From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Jan Kara <jack@suse.cz>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
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@linaro.org,
alex.elder@linaro.org, johan@kernel.org,
akpm@linux-foundation.org, rostedt@goodmis.org,
linux-pm@vger.kernel.org, Petr Mladek <pmladek@suse.com>
Subject: Re: [Query] Preemption (hogging) of the work handler
Date: Thu, 14 Jul 2016 09:55:24 +0900 [thread overview]
Message-ID: <20160714005524.GA517@swordfish> (raw)
In-Reply-To: <20160713153910.GY4695@ubuntu>
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?
part of suspend/hibernation is cpu_down(), which lands in console_cpu_notify(),
that does synchronous printing for every CPU taken down:
static int console_cpu_notify(struct notifier_block *self,
unsigned long action, void *hcpu)
{
switch (action) {
case CPU_ONLINE:
case CPU_DEAD:
case CPU_DOWN_FAILED:
case CPU_UP_CANCELED:
console_lock();
console_unlock();
^^^^^^^^^^^^^^
}
return NOTIFY_OK;
}
console_unlock() is synchronous (I posted a very early draft patch that makes
it asynchronous, but that's a future work). so if there is a ton of printk()-s,
then console_unlock() will print it, 100% guaranteed. even if printk_kthread
is doing the printing job at the moment, cpu down path will wait for it to
stop, lock the console semaphore, and got to console_unlock() printing loop.
in printk that you have posted, that will happen not only for CPU_DEAD,
but for CPU_DYING as well (possibly, there is a /* invoked with preemption
disabled, so defer */ comment, so may be you never endup doing direct
printk there, but then you schedule a console_unlock() work).
> That is why my Hacky patch tried to do it after devices are removed
> and irqs are disabled, but before syscore users are suspended (and
> timekeeping is one of them). And so it fixes it for me completely.
>
> IOW, we should switch back to synchronous printing after disabling
> interrupts on the last running CPU.
>
> And I of course agree with Rafael that we would need something similar
> in Hibernation code path as well, if we choose to fix it my way.
suspend/hibernation/kexec - all covered by this patch.
-ss
next prev parent reply other threads:[~2016-07-14 0:55 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-01 16:59 [Query] Preemption (hogging) of the work handler Viresh Kumar
2016-07-01 17:22 ` Tejun Heo
2016-07-01 17:28 ` Viresh Kumar
2016-07-06 18:28 ` Viresh Kumar
2016-07-06 19:23 ` Steven Rostedt
2016-07-06 19:25 ` Viresh Kumar
2016-07-11 10:26 ` Jan Kara
2016-07-11 15:44 ` Sergey Senozhatsky
2016-07-11 22:35 ` Viresh Kumar
2016-07-11 22:44 ` Rafael J. Wysocki
2016-07-11 22:46 ` Viresh Kumar
2016-07-12 12:24 ` Rafael J. Wysocki
2016-07-12 13:02 ` Viresh Kumar
2016-07-12 13:56 ` Petr Mladek
2016-07-12 14:04 ` Viresh Kumar
2016-07-12 9:38 ` Sergey Senozhatsky
2016-07-12 12:52 ` Petr Mladek
2016-07-12 13:12 ` Viresh Kumar
2016-07-12 17:11 ` Viresh Kumar
2016-07-12 19:59 ` Rafael J. Wysocki
2016-07-12 20:08 ` Viresh Kumar
2016-07-13 7:00 ` Sergey Senozhatsky
2016-07-13 12:05 ` Rafael J. Wysocki
2016-07-13 12:57 ` Sergey Senozhatsky
2016-07-13 13:22 ` Rafael J. Wysocki
2016-07-12 14:03 ` Sergey Senozhatsky
2016-07-12 14:12 ` Viresh Kumar
2016-07-14 23:52 ` Viresh Kumar
2016-07-15 13:11 ` Sergey Senozhatsky
2016-07-15 15:57 ` Viresh Kumar
2016-07-12 23:19 ` Viresh Kumar
2016-07-13 0:18 ` Viresh Kumar
2016-07-13 5:45 ` Sergey Senozhatsky
2016-07-13 15:39 ` Viresh Kumar
2016-07-13 23:08 ` Rafael J. Wysocki
2016-07-13 23:18 ` Viresh Kumar
2016-07-13 23:38 ` Greg Kroah-Hartman
2016-07-14 0:55 ` Sergey Senozhatsky [this message]
2016-07-14 1:09 ` Rafael J. Wysocki
2016-07-14 1:32 ` Sergey Senozhatsky
2016-07-14 21:57 ` Viresh Kumar
2016-07-14 21:55 ` Viresh Kumar
2016-07-14 14:12 ` Jan Kara
2016-07-14 14:33 ` Rafael J. Wysocki
2016-07-14 14:39 ` Jan Kara
2016-07-14 14:47 ` Rafael J. Wysocki
2016-07-14 14:55 ` Jan Kara
2016-07-14 22:14 ` Viresh Kumar
2016-07-14 14:34 ` Sergey Senozhatsky
2016-07-14 15:03 ` Jan Kara
2016-07-14 22:12 ` Viresh Kumar
2016-07-18 11:01 ` Jan Kara
2016-07-18 11:49 ` Rafael J. Wysocki
2016-07-29 20:42 ` Viresh Kumar
2016-07-30 2:12 ` Sergey Senozhatsky
2016-07-11 19:03 ` Viresh Kumar
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