[PATCH tip/core/rcu 0/4] Lock torture-test updates for v5.7

[PATCH tip/core/rcu 0/4] Lock torture-test updates for v5.7

[Paul E. McKenney]

Hello!

This series provides locktorture updates.

1.	Print ratio of acquisitions, not failures.

2.	Allow CPU-hotplug to be disabled via --bootargs.

3.	Use private random-number generators.

4.	Forgive apparent unfairness if CPU hotplug.

							Thanx, Paul

------------------------------------------------------------------------

 kernel/locking/locktorture.c                        |   15 ++++++++-------
 tools/testing/selftests/rcutorture/bin/functions.sh |    2 +-
 2 files changed, 9 insertions(+), 8 deletions(-)

[PATCH tip/core/rcu 1/4] locktorture: Print ratio of acquisitions, not failures

[paulmck]

From: "Paul E. McKenney" <paulmck@kernel.org>

The __torture_print_stats() function in locktorture.c carefully
initializes local variable "min" to statp[0].n_lock_acquired, but
then compares it to statp[i].n_lock_fail.  Given that the .n_lock_fail
field should normally be zero, and given the initialization, it seems
reasonable to display the maximum and minimum number acquisitions
instead of miscomputing the maximum and minimum number of failures.
This commit therefore switches from failures to acquisitions.

And this turns out to be not only a day-zero bug, but entirely my
own fault.  I hate it when that happens!

Fixes: 0af3fe1efa53 ("locktorture: Add a lock-torture kernel module")
Reported-by: Will Deacon <will@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Acked-by: Will Deacon <will@kernel.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Peter Zijlstra <peterz@infradead.org>
---
 kernel/locking/locktorture.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
index 99475a6..687c1d8 100644
--- a/kernel/locking/locktorture.c
+++ b/kernel/locking/locktorture.c
@@ -696,10 +696,10 @@ static void __torture_print_stats(char *page,
 		if (statp[i].n_lock_fail)
 			fail = true;
 		sum += statp[i].n_lock_acquired;
-		if (max < statp[i].n_lock_fail)
-			max = statp[i].n_lock_fail;
-		if (min > statp[i].n_lock_fail)
-			min = statp[i].n_lock_fail;
+		if (max < statp[i].n_lock_acquired)
+			max = statp[i].n_lock_acquired;
+		if (min > statp[i].n_lock_acquired)
+			min = statp[i].n_lock_acquired;
 	}
 	page += sprintf(page,
 			"%s:  Total: %lld  Max/Min: %ld/%ld %s  Fail: %d %s\n",
-- 
2.9.5

[PATCH tip/core/rcu 2/4] locktorture: Allow CPU-hotplug to be disabled via --bootargs

[paulmck]

From: "Paul E. McKenney" <paulmck@kernel.org>

The bootparam_hotplug_cpu() bash function was checking for CPU-hotplug
kernel-boot parameters from --bootargs, but that check was specific to
rcutorture ("rcutorture\.onoff_").  This commit therefore makes this
check also work for locktorture ("torture\.onoff_").

Note that rcuperf does not do CPU-hotplug operations, so it is not
necessary to make a similar change for rcuperf.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 tools/testing/selftests/rcutorture/bin/functions.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/rcutorture/bin/functions.sh b/tools/testing/selftests/rcutorture/bin/functions.sh
index c3a49fb..1281022 100644
--- a/tools/testing/selftests/rcutorture/bin/functions.sh
+++ b/tools/testing/selftests/rcutorture/bin/functions.sh
@@ -12,7 +12,7 @@
 # Returns 1 if the specified boot-parameter string tells rcutorture to
 # test CPU-hotplug operations.
 bootparam_hotplug_cpu () {
-	echo "$1" | grep -q "rcutorture\.onoff_"
+	echo "$1" | grep -q "torture\.onoff_"
 }
 
 # checkarg --argname argtype $# arg mustmatch cannotmatch
-- 
2.9.5

[PATCH tip/core/rcu 3/4] locktorture: Use private random-number generators

[paulmck]

From: "Paul E. McKenney" <paulmck@kernel.org>

Both lock_torture_writer() and lock_torture_reader() use the "static"
keyword on their DEFINE_TORTURE_RANDOM(rand) declarations, which means
that a single instance of a random-number generator are shared among all
the writers and another is shared among all the readers.  Unfortunately,
this random-number generator was not designed for concurrent access.
This commit therefore removes both "static" keywords so that each reader
and each writer gets its own random-number generator.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/locking/locktorture.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
index 687c1d8..5baf904 100644
--- a/kernel/locking/locktorture.c
+++ b/kernel/locking/locktorture.c
@@ -618,7 +618,7 @@ static struct lock_torture_ops percpu_rwsem_lock_ops = {
 static int lock_torture_writer(void *arg)
 {
 	struct lock_stress_stats *lwsp = arg;
-	static DEFINE_TORTURE_RANDOM(rand);
+	DEFINE_TORTURE_RANDOM(rand);
 
 	VERBOSE_TOROUT_STRING("lock_torture_writer task started");
 	set_user_nice(current, MAX_NICE);
@@ -655,7 +655,7 @@ static int lock_torture_writer(void *arg)
 static int lock_torture_reader(void *arg)
 {
 	struct lock_stress_stats *lrsp = arg;
-	static DEFINE_TORTURE_RANDOM(rand);
+	DEFINE_TORTURE_RANDOM(rand);
 
 	VERBOSE_TOROUT_STRING("lock_torture_reader task started");
 	set_user_nice(current, MAX_NICE);
-- 
2.9.5

[PATCH tip/core/rcu 4/4] locktorture: Forgive apparent unfairness if CPU hotplug

[paulmck]

From: "Paul E. McKenney" <paulmck@kernel.org>

If CPU hotplug testing is enabled, a lock might appear to be maximally
unfair just because one of the CPUs was offline almost all the time.
This commit therefore forgives unfairness if CPU hotplug testing was
enabled.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/locking/locktorture.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
index 5baf904..5efbfc6 100644
--- a/kernel/locking/locktorture.c
+++ b/kernel/locking/locktorture.c
@@ -704,7 +704,8 @@ static void __torture_print_stats(char *page,
 	page += sprintf(page,
 			"%s:  Total: %lld  Max/Min: %ld/%ld %s  Fail: %d %s\n",
 			write ? "Writes" : "Reads ",
-			sum, max, min, max / 2 > min ? "???" : "",
+			sum, max, min,
+			!onoff_interval && max / 2 > min ? "???" : "",
 			fail, fail ? "!!!" : "");
 	if (fail)
 		atomic_inc(&cxt.n_lock_torture_errors);
-- 
2.9.5