linux-kernel - Re: sys_sched_yield keeps locked irq before call of schedule()

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Message-ID: <alpine.DEB.1.10.0811060845340.31011@gandalf.stny.rr.com>
Date:	Thu, 6 Nov 2008 08:46:39 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Zdenek Kabelac <zdenek.kabelac@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: sys_sched_yield keeps locked irq before call of schedule()


On Thu, 6 Nov 2008, Ingo Molnar wrote:
> 
> * Zdenek Kabelac <zdenek.kabelac@...il.com> wrote:
> 
> > > is this some special warning you added? The stock kernel certainly 
> > > does not emit this warning.
> > 
> > Yes - it's my personal debug checker that tries to watch wether irq 
> > & irqsafe are running in pair. So it shows a warning if there is a 
> > call of spin_lock_irq and irq is already dissabled.
> 
> btw., i have added lockdep instrumentation for this two years ago, 
> it's in the upstream kernel:
> 
> /proc/lockdep_stats: redundant hardirq ons:                7744
> /proc/lockdep_stats: redundant hardirq offs:            1873736
> /proc/lockdep_stats: redundant softirq ons:                   0
> /proc/lockdep_stats: redundant softirq offs:                  0
> 
> you could extend the code to trace it. See 
> kernel/lockdep.c:trace_hardirqs_on_caller(). This bit does it:
> 
>         if (unlikely(curr->hardirqs_enabled)) {
>                 debug_atomic_inc(&redundant_hardirqs_on);
>                 return;
>         }
> 
> you could add a ftrace_printk("redundant hardirq") call right there, 
> enable ftrace, and enable stack tracing of each trace entry:

Quick note. Currently ftrace_printk only shows up if it is set in the 
iter_ctrl.

  echo trace_printk > /debug/tracing/iter_ctrl

I'll send out a patch to have it on by default.

-- Steve

> 
>  echo stacktrace > /debug/tracing/iter_ctrl
> 
> then you should see all the call sites in /debug/tracing/trace.
> 
> 	Ingo
> 
> 
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