rcu: add priority-inversion testing to rcutorture

Add an optional test to force long-term preemption of RCU read-side
critical sections, controlled by new test_boost, test_boost_interval,
and test_boost_duration module parameters.  This is to be used to
test RCU priority boosting.

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

diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
index 9d8e8fb..89613f9 100644 (file)
--- a/kernel/rcutorture.c
+++ b/kernel/rcutorture.c
@@ -47,6 +47,7 @@
 #include <linux/srcu.h>
 #include <linux/slab.h>
 #include <asm/byteorder.h>
+#include <linux/sched.h>
 
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Paul E. McKenney <paulmck@us.ibm.com> and "
@@ -64,6 +65,9 @@ static int irqreader = 1;     /* RCU readers from irq (timers). */
 static int fqs_duration = 0;   /* Duration of bursts (us), 0 to disable. */
 static int fqs_holdoff = 0;    /* Hold time within burst (us). */
 static int fqs_stutter = 3;    /* Wait time between bursts (s). */
+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. */
+static int test_boost_duration = 4; /* Duration of each boost test, seconds. */
 static char *torture_type = "rcu"; /* What RCU implementation to torture. */
 
 module_param(nreaders, int, 0444);
@@ -88,6 +92,12 @@ module_param(fqs_holdoff, int, 0444);
 MODULE_PARM_DESC(fqs_holdoff, "Holdoff time within fqs bursts (us)");
 module_param(fqs_stutter, int, 0444);
 MODULE_PARM_DESC(fqs_stutter, "Wait time between fqs bursts (s)");
+module_param(test_boost, int, 0444);
+MODULE_PARM_DESC(test_boost, "Test RCU prio boost: 0=no, 1=maybe, 2=yes.");
+module_param(test_boost_interval, int, 0444);
+MODULE_PARM_DESC(test_boost_interval, "Interval between boost tests, seconds.");
+module_param(test_boost_duration, int, 0444);
+MODULE_PARM_DESC(test_boost_duration, "Duration of each boost test, seconds.");
 module_param(torture_type, charp, 0444);
 MODULE_PARM_DESC(torture_type, "Type of RCU to torture (rcu, rcu_bh, srcu)");
 
@@ -109,6 +119,7 @@ static struct task_struct *stats_task;
 static struct task_struct *shuffler_task;
 static struct task_struct *stutter_task;
 static struct task_struct *fqs_task;
+static struct task_struct *boost_tasks[NR_CPUS];
 
 #define RCU_TORTURE_PIPE_LEN 10
 
@@ -134,6 +145,12 @@ static atomic_t n_rcu_torture_alloc_fail;
 static atomic_t n_rcu_torture_free;
 static atomic_t n_rcu_torture_mberror;
 static atomic_t n_rcu_torture_error;
+static long n_rcu_torture_boost_ktrerror;
+static long n_rcu_torture_boost_rterror;
+static long n_rcu_torture_boost_allocerror;
+static long n_rcu_torture_boost_afferror;
+static long n_rcu_torture_boost_failure;
+static long n_rcu_torture_boosts;
 static long n_rcu_torture_timers;
 static struct list_head rcu_torture_removed;
 static cpumask_var_t shuffle_tmp_mask;
@@ -147,6 +164,16 @@ static int stutter_pause_test;
 #endif
 int rcutorture_runnable = RCUTORTURE_RUNNABLE_INIT;
 
+#ifdef CONFIG_RCU_BOOST
+#define rcu_can_boost() 1
+#else /* #ifdef CONFIG_RCU_BOOST */
+#define rcu_can_boost() 0
+#endif /* #else #ifdef CONFIG_RCU_BOOST */
+
+static unsigned long boost_starttime;  /* jiffies of next boost test start. */
+DEFINE_MUTEX(boost_mutex);             /* protect setting boost_starttime */
+                                       /*  and boost task create/destroy. */
+
 /* Mediate rmmod and system shutdown.  Concurrent rmmod & shutdown illegal! */
 
 #define FULLSTOP_DONTSTOP 0    /* Normal operation. */
@@ -277,6 +304,7 @@ struct rcu_torture_ops {
        void (*fqs)(void);
        int (*stats)(char *page);
        int irq_capable;
+       int can_boost;
        char *name;
 };
 
@@ -366,6 +394,7 @@ static struct rcu_torture_ops rcu_ops = {
        .fqs            = rcu_force_quiescent_state,
        .stats          = NULL,
        .irq_capable    = 1,
+       .can_boost      = rcu_can_boost(),
        .name           = "rcu"
 };
 
@@ -408,6 +437,7 @@ static struct rcu_torture_ops rcu_sync_ops = {
        .fqs            = rcu_force_quiescent_state,
        .stats          = NULL,
        .irq_capable    = 1,
+       .can_boost      = rcu_can_boost(),
        .name           = "rcu_sync"
 };
 
