linux-kernel - Re: [PATCH v5 01/10] module: Sanitize RCU usage and locking

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Message-ID: <20150413154002.GI23123@twins.programming.kicks-ass.net>
Date:	Mon, 13 Apr 2015 17:40:02 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	rusty@...tcorp.com.au, mathieu.desnoyers@...icios.com,
	oleg@...hat.com, paulmck@...ux.vnet.ibm.com,
	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	andi@...stfloor.org, rostedt@...dmis.org, tglx@...utronix.de,
	laijs@...fujitsu.com, linux@...izon.com
Subject: Re: [PATCH v5 01/10] module: Sanitize RCU usage and locking

On Mon, Apr 13, 2015 at 05:32:29PM +0200, Ingo Molnar wrote:
> > +static void module_assert_mutex_or_preempt(void)
> > +{
> > +#ifdef CONFIG_LOCKDEP
> > +	int rcu_held = rcu_read_lock_sched_held();
> > +	int mutex_held = 1;
> > +
> > +	if (debug_locks)
> > +		mutex_held = lockdep_is_held(&module_mutex);
> > +
> > +	WARN_ON(!rcu_held && !mutex_held);
> 
> So because rcu_read_lock_sched_held() also depends on debug_locks 
> being on to be fully correct, shouldn't the warning also be within the 
> debug_locks condition?

Ah, see how mutex_held will be true for !debug_locks and therefore we'll
not trigger the warn.

Maybe not the best way to code that though.

Something like so perhaps:

static void module_assert_mutex_or_preempt(void)
{
#ifdef CONFIG_LOCKDEP
	if (!debug_locks)
		return;

	WARN_ON(!rcu_held_lock_sched_held() &&
		!lockdep_is_held(&module_mutex));
#endif
}
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