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Date: Tue, 6 Sep 2016 16:16:27 +0900
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Jan Kara <jack@suse.cz>, Viresh Kumar <viresh.kumar@linaro.org>,
        Andrew Morton <akpm@linux-foundation.org>, Jan Kara <jack@suse.com>,
        Tejun Heo <tj@kernel.org>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Byungchul Park <byungchul.park@lge.com>, vlevenetz@mm-sol.com,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH v10 1/2] printk: Make printk() completely async
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Hello,

On (09/02/16 17:15), Petr Mladek wrote:
[..]
> > I meant that this thing
> > 
> > 	local_irq_save() // or preempt_disable()
> > 	...
> > 	if (console_trylock())
> > 		console_unlock();
> > 	...
> > 	local_irq_restore() // or preempt_enable()
> 
> I see.
> 
> > can easily lockup the system if console_trylock() was successful and there
> > are enough messages to print. printk_kthread can't help, because here we
> > basically enforce the `old' behavior. we have async printk, but not async
> > console output. tweaking console_unlock() to offload the actual printing loop
> > to printk_kthread would make the entire console output async:
> > 
> > 	static void console_sync_flush_and_unlock(void)
> > 	{
> > 		for (;;) {
> > 		...
> > 			call_console_drivers();
> > 		...
> > 		}
> > 	}
> > 
> > 	void console_unlock(void)
> > 	{
> > 		if (!MOTORMOUTH && can_printk_async()) {
> > 			up();
> > 			wake_up_process(printk_kthread);
> > 			return;
> > 		}
> > 		console_sync_flush_and_unlock();
> > 	}
> 
> Something like this would make sense. But I would do it in a separate
> patch(set). We need to go through all console_unlock() callers and
> make sure that they are fine with the potential async behavior.
> I would not complicate the async printk patchset by this.

sure. just added one more item to the list.

	-ss