rcutorture: Fix stutter_wait() return value and freelist checks

The stutter_wait() function is supposed to return true if it actually
waits and false otherwise, but it instead unconditionally returns false.
Which hides a bug in rcu_torture_writer() that fails to account for
the fact that one of the rcu_tortures[] array elements will normally be
referenced by rcu_torture_current, and thus not be on the freelist.

This commit therefore corrects the stutter_wait() return value and adds a
check for rcu_torture_current to rcu_torture_writer()'s check that things
get freed after everything goes quiescent.  In addition, this commit
causes torture_stutter() to give a bit more than one second (instead of
only one jiffy) warning of the end of the stutter interval.  Finally,
this commit disables long-delay readers and aggressive update-side
forward-progress checks while forward-progress testing is in flight.

Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

2 files changed, 25 insertions, 8 deletions

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 7906ba2d9dad..954ac2b98619 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1010,10 +1010,13 @@ rcu_torture_writer(void *arg)
                                        !rcu_gp_is_normal();
                 }
                 rcu_torture_writer_state = RTWS_STUTTER;
-                if (stutter_wait("rcu_torture_writer"))
+                if (stutter_wait("rcu_torture_writer") &&
+                    !READ_ONCE(rcu_fwd_cb_nodelay))
                         for (i = 0; i < ARRAY_SIZE(rcu_tortures); i++)
-                                if (list_empty(&rcu_tortures[i].rtort_free))
-                                        WARN_ON_ONCE(1);
+                                if (list_empty(&rcu_tortures[i].rtort_free) &&
+                                    rcu_access_pointer(rcu_torture_current) !=
+                                    &rcu_tortures[i])
+                                        WARN(1, "%s: rtort_pipe_count: %d\n", __func__, rcu_tortures[i].rtort_pipe_count);
         } while (!torture_must_stop());
         /* Reset expediting back to unexpedited. */
         if (expediting > 0)
@@ -1709,6 +1712,8 @@ static void rcu_torture_fwd_prog_nr(int *tested, int *tested_tries)
         }
 
         /* Tight loop containing cond_resched(). */
+        WRITE_ONCE(rcu_fwd_cb_nodelay, true);
+        cur_ops->sync(); /* Later readers see above write. */
         if  (selfpropcb) {
                 WRITE_ONCE(fcs.stop, 0);
                 cur_ops->call(&fcs.rh, rcu_torture_fwd_prog_cb);
@@ -1747,6 +1752,8 @@ static void rcu_torture_fwd_prog_nr(int *tested, int *tested_tries)
                 WARN_ON(READ_ONCE(fcs.stop) != 2);
                 destroy_rcu_head_on_stack(&fcs.rh);
         }
+        schedule_timeout_uninterruptible(HZ / 10); /* Let kthreads recover. */
+        WRITE_ONCE(rcu_fwd_cb_nodelay, false);
 }
 
 /* Carry out call_rcu() forward-progress testing. */
@@ -1816,7 +1823,6 @@ static void rcu_torture_fwd_prog_cr(void)
         cur_ops->cb_barrier(); /* Wait for callbacks to be invoked. */
         (void)rcu_torture_fwd_prog_cbfree();
 
-        WRITE_ONCE(rcu_fwd_cb_nodelay, false);
         if (!torture_must_stop() && !READ_ONCE(rcu_fwd_emergency_stop)) {
                 WARN_ON(n_max_gps < MIN_FWD_CBS_LAUNDERED);
                 pr_alert("%s Duration %lu barrier: %lu pending %ld n_launders: %ld n_launders_sa: %ld n_max_gps: %ld n_max_cbs: %ld cver %ld gps %ld\n",
@@ -1827,6 +1833,8 @@ static void rcu_torture_fwd_prog_cr(void)
                          n_max_gps, n_max_cbs, cver, gps);
                 rcu_torture_fwd_cb_hist();
         }
+        schedule_timeout_uninterruptible(HZ); /* Let CBs drain. */
+        WRITE_ONCE(rcu_fwd_cb_nodelay, false);
 }
 
 
diff --git a/kernel/torture.c b/kernel/torture.c
index 17b2be9bde12..de0e0ecf88e1 100644
--- a/kernel/torture.c
+++ b/kernel/torture.c
@@ -578,10 +578,12 @@ static int stutter;
 bool stutter_wait(const char *title)
 {
         int spt;
+        bool ret = false;
 
         cond_resched_tasks_rcu_qs();
         spt = READ_ONCE(stutter_pause_test);
         for (; spt; spt = READ_ONCE(stutter_pause_test)) {
+                ret = true;
                 if (spt == 1) {
                         schedule_timeout_interruptible(1);
                 } else if (spt == 2) {
@@ -592,7 +594,7 @@ bool stutter_wait(const char *title)
                 }
                 torture_shutdown_absorb(title);
         }
-        return !!spt;
+        return ret;
 }
 EXPORT_SYMBOL_GPL(stutter_wait);
 
@@ -602,13 +604,20 @@ EXPORT_SYMBOL_GPL(stutter_wait);
  */
 static int torture_stutter(void *arg)
 {
+        int wtime;
+
         VERBOSE_TOROUT_STRING("torture_stutter task started");
         do {
                 if (!torture_must_stop() && stutter > 1) {
-                        WRITE_ONCE(stutter_pause_test, 1);
-                        schedule_timeout_interruptible(stutter - 1);
+                        wtime = stutter;
+                        if (stutter > HZ + 1) {
+                                WRITE_ONCE(stutter_pause_test, 1);
+                                wtime = stutter - HZ - 1;
+                                schedule_timeout_interruptible(wtime);
+                                wtime = HZ + 1;
+                        }
                         WRITE_ONCE(stutter_pause_test, 2);
-                        schedule_timeout_interruptible(1);
+                        schedule_timeout_interruptible(wtime);
                 }
                 WRITE_ONCE(stutter_pause_test, 0);
                 if (!torture_must_stop())