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>

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 7906ba2d9dad91ee680dc93bdd85fb98a67286cb..954ac2b986193d7fb9291b3f3f5df7cf67c6da8d 100644 (file)
--- 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 17b2be9bde12aa22a010788a2143eeedddc3a6c3..de0e0ecf88e1693bbc5a16acf676d187a0c47f5b 100644 (file)
--- 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())