[tip:core/rcu] rcutorture: Check GP completion at stutter end

["tip-bot for Paul E. McKenney" <tipbot@xxxxxxxxx>]

Commit-ID:  474e59b476b3390ef9f730515439f21640b61623
Gitweb:     https://git.kernel.org/tip/474e59b476b3390ef9f730515439f21640b61623
Author:     Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Tue, 7 Aug 2018 14:34:44 -0700
Committer:  Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Wed, 29 Aug 2018 09:20:48 -0700

rcutorture: Check GP completion at stutter end

The rcu_torture_writer() function invokes stutter_wait() at the end of
each writer pass, which occasionally blocks for an extended time period
in order to ensure that RCU can handle intermittent loads.  But part of
handling a busy period is invoking all the callbacks before the end of
the idle period induced by stutter_wait().

This commit therefore adds a return value to stutter_wait() indicating
whether stutter_wait() actually waited.  In addition, this commit causes
rcu_torture_writer() to test this value and if set, checks that all the
elements of the rcu_tortures[] array have been freed up.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
 include/linux/torture.h | 2 +-
 kernel/rcu/rcutorture.c | 5 ++++-
 kernel/torture.c        | 3 ++-
 3 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/include/linux/torture.h b/include/linux/torture.h
index 61dfd93b6ee4..48fad21109fc 100644
--- a/include/linux/torture.h
+++ b/include/linux/torture.h
@@ -77,7 +77,7 @@ void torture_shutdown_absorb(const char *title);
 int torture_shutdown_init(int ssecs, void (*cleanup)(void));
 
 /* Task stuttering, which forces load/no-load transitions. */
-void stutter_wait(const char *title);
+bool stutter_wait(const char *title);
 int torture_stutter_init(int s);
 
 /* Initialization and cleanup. */
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 7df8142a6a22..ae10ad531993 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1144,7 +1144,10 @@ rcu_torture_writer(void *arg)
 				       !rcu_gp_is_normal();
 		}
 		rcu_torture_writer_state = RTWS_STUTTER;
-		stutter_wait("rcu_torture_writer");
+		if (stutter_wait("rcu_torture_writer"))
+			for (i = 0; i < ARRAY_SIZE(rcu_tortures); i++)
+				if (list_empty(&rcu_tortures[i].rtort_free))
+					WARN_ON_ONCE(1);
 	} while (!torture_must_stop());
 	/* Reset expediting back to unexpedited. */
 	if (expediting > 0)
diff --git a/kernel/torture.c b/kernel/torture.c
index 1ac24a826589..17d91f5fba2a 100644
--- a/kernel/torture.c
+++ b/kernel/torture.c
@@ -573,7 +573,7 @@ static int stutter;
  * Block until the stutter interval ends.  This must be called periodically
  * by all running kthreads that need to be subject to stuttering.
  */
-void stutter_wait(const char *title)
+bool stutter_wait(const char *title)
 {
 	int spt;
 
@@ -590,6 +590,7 @@ void stutter_wait(const char *title)
 		}
 		torture_shutdown_absorb(title);
 	}
+	return !!spt;
 }
 EXPORT_SYMBOL_GPL(stutter_wait);