linux-kernel - Re: WARNING: CPU: 1 PID: 0 at kernel/time/tick-broadcast.c:668 tick_broadcast_oneshot

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Message-ID: <20140211082306.GA1528@redhat.com>
Date:	Tue, 11 Feb 2014 09:23:08 +0100
From:	Stanislaw Gruszka <sgruszka@...hat.com>
To:	poma <pomidorabelisima@...il.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	linux-pm@...r.kernel.org, Olaf Hering <olaf@...fle.de>,
	Dave Jones <davej@...hat.com>,
	"Justin M. Forbes" <jforbes@...hat.com>,
	Josh Boyer <jwboyer@...hat.com>,
	Mailing-List fedora-kernel <kernel@...ts.fedoraproject.org>
Subject: Re: WARNING: CPU: 1 PID: 0 at kernel/time/tick-broadcast.c:668
 tick_broadcast_oneshot_control+0x17d/0x190()

On Mon, Feb 10, 2014 at 07:59:39PM +0100, poma wrote:
> On 10.02.2014 11:06, Thomas Gleixner wrote:
> > On Mon, 10 Feb 2014, poma wrote:
> > 
> >> [   83.558551]  [<ffffffff81025b17>] amd_e400_idle+0x87/0x130
> > 
> > So this seems to happen only on AMD machines which use that e400 idle
> > mode. I have no idea at the moment whats wrong there. I'll find one of
> > those machines and try to reproduce.

I tried to debug that warn as well. Even if I found machine with proper
family and model number, HW C1E bug do not happen there, hence I just
hack kernel to always use amd_e400_idle (and remove AMD rdmsr specific
instructions to do not crash). That make issue 100% reproducible when
suspend/resume.

It happens when cpu become idle, call CLOCK_EVT_NOTIFY_BROADCAST_ENTER,
but before CLOCK_EVT_NOTIFY_BROADCAST_EXIT, interrupt trigger on that
cpu. IRQ is handled by hrtimer code, which want to switch to hres and
call:

tick_switch_to_oneshot() -> ... -> tick_broadcast_setup_oneshot()

Since we have already proper handler there, last procedure clear
tick_broadcast_oneshot_mask, but tick_broadcast_pending_mask stay
set. When amd_e400_idle next time call CLOCK_EVT_NOTIFY_BROADCAST_ENTER,
the warning will happen.

I came with a below patch, which also clear pending mask, but perhaps
oneshot_mask should not be cleared on tick_broadcast_setup_oneshot(),
or should be cleared only conditionally, or some other solution is
needed. Anyway, patch make the warning gone on my hacked setup, I was
waiting for testing results on real C1E hardware.

Thanks
Stanislaw

diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index 43780ab..98977a5 100644
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -756,6 +756,7 @@ out:
 static void tick_broadcast_clear_oneshot(int cpu)
 {
 	cpumask_clear_cpu(cpu, tick_broadcast_oneshot_mask);
+	cpumask_clear_cpu(cpu, tick_broadcast_pending_mask);
 }

 static void tick_broadcast_init_next_event(struct cpumask *mask,
--
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