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printk: Wait for the global console lock when the system is going down

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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
This commit is contained in:
Petr Mladek 2022-06-15 18:28:05 +02:00
parent c3230283e2
commit b87f02307d
6 changed files with 47 additions and 0 deletions
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5
include/linux/printk.h
View file

@ -174,6 +174,7 @@ extern void printk_prefer_direct_enter(void);
extern void printk_prefer_direct_exit(void);
extern bool pr_flush(int timeout_ms, bool reset_on_progress);
extern void try_block_console_kthreads(int timeout_ms);
/*
* Please don't use printk_ratelimit(), because it shares ratelimiting state
@ -238,6 +239,10 @@ static inline bool pr_flush(int timeout_ms, bool reset_on_progress)
return true;
}
static inline void try_block_console_kthreads(int timeout_ms)
{
}
static inline int printk_ratelimit(void)
{
return 0;