@@ -424,6 +454,7 @@ static struct rcu_torture_ops rcu_expedited_ops = {
        .fqs            = rcu_force_quiescent_state,
        .stats          = NULL,
        .irq_capable    = 1,
+       .can_boost      = rcu_can_boost(),
        .name           = "rcu_expedited"
 };
 
@@ -683,6 +714,110 @@ static struct rcu_torture_ops sched_expedited_ops = {
        .name           = "sched_expedited"
 };
 
+/*
+ * RCU torture priority-boost testing.  Runs one real-time thread per
+ * CPU for moderate bursts, repeatedly registering RCU callbacks and
+ * spinning waiting for them to be invoked.  If a given callback takes
+ * too long to be invoked, we assume that priority inversion has occurred.
+ */
+
+struct rcu_boost_inflight {
+       struct rcu_head rcu;
+       int inflight;
+};
+
+static void rcu_torture_boost_cb(struct rcu_head *head)
+{
+       struct rcu_boost_inflight *rbip =
+               container_of(head, struct rcu_boost_inflight, rcu);
+
+       smp_mb(); /* Ensure RCU-core accesses precede clearing ->inflight */
+       rbip->inflight = 0;
+}
+
+static int rcu_torture_boost(void *arg)
+{
+       unsigned long call_rcu_time;
+       unsigned long endtime;
+       unsigned long oldstarttime;
+       struct rcu_boost_inflight rbi = { .inflight = 0 };
+       struct sched_param sp;
+
+       VERBOSE_PRINTK_STRING("rcu_torture_boost started");
+
+       /* Set real-time priority. */
+       sp.sched_priority = 1;
+       if (sched_setscheduler(current, SCHED_FIFO, &sp) < 0) {
+               VERBOSE_PRINTK_STRING("rcu_torture_boost RT prio failed!");
+               n_rcu_torture_boost_rterror++;
+       }
+
+       /* Each pass through the following loop does one boost-test cycle. */
+       do {
+               /* Wait for the next test interval. */
+               oldstarttime = boost_starttime;
+               while (jiffies - oldstarttime > ULONG_MAX / 2) {
+                       schedule_timeout_uninterruptible(1);
+                       rcu_stutter_wait("rcu_torture_boost");
+                       if (kthread_should_stop() ||
+                           fullstop != FULLSTOP_DONTSTOP)
+                               goto checkwait;
+               }
+
+               /* Do one boost-test interval. */
+               endtime = oldstarttime + test_boost_duration * HZ;
+               call_rcu_time = jiffies;
+               while (jiffies - endtime > ULONG_MAX / 2) {
+                       /* If we don't have a callback in flight, post one. */
+                       if (!rbi.inflight) {
+                               smp_mb(); /* RCU core before ->inflight = 1. */
+                               rbi.inflight = 1;
+                               call_rcu(&rbi.rcu, rcu_torture_boost_cb);
+                               if (jiffies - call_rcu_time >
+                                        test_boost_duration * HZ - HZ / 2) {
+                                       VERBOSE_PRINTK_STRING("rcu_torture_boost boosting failed");
+                                       n_rcu_torture_boost_failure++;
+                               }
+                               call_rcu_time = jiffies;
+                       }
+                       cond_resched();
+                       rcu_stutter_wait("rcu_torture_boost");
+                       if (kthread_should_stop() ||
+                           fullstop != FULLSTOP_DONTSTOP)
+                               goto checkwait;
+               }
+
+               /*
+                * Set the start time of the next test interval.
+                * Yes, this is vulnerable to long delays, but such
+                * delays simply cause a false negative for the next
+                * interval.  Besides, we are running at RT priority,
+                * so delays should be relatively rare.
+                */
+               while (oldstarttime == boost_starttime) {
+                       if (mutex_trylock(&boost_mutex)) {
+                               boost_starttime = jiffies +
+                                                 test_boost_interval * HZ;
+                               n_rcu_torture_boosts++;
+                               mutex_unlock(&boost_mutex);
+                               break;
+                       }
+                       schedule_timeout_uninterruptible(1);
+               }
+
+               /* Go do the stutter. */
+checkwait:     rcu_stutter_wait("rcu_torture_boost");
+       } while (!kthread_should_stop() && fullstop  == FULLSTOP_DONTSTOP);
+
+       /* Clean up and exit. */
+       VERBOSE_PRINTK_STRING("rcu_torture_boost task stopping");
+       rcutorture_shutdown_absorb("rcu_torture_boost");
+       while (!kthread_should_stop() || rbi.inflight)
+               schedule_timeout_uninterruptible(1);
+       smp_mb(); /* order accesses to ->inflight before stack-frame death. */
+       return 0;
+}
+
 /*
  * RCU torture force-quiescent-state kthread.  Repeatedly induces
  * bursts of calls to force_quiescent_state(), increasing the probability
@@ -933,7 +1068,8 @@ rcu_torture_printk(char *page)
        cnt += sprintf(&page[cnt], "%s%s ", torture_type, TORTURE_FLAG);
        cnt += sprintf(&page[cnt],
                       "rtc: %p ver: %ld tfle: %d rta: %d rtaf: %d rtf: %d "
-                      "rtmbe: %d nt: %ld",
+                      "rtmbe: %d rtbke: %ld rtbre: %ld rtbae: %ld rtbafe: %ld "
+                      "rtbf: %ld rtb: %ld nt: %ld",
                       rcu_torture_current,
                       rcu_torture_current_version,
                       list_empty(&rcu_torture_freelist),
@@ -941,8 +1077,19 @@ rcu_torture_printk(char *page)
                       atomic_read(&n_rcu_torture_alloc_fail),
                       atomic_read(&n_rcu_torture_free),
                       atomic_read(&n_rcu_torture_mberror),
+                      n_rcu_torture_boost_ktrerror,
+                      n_rcu_torture_boost_rterror,
+                      n_rcu_torture_boost_allocerror,
+                      n_rcu_torture_boost_afferror,
+                      n_rcu_torture_boost_failure,
+                      n_rcu_torture_boosts,
                       n_rcu_torture_timers);
-       if (atomic_read(&n_rcu_torture_mberror) != 0)
+       if (atomic_read(&n_rcu_torture_mberror) != 0 ||
+           n_rcu_torture_boost_ktrerror != 0 ||
+           n_rcu_torture_boost_rterror != 0 ||
+           n_rcu_torture_boost_allocerror != 0 ||
+           n_rcu_torture_boost_afferror != 0 ||
+           n_rcu_torture_boost_failure != 0)
                cnt += sprintf(&page[cnt], " !!!");
        cnt += sprintf(&page[cnt], "\n%s%s ", torture_type, TORTURE_FLAG);
        if (i > 1) {
@@ -1094,22 +1241,91 @@ rcu_torture_stutter(void *arg)
 }
 
