Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage

[Sergey Senozhatsky]

Hello,

On (04/06/17 19:33), Pavel Machek wrote:
> > This patch set gives up part of the printk() reliability for bounded
> > latency (at least unless we detect we are really in trouble) which is IMHO
> > a good trade-off for lots of users (and others can just turn this feature
> > off).
> 
> If they can ever realize they were bitten by this feature.
> 
> Can we go for different tradeoff?
> 
> In console_unlock(), if you detect too much work, print "Too many
> messages to print, %d bytes delayed" and wake up kernel thread.

"too many messages" is undefined. console_unlock() can be called from
IRQ handler or with preemtion disabled, or under spin_lock, or under
RCU read lock, etc. etc. By the time we decide to wake up printk_kthread
from console_unlock() it may be already too late.

besides, this does not really address any of the concerns you have
pointed out in other emails. we might be unable to wake_up printk_kthread
(because there is a misbehaving higher prio process, or because the
scheduler is misbehaving, etc. etc.) so the "emergency mode" is still
here and still requires special handling.

	-ss