linux-kernel - Re: [PATCH 5/6] [x86] watchdog: move trigger_all_cpu_backtrace to its own die

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Date:	Wed, 21 Apr 2010 23:34:36 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Don Zickus <dzickus@...hat.com>
Cc:	mingo@...e.hu, peterz@...radead.org, gorcunov@...il.com,
	aris@...hat.com, linux-kernel@...r.kernel.org,
	randy.dunlap@...cle.com
Subject: Re: [PATCH 5/6] [x86] watchdog: move trigger_all_cpu_backtrace to
	its own die_notifier

On Wed, Apr 21, 2010 at 05:10:12PM -0400, Don Zickus wrote:
> On Wed, Apr 21, 2010 at 11:00:04PM +0200, Frederic Weisbecker wrote:
> > On Tue, Apr 20, 2010 at 11:24:02AM -0400, Don Zickus wrote:
> > > As part of the transition of the nmi watchdog to something more generic,
> > > the trigger_all_cpu_backtrace code is getting left behind.  Put it in its
> > > own die_notifier so it can still be used.
> > > 
> > > Signed-off-by: Don Zickus <dzickus@...hat.com>
> > > ---
> > >  arch/x86/kernel/apic/hw_nmi.c |   65 ++++++++++++++++++++++++++++++++---------
> > >  1 files changed, 51 insertions(+), 14 deletions(-)
> > > 
> > > diff --git a/arch/x86/kernel/apic/hw_nmi.c b/arch/x86/kernel/apic/hw_nmi.c
> > > index 79425f9..19d3435 100644
> > > --- a/arch/x86/kernel/apic/hw_nmi.c
> > > +++ b/arch/x86/kernel/apic/hw_nmi.c
> > > @@ -17,6 +17,10 @@
> > >  #include <linux/cpumask.h>
> > >  #include <linux/kernel_stat.h>
> > >  #include <asm/mce.h>
> > > +#include <linux/kdebug.h>
> > > +#include <linux/notifier.h>
> > > +#include <linux/kprobes.h>
> > > +
> > >  
> > >  #include <linux/nmi.h>
> > >  #include <linux/module.h>
> > > @@ -54,20 +58,6 @@ int hw_nmi_is_cpu_stuck(struct pt_regs *regs)
> > >  	unsigned int sum;
> > >  	int cpu = smp_processor_id();
> > >  
> > > -	/* FIXME: cheap hack for this check, probably should get its own
> > > -	 * die_notifier handler
> > > -	 */
> > > -	if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
> > > -		static DEFINE_SPINLOCK(lock);	/* Serialise the printks */
> > > -
> > > -		spin_lock(&lock);
> > > -		printk(KERN_WARNING "NMI backtrace for cpu %d\n", cpu);
> > > -		show_regs(regs);
> > > -		dump_stack();
> > > -		spin_unlock(&lock);
> > > -		cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
> > > -	}
> > > -
> > >  	/* if we are doing an mce, just assume the cpu is not stuck */
> > >  	/* Could check oops_in_progress here too, but it's safer not to */
> > >  	if (mce_in_progress())
> > > @@ -109,6 +99,53 @@ void arch_trigger_all_cpu_backtrace(void)
> > >  		mdelay(1);
> > >  	}
> > >  }
> > > +
> > > +static int __kprobes
> > > +arch_trigger_all_cpu_backtrace_handler(struct notifier_block *self,
> > > +			 unsigned long cmd, void *__args)
> > > +{
> > > +	struct die_args *args = __args;
> > > +	struct pt_regs *regs;
> > > +	int cpu = smp_processor_id();
> > > +
> > > +	switch (cmd) {
> > > +	case DIE_NMI:
> > > +	case DIE_NMI_IPI:
> > > +		break;
> > > +
> > > +	default:
> > > +		return NOTIFY_DONE;
> > > +	}
> > > +
> > > +	regs = args->regs;
> > > +
> > > +	if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
> > > +		static DEFINE_SPINLOCK(lock);	/* Serialise the printks */
> > > +
> > > +		spin_lock(&lock);
> > 
> > 
> > 
> > This should be an arch_spin_lock(), so that it won't sleep with rt mutex.
> 
> ok, I just copied and pasted what was there currently.
> 
> > 
> > 
> > In fact this whole function can be moved to generic code, right?
> 
> generic for x86, yes.  Ingo stuck in the nmi.c code awhile ago.  This code
> just needs a home somewhere.  I really don't care where.


Ah right, this is x86 only, sorry.

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