rcutorture: Permit holding off CPU-hotplug operations during boot

When rcutorture is started automatically at boot time, it might well
also start CPU-hotplug operations at that time, which might not be
desirable.  This commit therefore adds an rcutorture parameter that
allows CPU-hotplug operations to be held off for the specified number
of seconds after the start of boot.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/Documentation/RCU/torture.txt b/Documentation/RCU/torture.txt
index d67068d..01a809b 100644 (file)
--- a/Documentation/RCU/torture.txt
+++ b/Documentation/RCU/torture.txt
@@ -69,6 +69,13 @@ onoff_interval
                CPU-hotplug operations regardless of what value is
                specified for onoff_interval.
 
+onoff_holdoff  The number of seconds to wait until starting CPU-hotplug
+               operations.  This would normally only be used when
+               rcutorture was built into the kernel and started
+               automatically at boot time, in which case it is useful
+               in order to avoid confusing boot-time code with CPUs
+               coming and going.
+
 shuffle_interval
                The number of seconds to keep the test threads affinitied
                to a particular subset of the CPUs, defaults to 3 seconds.
@@ -277,5 +284,7 @@ The following script may be used to torture RCU:
 
 The output can be manually inspected for the error flag of "!!!".
 One could of course create a more elaborate script that automatically
-checked for such errors.  The "rmmod" command forces a "SUCCESS" or
-"FAILURE" indication to be printk()ed.
+checked for such errors.  The "rmmod" command forces a "SUCCESS",
+"FAILURE", or "RCU_HOTPLUG" indication to be printk()ed.  The first
+two are self-explanatory, while the last indicates that while there
+were no RCU failures, CPU-hotplug problems were detected.

diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
index a52b321..2914caf 100644 (file)
--- a/kernel/rcutorture.c
+++ b/kernel/rcutorture.c
@@ -65,6 +65,7 @@ static int fqs_duration;      /* Duration of bursts (us), 0 to disable. */
 static int fqs_holdoff;                /* Hold time within burst (us). */
 static int fqs_stutter = 3;    /* Wait time between bursts (s). */
 static int onoff_interval;     /* Wait time between CPU hotplugs, 0=disable. */
+static int onoff_holdoff;      /* Seconds after boot before CPU hotplugs. */
 static int shutdown_secs;      /* Shutdown time (s).  <=0 for no shutdown. */
 static int test_boost = 1;     /* Test RCU prio boost: 0=no, 1=maybe, 2=yes. */
 static int test_boost_interval = 7; /* Interval between boost tests, seconds. */
@@ -95,6 +96,8 @@ module_param(fqs_stutter, int, 0444);
 MODULE_PARM_DESC(fqs_stutter, "Wait time between fqs bursts (s)");
 module_param(onoff_interval, int, 0444);
 MODULE_PARM_DESC(onoff_interval, "Time between CPU hotplugs (s), 0=disable");
+module_param(onoff_holdoff, int, 0444);
+MODULE_PARM_DESC(onoff_holdoff, "Time after boot before CPU hotplugs (s)");
 module_param(shutdown_secs, int, 0444);
 MODULE_PARM_DESC(shutdown_secs, "Shutdown time (s), zero to disable.");
 module_param(test_boost, int, 0444);
@@ -1300,13 +1303,13 @@ rcu_torture_print_module_parms(struct rcu_torture_ops *cur_ops, char *tag)
                "fqs_duration=%d fqs_holdoff=%d fqs_stutter=%d "
                "test_boost=%d/%d test_boost_interval=%d "
                "test_boost_duration=%d shutdown_secs=%d "
-               "onoff_interval=%d\n",
+               "onoff_interval=%d onoff_holdoff=%d\n",
                torture_type, tag, nrealreaders, nfakewriters,
                stat_interval, verbose, test_no_idle_hz, shuffle_interval,
                stutter, irqreader, fqs_duration, fqs_holdoff, fqs_stutter,
                test_boost, cur_ops->can_boost,
                test_boost_interval, test_boost_duration, shutdown_secs,
-               onoff_interval);
+               onoff_interval, onoff_holdoff);
 }
 
 static struct notifier_block rcutorture_shutdown_nb = {
@@ -1410,6 +1413,11 @@ rcu_torture_onoff(void *arg)
        for_each_online_cpu(cpu)
                maxcpu = cpu;
        WARN_ON(maxcpu < 0);
+       if (onoff_holdoff > 0) {
+               VERBOSE_PRINTK_STRING("rcu_torture_onoff begin holdoff");
+               schedule_timeout_interruptible(onoff_holdoff * HZ);
+               VERBOSE_PRINTK_STRING("rcu_torture_onoff end holdoff");
+       }
        while (!kthread_should_stop()) {
                cpu = (rcu_random(&rand) >> 4) % (maxcpu + 1);
                if (cpu_online(cpu) && cpu_is_hotpluggable(cpu)) {