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From: "Rafael J. Wysocki" <rafael@kernel.org>
Date: Thu, 14 Jul 2016 03:09:01 +0200
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Subject: Re: [Query] Preemption (hogging) of the work handler
To: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Viresh Kumar <viresh.kumar@linaro.org>, Jan Kara <jack@suse.cz>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>, Tejun Heo <tj@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        vlevenetz@mm-sol.com, Vaibhav Hiremath <vaibhav.hiremath@linaro.org>,
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        Andrew Morton <akpm@linux-foundation.org>,
        Steven Rostedt <rostedt@goodmis.org>,
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On Thu, Jul 14, 2016 at 2:55 AM, Sergey Senozhatsky
<sergey.senozhatsky.work@gmail.com> wrote:
> Hello,
>
> On (07/13/16 08:39), Viresh Kumar wrote:
> [..]
>> Maybe not, as this can still lead to the original bug we were all
>> chasing. This may hog some other CPU if we are doing excessive
>> printing in suspend :(
>
> excessive printing is just part of the problem here. if we cab cond_resched()
> in console_unlock() (IOW, we execute console_unlock() with preemption and
> interrupts enabled) then everything must be ok, and *from printing POV* there
> is no difference whether it's printk_kthread or anything else in this case.
> the difference jumps in when original console_unlock() is executed with
> preemption/irq disabled, then offloading it to schedulable printk_kthread is
> the right thing.
>
>> suspend_console() is called quite early, so for example in my case we
>> do lots of printing during suspend (not from the suspend thread, but
>> an IRQ handled by the USB subsystem, which removes a bus with help of
>> some other thread probably).
>
> a silly question -- can we suspend consoles later?

Not really and I'm not sure how that would help?