linux-kernel - Re: [PATCH tip/core/rcu 01/15] rcu: Add PROVE_RCU

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Date:	Fri, 07 Sep 2012 08:54:33 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	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, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, rostedt@...dmis.org,
	Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com, fweisbec@...il.com,
	sbw@....edu, patches@...aro.org,
	"Paul E. McKenney" <paul.mckenney@...aro.org>
Subject: Re: [PATCH tip/core/rcu 01/15] rcu: Add PROVE_RCU_DELAY to provoke
 difficult races

On Thu, 2012-09-06 at 13:51 -0700, Paul E. McKenney wrote:
> On Thu, Sep 06, 2012 at 04:38:32PM +0200, Peter Zijlstra wrote:
> > On Thu, 2012-08-30 at 11:56 -0700, Paul E. McKenney wrote:
> > > +#ifdef CONFIG_PROVE_RCU_DELAY
> > > +               udelay(10); /* Make preemption more probable. */
> > 		cond_resched(); /* for extra fun? */
> 
> The additional fun could include "scheduling while atomic", so I will
> pass.  ;-)
> 
> (The problem is that __rcu_read_unlock() can be called with interrupts
> disabled, among other things.)

Hmm, too bad. Without a preemption point here you're relying on forced
preemption, which of course can only happen on PREEMPT=y kernels.

> > > +#endif /* #ifdef CONFIG_PROVE_RCU_DELAY */ 
> > 
> > 
> 

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