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Date: Thu, 13 Apr 2017 14:50:47 +0900
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Petr Mladek <pmladek@suse.com>, Pavel Machek <pavel@ucw.cz>
Cc: Jan Kara <jack@suse.cz>, "Eric W. Biederman" <ebiederm@xmission.com>,
        Ye Xiaolong <xiaolong.ye@intel.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        "Rafael J . Wysocki" <rjw@rjwysocki.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jslaby@suse.com>, Len Brown <len.brown@intel.com>,
        linux-kernel@vger.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Subject: Re: [printk]  fbc14616f4:
 BUG:kernel_reboot-without-warning_in_test_stage
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On (04/12/17 01:19), Sergey Senozhatsky wrote:
[..]
> it does offloading after X printed lines by the same process.
> if we reschedule, then the counter resets. which is probably OK,
> we don't really want any process, except for printk_kthread, to
> stay in console_unlock() forever.

may be this can be changed. we don't want even printk_kthread to keep
console_sem locked for too long, because other process that might want
to lock console_sem have to sleep in TASK_UNINTERRUPTIBLE as long as
printing thread has pending messages to print. so may be the rule can
be "every process prints up to `atomic_print_limit' lines and then
offloads printing - wake_up()s printk_kthread and up()s console_sem".
some other process (printk_kthread or a process from console_sem wait
list, let them compete for console_sem) will eventually down()
console_sem and print the next `atomic_print_limit' lines, while
current process will have a chance to return from console_unlock() and
do something else.

[..]
> the next question will be -- do we even need printk_emergency_begin/end
> or we can leave without it.

what I meant here -- drop sysrq and kexec printk_emergency_begin/end
patches, but keep printk_emergency_begin/end API and do
printk_emergency_begin/end in console_suspend()/resume().
PM already calls console_suspend()/resume(). something like that...

	-ss