Re: [PATCH 2/2] rcu-tasks: add RCU-tasks self tests

[Uladzislau Rezki <urezki@gmail.com>]

On Mon, Dec 21, 2020 at 12:45:13PM -0800, Paul E. McKenney wrote:
> On Mon, Dec 21, 2020 at 08:48:48PM +0100, Uladzislau Rezki wrote:
> > On Mon, Dec 21, 2020 at 11:29:06AM -0800, Paul E. McKenney wrote:
> > > On Mon, Dec 21, 2020 at 07:45:39PM +0100, Uladzislau Rezki wrote:
> > > > On Mon, Dec 21, 2020 at 09:18:05AM -0800, Paul E. McKenney wrote:
> > > > > On Mon, Dec 21, 2020 at 04:38:09PM +0100, Uladzislau Rezki wrote:
> > > > > > On Wed, Dec 16, 2020 at 03:29:55PM -0800, Paul E. McKenney wrote:
> > > > > > > On Wed, Dec 16, 2020 at 04:49:59PM +0100, Uladzislau Rezki wrote:
> > > > > 
> > > > > [ . . . ]
> > > > > 
> > > > > > > > 2.20.1
> > > > > > > 
> > > > > > > Again, much improved!
> > > > > > > 
> > > > > > See below the v3 version. I hope i fixed all comments :)
> > > > > > 
> > > > > > >From 06f7adfd84cbb1994d0e2693ee9dcdfd272a9bd0 Mon Sep 17 00:00:00 2001
> > > > > > From: "Uladzislau Rezki (Sony)" <urezki@gmail.com>
> > > > > > Date: Wed, 9 Dec 2020 21:27:32 +0100
> > > > > > Subject: [PATCH v3 1/1] rcu-tasks: Add RCU-tasks self tests
> > > > > > 
> > > > > > This commit adds self tests for early-boot use of RCU-tasks grace periods.
> > > > > > It tests all three variants (Rude, Tasks, and Tasks Trace) and covers
> > > > > > both synchronous (e.g., synchronize_rcu_tasks()) and asynchronous (e.g.,
> > > > > > call_rcu_tasks()) grace-period APIs.
> > > > > > 
> > > > > > Self-tests are run only in kernels built with CONFIG_PROVE_RCU=y.
> > > > > > 
> > > > > > Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
> > > > > 
> > > > > Much better!
> > > > > 
> > > > > I pulled this in, but made one small additional change.  Please let me
> > > > > know if this is problematic.
> > > > > 
> > > > > 							Thanx, Paul
> > > > > 
> > > > > ------------------------------------------------------------------------
> > > > > 
> > > > > commit 93372198b5c9efdfd288aa3b3ee41c1f90866886
> > > > > Author: Uladzislau Rezki (Sony) <urezki@gmail.com>
> > > > > Date:   Wed Dec 9 21:27:32 2020 +0100
> > > > > 
> > > > >     rcu-tasks: Add RCU-tasks self tests
> > > > >     
> > > > >     This commit adds self tests for early-boot use of RCU-tasks grace periods.
> > > > >     It tests all three variants (Rude, Tasks, and Tasks Trace) and covers
> > > > >     both synchronous (e.g., synchronize_rcu_tasks()) and asynchronous (e.g.,
> > > > >     call_rcu_tasks()) grace-period APIs.
> > > > >     
> > > > >     Self-tests are run only in kernels built with CONFIG_PROVE_RCU=y.
