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

[Uladzislau Rezki]

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:
> > > Add self tests for checking of RCU-tasks API functionality.
> > > It covers:
> > >     - wait API functions;
> > >     - invoking/completion call_rcu_tasks*().
> > > 
> > > Self-tests are run when CONFIG_PROVE_RCU kernel parameter is set.
> > > 
> > > Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
> > > ---
> > >  kernel/rcu/tasks.h | 44 ++++++++++++++++++++++++++++++++++++++++++++
> > >  1 file changed, 44 insertions(+)
> > > 
> > > diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> > > index 67a162949763..9407772780c1 100644
> > > --- a/kernel/rcu/tasks.h
> > > +++ b/kernel/rcu/tasks.h
> > > @@ -1225,6 +1225,16 @@ void show_rcu_tasks_gp_kthreads(void)
> > >  }
> > >  #endif /* #ifndef CONFIG_TINY_RCU */
> > >  
> > > +static struct rcu_head rhp;
> > > +static int rcu_execurted_test_counter;
> > > +static int rcu_run_test_counter;
> > > +
> > > +static void test_rcu_tasks_callback(struct rcu_head *r)
> > > +{
> > > +	pr_info("RCU-tasks test callback executed %d\n",
> > > +		++rcu_execurted_test_counter);
> > > +}
> > > +
> > >  void __init rcu_init_tasks_generic(void)
> > >  {
> > >  #ifdef CONFIG_TASKS_RCU
> > > @@ -1238,7 +1248,41 @@ void __init rcu_init_tasks_generic(void)
> > >  #ifdef CONFIG_TASKS_TRACE_RCU
> > >  	rcu_spawn_tasks_trace_kthread();
> > >  #endif
> > > +
> > > +	if (IS_ENABLED(CONFIG_PROVE_RCU)) {
> > > +		pr_info("Running RCU-tasks wait API self tests\n");
> > > +#ifdef CONFIG_TASKS_RCU
> > > +		rcu_run_test_counter++;
> > > +		call_rcu_tasks(&rhp, test_rcu_tasks_callback);
> > > +		synchronize_rcu_tasks();
> > > +#endif
> > > +
> > > +#ifdef CONFIG_TASKS_RUDE_RCU
> > > +		rcu_run_test_counter++;
> > > +		call_rcu_tasks_trace(&rhp, test_rcu_tasks_callback);
> > > +		synchronize_rcu_tasks_rude();
> > > +#endif
> > > +
> > > +#ifdef CONFIG_TASKS_TRACE_RCU
> > > +		rcu_run_test_counter++;
> > > +		call_rcu_tasks_trace(&rhp, test_rcu_tasks_callback);
> > > +		synchronize_rcu_tasks_trace();
> > > +#endif
> > > +	}
> > > +}
> > > +
> > > +static int rcu_tasks_verify_self_tests(void)
> > > +{
> > > +	int ret = 0;
> > > +
> > > +	if (rcu_run_test_counter != rcu_execurted_test_counter) {
> > > +		WARN_ON(1);
> > > +		ret = -1;
> > > +	}
> > > +
> > > +	return ret;
> > >  }
> > > +late_initcall(rcu_tasks_verify_self_tests);
> > >  
> > >  #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
> > >  static inline void rcu_tasks_bootup_oddness(void) {}
> > Please find a v2 of the patch that is in question. First version
> > uses the same rhp for all RCU flavors what is wrong. Initially
> > i had three different one per one flavor. But for some reason
> > end up with only one.
> > 
> > 
> > >From e7c6096af5a7916f29c0b4b05e1644b3b3a6c589 Mon Sep 17 00:00:00 2001
> > From: "Uladzislau Rezki (Sony)" <urezki@xxxxxxxxx>
> > Date: Wed, 9 Dec 2020 21:27:32 +0100
> > Subject: [PATCH v2 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@xxxxxxxxx>
> 
> Much improved, thank you!  A few more comments below.
