linux-kernel - Re: [PATCH RFC tip/core/rcu 05/11] rcu: add comment saying why DEBUG_OBJECTS_RCU

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Message-ID: <1298472914.7666.85.camel@gandalf.stny.rr.com>
Date:	Wed, 23 Feb 2011 09:55:14 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com
Subject: Re: [PATCH RFC tip/core/rcu 05/11] rcu: add comment saying why
 DEBUG_OBJECTS_RCU_HEAD depends on PREEMPT.

On Wed, 2011-02-23 at 08:59 -0500, Mathieu Desnoyers wrote:

> #ifdef CONFIG_PREEMPT
>                 /*
>                  * Ensure that queued callbacks are all executed.
>                  * If we detect that we are nested in a RCU read-side
>                  * critical
>                  * section, we should simply fail, otherwise we would
>                  * deadlock.
>                  */
>                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
>                     irqs_disabled()) {
>                         WARN_ON(1);
>                         return 0;
>                 }
>                 rcu_barrier();
>                 rcu_barrier_sched();
>                 rcu_barrier_bh();
>                 debug_object_init(head, &rcuhead_debug_descr);
>                 return 1;
> #else
> 		return 0;
> #endif
> 
> instead, no ?

BTW, if you do end up doing such a thing...

#ifndef CONFIG_PREEMPT
	return 0;
#endif

before all that would be much cleaner.

Just make sure any non defined in PREEMPT macros/functions are defined
as nops in !CONFIG_PREEMPT

-- Steve


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