> > > > >     
> > > > >     Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
> > > > >     Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> > > > > 
> > > > > diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> > > > > index 3660755..35a2cd5 100644
> > > > > --- a/kernel/rcu/tasks.h
> > > > > +++ b/kernel/rcu/tasks.h
> > > > > @@ -1224,6 +1224,40 @@ void show_rcu_tasks_gp_kthreads(void)
> > > > >  }
> > > > >  #endif /* #ifndef CONFIG_TINY_RCU */
> > > > >  
> > > > > +struct rcu_tasks_test_desc {
> > > > > +	struct rcu_head rh;
> > > > > +	const char *name;
> > > > > +	bool notrun;
> > > > > +};
> > > > > +
> > > > > +static struct rcu_tasks_test_desc tests[] = {
> > > > > +	{
> > > > > +		.name = "call_rcu_tasks()",
> > > > > +		/* If not defined, the test is skipped. */
> > > > > +		.notrun = !IS_ENABLED(CONFIG_TASKS_RCU),
> > > > > +	},
> > > > > +	{
> > > > > +		.name = "call_rcu_tasks_rude()",
> > > > > +		/* If not defined, the test is skipped. */
> > > > > +		.notrun = !IS_ENABLED(CONFIG_TASKS_RUDE_RCU),
> > > > > +	},
> > > > > +	{
> > > > > +		.name = "call_rcu_tasks_trace()",
> > > > > +		/* If not defined, the test is skipped. */
> > > > > +		.notrun = !IS_ENABLED(CONFIG_TASKS_TRACE_RCU)
> > > > > +	}
> > > > > +};
> > > > > +
> > > > > +static void test_rcu_tasks_callback(struct rcu_head *rhp)
> > > > > +{
> > > > > +	struct rcu_tasks_test_desc *rttd =
> > > > > +		container_of(rhp, struct rcu_tasks_test_desc, rh);
> > > > > +
> > > > > +	pr_info("Callback from %s invoked.\n", rttd->name);
> > > > That is fine! We can output the name instead of executed counter.
> > > > Doing so makes it completely clear who triggers the callback.
> > > 
> > > And we also need to make it not trigger when CONFIG_PROVE_RCU=n.
> > > While in the area, we might as well leave anything that is needed only
> > > by CONFIG_PROVE_RCU=y undefined when CONFIG_PROVE_RCU=n.
> > > 
> > > How about the following?
> > > 
> > > 							Thanx, Paul
> > > 
> > > ------------------------------------------------------------------------
> > > 
> > > commit f7a1ac0d3504e0518745da7f98573c1b13587f3e
> > > Author: Uladzislau Rezki (Sony) <urezki@gmail.com>
> > > Date:   Wed Dec 9 21:27:32 2020 +0100
> > > 
> > >     rcu-tasks: Add RCU-tasks self tests
> > >     
> > >     This commit adds self tests for early-boot use of RCU-tasks grace periods.
> > >     It tests all three variants (Rude, Tasks, and Tasks Trace) and covers
> > >     both synchronous (e.g., synchronize_rcu_tasks()) and asynchronous (e.g.,
> > >     call_rcu_tasks()) grace-period APIs.
> > >     
> > >     Self-tests are run only in kernels built with CONFIG_PROVE_RCU=y.
> > >     
> > >     Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
> > >     [ paulmck: Handle CONFIG_PROVE_RCU=n and identify test cases' callbacks. ]
> > >     Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> > > 
> > > diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> > > index 3660755..af7c194 100644
> > > --- a/kernel/rcu/tasks.h
> > > +++ b/kernel/rcu/tasks.h
> > > @@ -1224,6 +1224,82 @@ void show_rcu_tasks_gp_kthreads(void)
> > >  }
> > >  #endif /* #ifndef CONFIG_TINY_RCU */
> > >  
> > > +#ifdef CONFIG_PROVE_RCU
> > > +struct rcu_tasks_test_desc {
> > > +	struct rcu_head rh;
> > > +	const char *name;