> 
> > ---
> >  kernel/rcu/tasks.h | 69 ++++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 69 insertions(+)
> > 
> > diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> > index 36607551f966..7478d912734a 100644
> > --- a/kernel/rcu/tasks.h
> > +++ b/kernel/rcu/tasks.h
> > @@ -1224,6 +1224,35 @@ void show_rcu_tasks_gp_kthreads(void)
> >  }
> >  #endif /* #ifndef CONFIG_TINY_RCU */
> > 
> > +struct test_desc {
> 
> Please use something like "struct rcu_tasks_test_desc" to help the poor
> people who might need to grep for this.  Feel free to shorten it, but
> please make it descriptive and thus more likely to stay unique.
> 
> > +       struct rcu_head rh;
> > +       const char *name;
> > +       bool run;
> 
> If you make this "bool notrun" you don't need to initialize.
> 
> > +};
> > +
> > +static struct test_desc tests[] = {
> > +       { .name = "call_rcu_tasks()" },
> > +       { .name = "call_rcu_rude()"  },
> > +       { .name = "call_rcu_trace()" },
> > +};
> > +
> > +static int rcu_executed_test_counter;
> > +
> > +static void test_rcu_tasks_callback(struct rcu_head *rhp)
> > +{
> 
> 	struct rcu_tasks_test_desc *rttdp;
> 
> > +       int i;
> > +
> > +       pr_info("RCU-tasks test callback executed %d\n",
> > +               ++rcu_executed_test_counter);
> 
> 	rttdp = container_of(rhp, rh, struct rcu_tasks_test_desc);
> 	rttdp->notrun = true;
> 
> Or I suppose:
> 
> 	container_of(rhp, rh, struct rcu_tasks_test_desc)->notrun = true;
> 
> Then the loop below can go away.
> 
> > +
> > +       for (i = 0; i < ARRAY_SIZE(tests); i++) {
> > +               if (rhp == &tests[i].rh) {
> > +                       tests[i].run = false;
> > +                       break;
> > +               }
> > +       }
> > +}
> > +
> >  void __init rcu_init_tasks_generic(void)
> >  {
> >  #ifdef CONFIG_TASKS_RCU
> > @@ -1237,7 +1266,47 @@ void __init rcu_init_tasks_generic(void)
> >  #ifdef CONFIG_TASKS_TRACE_RCU
> >         rcu_spawn_tasks_trace_kthread();
> >  #endif
> > +
> > +       // Run the self-tests.
> > +       if (IS_ENABLED(CONFIG_PROVE_RCU)) {
> > +               pr_info("Running RCU-tasks wait API self tests\n");
> > +#ifdef CONFIG_TASKS_RCU
> > +               tests[0].run = true;
> 
> The s/run/notrun/ allows the three initializations of .run to go away.
> 
> > +               call_rcu_tasks(&tests[0].rh, test_rcu_tasks_callback);
> > +               synchronize_rcu_tasks();
> 
> Why not reverse the order of these two statements?  That would test
> call_rcu_tasks*()'s ability to do a grace period on their own, without
> help from the corresponding synchronize_rcu_tasks*().
> 
> > +#endif
> > +
> > +#ifdef CONFIG_TASKS_RUDE_RCU
> > +               tests[1].run = true;
> > +               call_rcu_tasks_rude(&tests[1].rh, test_rcu_tasks_callback);
> > +               synchronize_rcu_tasks_rude();
> > +#endif
> > +
> > +#ifdef CONFIG_TASKS_TRACE_RCU
> > +               tests[2].run = true;
> > +               call_rcu_tasks_trace(&tests[2].rh, test_rcu_tasks_callback);
> > +               synchronize_rcu_tasks_trace();
> > +#endif
> > +       }
> > +}
> > +
> > +static int rcu_tasks_verify_self_tests(void)
> > +{
> > +       int ret, i;
> 
> Why not initialize "ret" in the declaration?
> 
> > +
> > +       for (i = 0, ret = 0; i < ARRAY_SIZE(tests); i++) {
> > +               if (tests[i].run) {             // 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_TASKS_RCU_GENERIC */
> >  static inline void rcu_tasks_bootup_oddness(void) {}
> > -- 
> > 2.20.1
> 
> Again, much improved!
> 
See below the v3 version. I hope i fixed all comments :)