linux-kernel - Re: [PATCH] tracing: Fix lockdep warning in global

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Date:	Mon, 21 Dec 2009 10:49:51 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Li Zefan <lizf@...fujitsu.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing: Fix lockdep warning in global_clock()

On Mon, 2009-12-21 at 07:43 +0100, Ingo Molnar wrote:
> * Li Zefan <lizf@...fujitsu.com> wrote:
> 
> >  # echo 1 > events/enable
> >  # echo global > trace_clock
> > 
> > ------------[ cut here ]------------
> > WARNING: at kernel/lockdep.c:3162 check_flags+0xb2/0x190()
> > ...
> > ---[ end trace 3f86734a89416623 ]---
> > possible reason: unannotated irqs-on.
> > ...
> > 
> > Signed-off-by: Li Zefan <lizf@...fujitsu.com>
> > ---
> >  kernel/trace/trace_clock.c |    4 ++--
> >  1 files changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/kernel/trace/trace_clock.c b/kernel/trace/trace_clock.c
> > index 84a3a7b..11563c9 100644
> > --- a/kernel/trace/trace_clock.c
> > +++ b/kernel/trace/trace_clock.c
> > @@ -83,7 +83,7 @@ u64 notrace trace_clock_global(void)
> >  	int this_cpu;
> >  	u64 now;
> >  
> > -	raw_local_irq_save(flags);
> > +	local_irq_save(flags);
> 
> Hm, wont this cause problems when we trace inside lockdep? Have you tried the 
> lockdep events - do they still work?


Doesn't the lockdep code protect against this type of recursion.

Working with interrupts and spin locks in the latency code, I found that
I had to remove all the raw_local_irq_save for the normal
local_irq_save. Because if you disable interrupts with raw_* and then
anything that is called must also disable with raw_*, if they don't then
lockdep will blow up.

-- Steve


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