> > > +	bool notrun;
> > > +};
> > > +
> > > +static struct rcu_tasks_test_desc tests[] = {
> > > +	{
> > > +		.name = "call_rcu_tasks()",
> > > +		/* If not defined, the test is skipped. */
> > > +		.notrun = !IS_ENABLED(CONFIG_TASKS_RCU),
> > > +	},
> > > +	{
> > > +		.name = "call_rcu_tasks_rude()",
> > > +		/* If not defined, the test is skipped. */
> > > +		.notrun = !IS_ENABLED(CONFIG_TASKS_RUDE_RCU),
> > > +	},
> > > +	{
> > > +		.name = "call_rcu_tasks_trace()",
> > > +		/* If not defined, the test is skipped. */
> > > +		.notrun = !IS_ENABLED(CONFIG_TASKS_TRACE_RCU)
> > > +	}
> > > +};
> > > +
> > > +static void test_rcu_tasks_callback(struct rcu_head *rhp)
> > > +{
> > > +	struct rcu_tasks_test_desc *rttd =
> > > +		container_of(rhp, struct rcu_tasks_test_desc, rh);
> > > +
> > > +	pr_info("Callback from %s invoked.\n", rttd->name);
> > > +
> > > +	rttd->notrun = true;
> > > +}
> > > +
> > > +static void rcu_tasks_initiate_self_tests(void)
> > > +{
> > > +	pr_info("Running RCU-tasks wait API self tests\n");
> > > +#ifdef CONFIG_TASKS_RCU
> > > +	synchronize_rcu_tasks();
> > > +	call_rcu_tasks(&tests[0].rh, test_rcu_tasks_callback);
> > > +#endif
> > > +
> > > +#ifdef CONFIG_TASKS_RUDE_RCU
> > > +	synchronize_rcu_tasks_rude();
> > > +	call_rcu_tasks_rude(&tests[1].rh, test_rcu_tasks_callback);
> > > +#endif
> > > +
> > > +#ifdef CONFIG_TASKS_TRACE_RCU
> > > +	synchronize_rcu_tasks_trace();
> > > +	call_rcu_tasks_trace(&tests[2].rh, test_rcu_tasks_callback);
> > > +#endif
> > > +}
> > > +
> > > +static int rcu_tasks_verify_self_tests(void)
> > > +{
> > > +	int ret = 0;
> > > +	int i;
> > > +
> > > +	for (i = 0; i < ARRAY_SIZE(tests); i++) {
> > > +		if (!tests[i].notrun) {		// still hanging.
> > > +			pr_err("%s has been failed.\n", tests[i].name);
> > > +			ret = -1;
> > > +		}
> > > +	}
> > > +
> > > +	if (ret)
> > > +		WARN_ON(1);
> > > +
> > > +	return ret;
> > > +}
> > > +late_initcall(rcu_tasks_verify_self_tests);
> > > +#else /* #ifdef CONFIG_PROVE_RCU */
> > > +static void rcu_tasks_initiate_self_tests(void) { }
> > > +#endif /* #else #ifdef CONFIG_PROVE_RCU */
> > > +
> > >  void __init rcu_init_tasks_generic(void)
> > >  {
> > >  #ifdef CONFIG_TASKS_RCU
> > > @@ -1237,6 +1313,9 @@ void __init rcu_init_tasks_generic(void)
> > >  #ifdef CONFIG_TASKS_TRACE_RCU
> > >  	rcu_spawn_tasks_trace_kthread();
> > >  #endif
> > > +
> > > +	// Run the self-tests.
> > > +	rcu_tasks_initiate_self_tests();
> > >  }
> > >  
> > >  #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
> > That makes sense to me. I missed that point. There is no
> > reason in wasting of extra cycles which affect a boot up
> > time if built without CONFIG_PROVE_RCU.
> 
> If CONFIG_PROVE_RCU=n, then rcu_tasks_initiate_self_tests is an empty
> function.  So the compiler should be able to eliminate all runtime
> overhead from rcu_tasks_initiate_self_tests() when CONFIG_PROVE_RCU=n.
> 
> Or am I missing your point?
> 
That is correct, i mean your description. I wanted to underline
that the late_initcall(rcu_tasks_verify_self_tests); was called
even for CONFIG_PROVE_RCU=n, what would affect a boot time with
disabled option. Of-course that extra time would be negligible.
From the other hand, why we should introduce it if it can be
avoided.

Your last change fixes that :)

--
Vlad Rezki