linux-kernel - Re: [RFC patch 17/18] MIPS : Trace clock

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Date:	Fri, 7 Nov 2008 12:44:46 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	akpm@...ux-foundation.org, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org, Ralf Baechle <ralf@...ux-mips.org>
Subject: Re: [RFC patch 17/18] MIPS : Trace clock

* Peter Zijlstra (a.p.zijlstra@...llo.nl) wrote:
> On Fri, 2008-11-07 at 00:23 -0500, Mathieu Desnoyers wrote:
> > Note for Peter Zijlstra :
> > You should probably have a look at lockdep.c raw_spinlock_t lockdep_lock usage.
> > I suspect it may be used with preemption enabled in graph_lock(). (not sure
> > though, but it's worth double-checking.
> 
> Are you worried about the graph_lock() instance in
> lookup_chain_cache() ?
> 
> That is the locking for validate_chain,
> 
> __lock_acquire()
>  validate_chain()
>    look_up_chain_cache()
>      graph_lock()
>    check_prevs_add()
>      check_prev_add()
>        graph_unlock()
>        graph_lock()
>    graph_unlock()
> 
> which is all done without modifying IRQ state.
> 
> However, __lock_acquire() is only called with IRQs disabled:
> 
> lock_acquire()
>   raw_local_irq_save()
>   __lock_acquire()
> 
> lock_release()
>   raw_local_irq_save()
>   __lock_release()
>     lock_release_nested()
>       __lock_acquire()
>     lock_release_non_nested()
>       __lock_acquire()
> 
> lock_set_subclass()
>   raw_local_irq_save()
>   __lock_set_subclass()
>     __lock_acquire()
> 
> So I think we're good.
> 

Yep, looks good.

Mathieu


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Mathieu Desnoyers
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