 static inline void
-rcu_torture_print_module_parms(char *tag)
+rcu_torture_print_module_parms(struct rcu_torture_ops *cur_ops, char *tag)
 {
        printk(KERN_ALERT "%s" TORTURE_FLAG
                "--- %s: nreaders=%d nfakewriters=%d "
                "stat_interval=%d verbose=%d test_no_idle_hz=%d "
                "shuffle_interval=%d stutter=%d irqreader=%d "
-               "fqs_duration=%d fqs_holdoff=%d fqs_stutter=%d\n",
+               "fqs_duration=%d fqs_holdoff=%d fqs_stutter=%d "
+               "test_boost=%d/%d test_boost_interval=%d "
+               "test_boost_duration=%d\n",
                torture_type, tag, nrealreaders, nfakewriters,
                stat_interval, verbose, test_no_idle_hz, shuffle_interval,
-               stutter, irqreader, fqs_duration, fqs_holdoff, fqs_stutter);
+               stutter, irqreader, fqs_duration, fqs_holdoff, fqs_stutter,
+               test_boost, cur_ops->can_boost,
+               test_boost_interval, test_boost_duration);
 }
 
-static struct notifier_block rcutorture_nb = {
+static struct notifier_block rcutorture_shutdown_nb = {
        .notifier_call = rcutorture_shutdown_notify,
 };
 
