[PATCH 4.7 019/141] rcuperf: Dont treat gp_exp mis-setting as a WARN

From: Greg Kroah-Hartman
Date: Thu Oct 06 2016 - 04:33:43 EST

4.7-stable review patch. If anyone has any objections, please let me know.


From: Boqun Feng <boqun.feng@xxxxxxxxx>

commit af06d4f74a7d2132c805339bfd5ab771b5706f42 upstream.

0day found a boot warning triggered in rcu_perf_writer() on !SMP kernel:

WARN_ON(rcu_gp_is_normal() && gp_exp);

, the root cause of which is trying to measure expedited grace
periods(by setting gp_exp to true by default) when all the grace periods
are normal(TINY RCU only has normal grace periods).

However, such a mis-setting would only result in failing to measure the
performance for a specific kind of grace periods, therefore using a
WARN_ON to check this is a little overkilling. We could handle this
inside rcuperf module via some error messages to tell users about the

Therefore this patch removes the WARN_ON in rcu_perf_writer() and
handles those checkings in rcu_perf_init() with plain if() code.

Moreover, this patch changes the default value of gp_exp to 1) align
with rcutorture tests and 2) make the default setting work for all RCU
implementations by default.

Suggested-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx>
Fixes: http://lkml.kernel.org/r/57411b10.mFvG0+AgcrMXGtcj%fengguang.wu@xxxxxxxxx
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

kernel/rcu/rcuperf.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)

--- a/kernel/rcu/rcuperf.c
+++ b/kernel/rcu/rcuperf.c
@@ -58,7 +58,7 @@ MODULE_AUTHOR("Paul E. McKenney <paulmck
do { if (verbose) pr_alert("%s" PERF_FLAG "!!! %s\n", perf_type, s); } while (0)

-torture_param(bool, gp_exp, true, "Use expedited GP wait primitives");
+torture_param(bool, gp_exp, false, "Use expedited GP wait primitives");
torture_param(int, holdoff, 10, "Holdoff time before test start (s)");
torture_param(int, nreaders, -1, "Number of RCU reader threads");
torture_param(int, nwriters, -1, "Number of RCU updater threads");
@@ -363,8 +363,6 @@ rcu_perf_writer(void *arg)
u64 *wdpp = writer_durations[me];

VERBOSE_PERFOUT_STRING("rcu_perf_writer task started");
- WARN_ON(rcu_gp_is_expedited() && !rcu_gp_is_normal() && !gp_exp);
- WARN_ON(rcu_gp_is_normal() && gp_exp);
set_cpus_allowed_ptr(current, cpumask_of(me % nr_cpu_ids));
sp.sched_priority = 1;
@@ -631,6 +629,16 @@ rcu_perf_init(void)
firsterr = -ENOMEM;
goto unwind;
+ if (rcu_gp_is_expedited() && !rcu_gp_is_normal() && !gp_exp) {
+ VERBOSE_PERFOUT_ERRSTRING("All grace periods expedited, no normal ones to measure!");
+ firsterr = -EINVAL;
+ goto unwind;
+ }
+ if (rcu_gp_is_normal() && gp_exp) {
+ VERBOSE_PERFOUT_ERRSTRING("All grace periods normal, no expedited ones to measure!");
+ firsterr = -EINVAL;
+ goto unwind;
+ }
for (i = 0; i < nrealwriters; i++) {
writer_durations[i] =
kcalloc(MAX_MEAS, sizeof(*writer_durations[i]),