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

[Josh Triplett <josh@joshtriplett.org>]

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.

> @@ -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.)

- Josh Triplett