linux-kernel - Re: [PATCH 2/2] lockdep reentrancy

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Date:	Wed, 24 Jan 2007 11:55:00 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Andrew Morton <akpm@...l.org>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Christoph Hellwig <hch@...radead.org>,
	linux-kernel@...r.kernel.org, ltt-dev@...fik.org,
	"Martin J. Bligh" <mbligh@...igh.org>,
	Douglas Niehaus <niehaus@...s.ku.edu>,
	systemtap@...rces.redhat.com, Thomas Gleixner <tglx@...utronix.de>,
	Richard J Moore <richardj_moore@...ibm.com>
Subject: Re: [PATCH 2/2] lockdep reentrancy

Hi Andrew,

* Andrew Morton (akpm@...l.org) wrote:
> On Tue, 16 Jan 2007 12:56:31 -0500
> Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> wrote:
> 
> > Here is a patch to lockdep.c so it behaves correctly when a kprobe breakpoint is
> > put on a marker within hardirq tracing functions as long as the marker is within
> > the lockdep_recursion incremented boundaries. It should apply on 
> > 2.6.20-rc4-git3.
> > 
> > Mathieu
> > 
> > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
> > 
> > 
> > @@ -1841,33 +1843,36 @@ void trace_hardirqs_on(void)
> 
> You lost the patch headers.
> 
> >  	struct task_struct *curr = current;
> >  	unsigned long ip;
> >  
> >  	if (unlikely(!debug_locks || current->lockdep_recursion))
> >  		return;
> >  
> > +	current->lockdep_recursion++;
> > +	barrier();
> 
> Why can't we use lockdep_off() here?
> 

Because I thought that changing lockdep_off() for the whole system might be a
little different than adding a lockdep recursion protection. See my other email
for the lockdep_on/off() discussion.

And please drop this patch : It sometimes make lockdep trigger false positives
under heavy IRQ load because of a dropped lockdep event.

Mathieu


> >  	if (DEBUG_LOCKS_WARN_ON(unlikely(!early_boot_irqs_enabled)))
> > -		return;
> > +		goto end;
> >  
> >  	if (unlikely(curr->hardirqs_enabled)) {
> >  		debug_atomic_inc(&redundant_hardirqs_on);
> > -		return;
> > +		goto end;
> >  	}
> >  	/* we'll do an OFF -> ON transition: */
> >  	curr->hardirqs_enabled = 1;
> >  	ip = (unsigned long) __builtin_return_address(0);
> >  
> >  	if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
> > -		return;
> > +		goto end;
> >  	if (DEBUG_LOCKS_WARN_ON(current->hardirq_context))
> > -		return;
> > +		goto end;
> >  	/*
> >  	 * We are going to turn hardirqs on, so set the
> >  	 * usage bit for all held locks:
> >  	 */
> >  	if (!mark_held_locks(curr, 1, ip))
> > -		return;
> > +		goto end;
> >  	/*
> >  	 * If we have softirqs enabled, then set the usage
> >  	 * bit for all held locks. (disabled hardirqs prevented
> > @@ -1875,11 +1880,14 @@ void trace_hardirqs_on(void)
> >  	 */
> >  	if (curr->softirqs_enabled)
> >  		if (!mark_held_locks(curr, 0, ip))
> > -			return;
> > +			goto end;
> >  
> >  	curr->hardirq_enable_ip = ip;
> >  	curr->hardirq_enable_event = ++curr->irq_events;
> >  	debug_atomic_inc(&hardirqs_on_events);
> > +end:
> > +	barrier();
> > +	current->lockdep_recursion--;
> 
> lockdep_on()?
> 
> >  }
> >  
> >  EXPORT_SYMBOL(trace_hardirqs_on);
> > @@ -1888,14 +1896,17 @@ void trace_hardirqs_off(void)
> >  {
> >  	struct task_struct *curr = current;
> >  
> >  	if (unlikely(!debug_locks || current->lockdep_recursion))
> >  		return;
> >  
> > +	current->lockdep_recursion++;
> > +	barrier();
> 
> lockdep_off()?
> 
> >  	if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
> > -		return;
> > +		goto end;
> >  
> >  	if (curr->hardirqs_enabled) {
> >  		/*
> > @@ -1910,6 +1921,9 @@ void trace_hardirqs_off(void)
> >  		debug_atomic_inc(&hardirqs_off_events);
> >  	} else
> >  		debug_atomic_inc(&redundant_hardirqs_off);
> > +end:
> > +	barrier();
> > +	current->lockdep_recursion--;
> 
> lockdep_on()?

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