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

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Date:	Mon, 13 Apr 2015 18:32:57 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Peter Zijlstra <peterz@...radead.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


* Peter Zijlstra <peterz@...radead.org> wrote:

> 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

Yeah. I'd also make it:

 	if (unlikely(!debug_locks))
 		return;

or such.

Thanks,

	Ingo
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