Re: [PATCH tip/core/rcu 1/5] rcu: Add duplicate-callback tests to rcutorture

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Sat, Aug 17, 2013 at 07:54:20PM -0700, Josh Triplett wrote:
> On Sat, Aug 17, 2013 at 07:25:13PM -0700, Paul E. McKenney wrote:
> > From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> > 
> > This commit adds a object_debug option to rcutorture to allow the
> > debug-object-based checks for duplicate call_rcu() invocations to
> > be deterministically tested.
> > 
> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> > Cc: Sedat Dilek <sedat.dilek@gmail.com>
> > Cc: Davidlohr Bueso <davidlohr.bueso@hp.com>
> > Cc: Rik van Riel <riel@surriel.com>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Cc: Linus Torvalds <torvalds@linux-foundation.org>
> > Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
> 
> Two comments below; with those fixed,
> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
> 
> > ---
> > @@ -100,6 +101,8 @@ module_param(fqs_stutter, int, 0444);
> >  MODULE_PARM_DESC(fqs_stutter, "Wait time between fqs bursts (s)");
> >  module_param(n_barrier_cbs, int, 0444);
> >  MODULE_PARM_DESC(n_barrier_cbs, "# of callbacks/kthreads for barrier testing");
> > +module_param(object_debug, int, 0444);
> > +MODULE_PARM_DESC(object_debug, "Enable debug-object double call_rcu() testing");
> 
> modules-next has a change to ignore and warn about
> unknown module parameters.  Thus, I'd suggest wrapping the ifdef around
> this module parameter, so it doesn't exist at all without
> CONFIG_DEBUG_OBJECTS_RCU_HEAD.
> 
> Alternatively, consider providing the test unconditionally, and just
> printing a big warning message saying that it's going to cause
> corruption in the !CONFIG_DEBUG_OBJECTS_RCU_HEAD case.

I currently do something like the above.  The module parameter
is defined unconditionally, but the actual tests are under #ifdef
CONFIG_DEBUG_OBJECTS_RCU_HEAD.  If you specify object_debug for a
!CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel, the pr_alert() below happens,
and the test is omitted, thus avoiding the list corruption.

Seem reasonable?

> > @@ -2163,6 +2178,28 @@ rcu_torture_init(void)
> >  		firsterr = retval;
> >  		goto unwind;
> >  	}
> > +	if (object_debug) {
> > +#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
> > +		struct rcu_head rh1;
> > +		struct rcu_head rh2;
> > +
> > +		init_rcu_head_on_stack(&rh1);
> > +		init_rcu_head_on_stack(&rh2);
> > +		pr_alert("rcutorture: WARN: Duplicate call_rcu() test starting.\n");
> > +		local_irq_disable(); /* Make it hard to finish grace period. */
> > +		call_rcu(&rh1, rcu_torture_leak_cb); /* start grace period. */
> > +		call_rcu(&rh2, rcu_torture_err_cb);
> > +		call_rcu(&rh2, rcu_torture_err_cb); /* duplicate callback. */
> > +		local_irq_enable();
> > +		rcu_barrier();
> > +		pr_alert("rcutorture: WARN: Duplicate call_rcu() test complete.\n");
> > +		destroy_rcu_head_on_stack(&rh1);
> > +		destroy_rcu_head_on_stack(&rh2);
> > +#else /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
> > +		pr_alert("rcutorture: !%s, not testing duplicate call_rcu()\n",
> > +			 "CONFIG_DEBUG_OBJECTS_RCU_HEAD");
> 
> Why put this parameter in a separate string?  That makes it harder to
> grep for the full error message.  (That's assuming you keep the error
> message, given the comment above.)

Force of habit, fixed.  ;-)

							Thanx, Paul