Re: clockevents_program_event WARN_ON preventing boot.

[Thomas Gleixner <tglx@linutronix.de>]

On Fri, 3 May 2013, Dave Jones wrote:
> On Fri, May 03, 2013 at 12:49:20AM +0200, Thomas Gleixner wrote:
> 
>  > I'm fundamentally confused and Daves observation about slub debug does
>  > not make it less confusing.
>  > 
>  > It'd be nice if you could add some more instrumentation or bisect the
>  > issue.
> 
> Here's what I ended up with..
> b352bc1cbc29134a356b5c16ee2281807a7b984e is the first bad commit
> commit b352bc1cbc29134a356b5c16ee2281807a7b984e
> Author: Thomas Gleixner <tglx@linutronix.de>
> Date:   Tue Mar 5 14:25:32 2013 +0100
> 
>     tick: Convert broadcast cpu bitmaps to cpumask_var_t
>     
>     Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
>     Link: http://lkml.kernel.org/r/20130306111537.366394000@linutronix.de
>     Cc: Rusty Russell <rusty@rustcorp.com.au>
> 

I bet you have CONFIG_CPUMASK_OFFSTACK enabled.

/me is a moron and rumages for a brown paperbag.

Patch below.

Thanks,

	tglx

------------>

Subject: tick: Use zalloc_cpumask_var for allocating offstack cpumasks
From: Thomas Gleixner <tglx@linutronix.de>
Date: Fri, 03 May 2013 20:22:36 +0200

commit b352bc1cbc (tick: Convert broadcast cpu bitmaps to
cpumask_var_t) broke CONFIG_CPUMASK_OFFSTACK in a very subtle way.

Instead of allocating the cpumasks with zalloc_cpumask_var it uses
alloc_cpumask_var, so we can get random data there, which of course
confuses the logic completely and causes random failures.

Reported-by: Dave Jones <davej@redhat.com>
Reported-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 kernel/time/tick-broadcast.c |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

Index: linux-2.6/kernel/time/tick-broadcast.c
===================================================================
--- linux-2.6.orig/kernel/time/tick-broadcast.c
+++ linux-2.6/kernel/time/tick-broadcast.c
@@ -785,11 +785,11 @@ bool tick_broadcast_oneshot_available(vo
 
 void __init tick_broadcast_init(void)
 {
-	alloc_cpumask_var(&tick_broadcast_mask, GFP_NOWAIT);
-	alloc_cpumask_var(&tmpmask, GFP_NOWAIT);
+	zalloc_cpumask_var(&tick_broadcast_mask, GFP_NOWAIT);
+	zalloc_cpumask_var(&tmpmask, GFP_NOWAIT);
 #ifdef CONFIG_TICK_ONESHOT
-	alloc_cpumask_var(&tick_broadcast_oneshot_mask, GFP_NOWAIT);
-	alloc_cpumask_var(&tick_broadcast_pending_mask, GFP_NOWAIT);
-	alloc_cpumask_var(&tick_broadcast_force_mask, GFP_NOWAIT);
+	zalloc_cpumask_var(&tick_broadcast_oneshot_mask, GFP_NOWAIT);
+	zalloc_cpumask_var(&tick_broadcast_pending_mask, GFP_NOWAIT);
+	zalloc_cpumask_var(&tick_broadcast_force_mask, GFP_NOWAIT);
 #endif
 }