osPWZSr2q-viEA@mail.gmail.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/r/20220615162805.27962-3-pmladek@suse.com
include/linux/printk.h
kernel/panic.c
kernel/printk/internal.h
kernel/printk/printk.c
kernel/printk/printk_safe.c
kernel/reboot.c