[PATCH tip/core/rcu 16/19] scftorture: Block scftorture_invoker() kthreads for offline CPUs

paulmck
2020-08-31T18:08:18Z

Currently, CPU-hotplug operations might result in all but two
of (say) 100 CPUs being offline, which in turn might result in
false-positive diagnostics due to overload. This commit therefore
causes scftorture_invoker() kthreads for offline CPUs to loop blocking
for 200 milliseconds at a time, thus continuously adjusting the number
of threads to match the number of online CPUs.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/scftorture.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/kernel/scftorture.c b/kernel/scftorture.c
index d9c01c7..04d3a42 100644
--- a/kernel/scftorture.c
+++ b/kernel/scftorture.c
@@ -381,11 +381,14 @@ static void scftorture_invoke_one(struct scf_statistics *scfp, struct torture_ra
// smp_call_function() family of functions.
static int scftorture_invoker(void *arg)
{
+ int cpu;
DEFINE_TORTURE_RANDOM(rand);
struct scf_statistics *scfp = (struct scf_statistics *)arg;
+ bool was_offline = false;

VERBOSE_SCFTORTOUT("scftorture_invoker %d: task started", scfp->cpu);
- set_cpus_allowed_ptr(current, cpumask_of(scfp->cpu % nr_cpu_ids));
+ cpu = scfp->cpu % nr_cpu_ids;
+ set_cpus_allowed_ptr(current, cpumask_of(cpu));
set_user_nice(current, MAX_NICE);
if (holdoff)
schedule_timeout_interruptible(holdoff * HZ);
@@ -408,6 +411,14 @@ static int scftorture_invoker(void *arg)

do {
scftorture_invoke_one(scfp, &rand);
+ while (cpu_is_offline(cpu) && !torture_must_stop()) {
+ schedule_timeout_interruptible(HZ / 5);
+ was_offline = true;
+ }
+ if (was_offline) {
+ set_cpus_allowed_ptr(current, cpumask_of(cpu));
+ was_offline = false;
+ }
} while (!torture_must_stop());

VERBOSE_SCFTORTOUT("scftorture_invoker %d ended", scfp->cpu);
--
2.9.5