linux-kernel - Re: bug: ftrace & lockdep badness

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Date:	Wed, 5 Nov 2008 12:13:01 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Heiko Carstens <heiko.carstens@...ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org
Subject: Re: bug: ftrace & lockdep badness


On Wed, 5 Nov 2008, Ingo Molnar wrote:
> > > 
> > > > This is the type of problems we deal with when we have the tracer 
> > > > tracing lockdep code at the same time the lockdep code is checking 
> > > > the tracer.
> > > 
> > > ok ... you are right, i guess we need to go back to raw locks after 
> > > all?
> > 
> > I do like the fact that lockdep checks it too. But there's times 
> > that we can not do that.
> > 
> > Perhaps we can do something in between.
> > 
> > Make a rb_spin_lock macro inside ring_buffer.c that can be either a 
> > spin_lock or a raw_spin_lock.  There are some tracers that must have 
> > this as a raw (function trace, irqsoff and preemptoff), but the rest 
> > should be fine. We can make it where the rb_spin_lock is a raw lock 
> > when any of those three tracers are configured, and make it into a 
> > normal lock when they are not.
> > 
> > This way we can still test the integrity of the ring_buffer for 
> > other tracers. We just need to be careful when we are using function 
> > tracing or irqs/preempt off tracing. But we need to be careful with 
> > those anyway.
> 
> i'd rather we not complicate this anymore and just go for raw locks 
> unconditionally - or no raw locks unconditionally.

OK, agree. We can have a debug patch that converts it back to normal 
spinlocks that we can apply when we want to test it. But for release, we 
just keep the raw_spin_locks.

-- Steve

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