+static void rcutorture_booster_cleanup(int cpu)
+{
+       struct task_struct *t;
+
+       if (boost_tasks[cpu] == NULL)
+               return;
+       mutex_lock(&boost_mutex);
+       VERBOSE_PRINTK_STRING("Stopping rcu_torture_boost task");
+       t = boost_tasks[cpu];
+       boost_tasks[cpu] = NULL;
+       mutex_unlock(&boost_mutex);
+
+       /* This must be outside of the mutex, otherwise deadlock! */
+       kthread_stop(t);
+}
+
+static int rcutorture_booster_init(int cpu)
+{
+       int retval;
+
+       if (boost_tasks[cpu] != NULL)
+               return 0;  /* Already created, nothing more to do. */
+
+       /* Don't allow time recalculation while creating a new task. */
+       mutex_lock(&boost_mutex);
+       VERBOSE_PRINTK_STRING("Creating rcu_torture_boost task");
+       boost_tasks[cpu] = kthread_create(rcu_torture_boost, NULL,
+                                         "rcu_torture_boost");
+       if (IS_ERR(boost_tasks[cpu])) {
+               retval = PTR_ERR(boost_tasks[cpu]);
+               VERBOSE_PRINTK_STRING("rcu_torture_boost task create failed");
+               n_rcu_torture_boost_ktrerror++;
+               boost_tasks[cpu] = NULL;
+               mutex_unlock(&boost_mutex);
+               return retval;
+       }
+       kthread_bind(boost_tasks[cpu], cpu);
+       wake_up_process(boost_tasks[cpu]);
+       mutex_unlock(&boost_mutex);
+       return 0;
+}
+
+static int rcutorture_cpu_notify(struct notifier_block *self,
+                                unsigned long action, void *hcpu)
+{
+       long cpu = (long)hcpu;
+
+       switch (action) {
+       case CPU_ONLINE:
+       case CPU_DOWN_FAILED:
+               (void)rcutorture_booster_init(cpu);
+               break;
+       case CPU_DOWN_PREPARE:
+               rcutorture_booster_cleanup(cpu);
+               break;
+       default:
+               break;
+       }
+       return NOTIFY_OK;
+}
+
+static struct notifier_block rcutorture_cpu_nb = {
+       .notifier_call = rcutorture_cpu_notify,
+};
+
 static void
 rcu_torture_cleanup(void)
 {
@@ -1127,7 +1343,7 @@ rcu_torture_cleanup(void)
        }
        fullstop = FULLSTOP_RMMOD;
        mutex_unlock(&fullstop_mutex);
-       unregister_reboot_notifier(&rcutorture_nb);
+       unregister_reboot_notifier(&rcutorture_shutdown_nb);
        if (stutter_task) {
                VERBOSE_PRINTK_STRING("Stopping rcu_torture_stutter task");
                kthread_stop(stutter_task);
@@ -1184,6 +1400,12 @@ rcu_torture_cleanup(void)
                kthread_stop(fqs_task);
        }
        fqs_task = NULL;
+       if ((test_boost == 1 && cur_ops->can_boost) ||
+           test_boost == 2) {
+               unregister_cpu_notifier(&rcutorture_cpu_nb);
+               for_each_possible_cpu(i)
+                       rcutorture_booster_cleanup(i);
+       }
 
        /* Wait for all RCU callbacks to fire.  */
 
@@ -1195,9 +1417,9 @@ rcu_torture_cleanup(void)
        if (cur_ops->cleanup)
                cur_ops->cleanup();
        if (atomic_read(&n_rcu_torture_error))
-               rcu_torture_print_module_parms("End of test: FAILURE");
+               rcu_torture_print_module_parms(cur_ops, "End of test: FAILURE");
        else
-               rcu_torture_print_module_parms("End of test: SUCCESS");
+               rcu_torture_print_module_parms(cur_ops, "End of test: SUCCESS");
 }
 
 static int __init
@@ -1242,7 +1464,7 @@ rcu_torture_init(void)
                nrealreaders = nreaders;
        else
                nrealreaders = 2 * num_online_cpus();
-       rcu_torture_print_module_parms("Start of test");
+       rcu_torture_print_module_parms(cur_ops, "Start of test");
        fullstop = FULLSTOP_DONTSTOP;
 
        /* Set up the freelist. */
@@ -1263,6 +1485,12 @@ rcu_torture_init(void)
        atomic_set(&n_rcu_torture_free, 0);
        atomic_set(&n_rcu_torture_mberror, 0);
        atomic_set(&n_rcu_torture_error, 0);
+       n_rcu_torture_boost_ktrerror = 0;
+       n_rcu_torture_boost_rterror = 0;
+       n_rcu_torture_boost_allocerror = 0;
+       n_rcu_torture_boost_afferror = 0;
+       n_rcu_torture_boost_failure = 0;
+       n_rcu_torture_boosts = 0;
        for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++)
                atomic_set(&rcu_torture_wcount[i], 0);
        for_each_possible_cpu(cpu) {
@@ -1376,7 +1604,27 @@ rcu_torture_init(void)
                        goto unwind;
                }
        }
-       register_reboot_notifier(&rcutorture_nb);
+       if (test_boost_interval < 1)
+               test_boost_interval = 1;
+       if (test_boost_duration < 2)
+               test_boost_duration = 2;
+       if ((test_boost == 1 && cur_ops->can_boost) ||
+           test_boost == 2) {
+               int retval;
+
+               boost_starttime = jiffies + test_boost_interval * HZ;
+               register_cpu_notifier(&rcutorture_cpu_nb);
+               for_each_possible_cpu(i) {
+                       if (cpu_is_offline(i))
+                               continue;  /* Heuristic: CPU can go offline. */
+                       retval = rcutorture_booster_init(i);
+                       if (retval < 0) {
+                               firsterr = retval;
+                               goto unwind;
+                       }
+               }
+       }
+       register_reboot_notifier(&rcutorture_shutdown_nb);
        mutex_unlock(&fullstop_mutex);
        return 0;