linux-kernel - Re: [PATCH RFC tip/core/rcu 37/41] lockdep: Add CPU-idle/offline warning to lockdep-RCU splat

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Message-ID: <20120203061225.GD3008@leaf>
Date:	Thu, 2 Feb 2012 22:12:25 -0800
From:	Josh Triplett <josh@...htriplett.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
	fweisbec@...il.com, patches@...aro.org,
	"Paul E. McKenney" <paul.mckenney@...aro.org>
Subject: Re: [PATCH RFC tip/core/rcu 37/41] lockdep: Add CPU-idle/offline
 warning to lockdep-RCU splat

On Thu, Feb 02, 2012 at 10:30:07AM -0800, Paul E. McKenney wrote:
> On Wed, Feb 01, 2012 at 10:07:52PM -0800, Josh Triplett wrote:
> > On Wed, Feb 01, 2012 at 11:41:55AM -0800, Paul E. McKenney wrote:
> > > --- a/kernel/lockdep.c
> > > +++ b/kernel/lockdep.c
> > > @@ -4176,7 +4176,13 @@ void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
> > >  	printk("-------------------------------\n");
> > >  	printk("%s:%d %s!\n", file, line, s);
> > >  	printk("\nother info that might help us debug this:\n\n");
> > > -	printk("\nrcu_scheduler_active = %d, debug_locks = %d\n", rcu_scheduler_active, debug_locks);
> > > +	printk("\n%srcu_scheduler_active = %d, debug_locks = %d\n",
> > > +	       !rcu_lockdep_current_cpu_online()
> > > +			? "RCU used illegally from offline CPU!\n"
> > > +			: rcu_is_cpu_idle()
> > > +				? "RCU used illegally from idle CPU!\n"
> > > +				: "",
> > 
> > Not the usual way I've seen chained ?: indented in kernel code:
> > 
> >  cond1 ? value1 :
> >  cond2 ? value2 :
> >  value3
> > 
> > That avoids repeated indentation over to the right, much like "else if".
> 
> I tried the following, but didn't like it:
> 
> 	       !rcu_lockdep_current_cpu_online() ? "RCU used illegally from offline CPU!\n" :
> 	       rcu_is_cpu_idle() ? "RCU used illegally from idle CPU!\n" :
> 	       "",

Seems like an improvement to me, but it also doesn't matter enough to
bikeshed further about. :)

- Josh Triplett
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