linux-kernel - Re: lockdep splat during suspend

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Date:   Thu, 17 Nov 2016 17:31:55 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
cc:     Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: lockdep splat during suspend

On Thu, 17 Nov 2016, Sebastian Andrzej Siewior wrote:

> On 2016-11-17 13:43:58 [+0100], Borislav Petkov wrote:
> > Hi dudes,
> Hi Boris,
> 
> > this is what I'm seeing on 4.9-rc5+tip/master during suspend. (And yes,
> > that printk thing is nuts):
> 
> assuming this happens always, could you please try to revert
>   90b14889d2f9 ("kernel/printk: Convert to hotplug state machine")
> and see if it still there? I am curious if this is new or old splat.

It's a new one and that patch simply missed the fact, that the actions in
the original notifier were all w/o FROZEN, but the conversion dropped
that. Which probably explains the splat because suspend/resume is where the
FROZEN stuff happens.

Boris, does the patch below fix the issue for you ?

Thanks,

	tglx

8<-----------------------

--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2194,8 +2194,10 @@ void resume_console(void)
  */
 static int console_cpu_notify(unsigned int cpu)
 {
-	console_lock();
-	console_unlock();
+	if (!cpuhp_tasks_frozen) {
+		console_lock();
+		console_unlock();
+	}
 	return 0;
 }