scftorture: Block scftorture_invoker() kthreads for offline CPUs

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>

diff --git a/kernel/scftorture.c b/kernel/scftorture.c
index d9c01c7..04d3a42 100644 (file)
--- 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);