rcutorture: Fix rcutorture shutdown races

Not all of the rcutorture kthreads waited for kthread_should_stop()
before returning from their top-level functions, and none of them
used torture_shutdown_absorb() properly.  These problems can result in
segfaults and hangs at shutdown time, and some recent changes perturbed
timing sufficiently to make them much more probable.  This commit
therefore creates a torture_kthread_stopping() function that does the
proper kthread shutdown dance in one centralized location.

Accommodate this grouping by making VERBOSE_TOROUT_STRING() capable of
taking a non-const string as its argument, which allows the new
torture_kthread_stopping() to pass its "title" argument directly to
the updated version of VERBOSE_TOROUT_STRING().

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

3 files changed, 35 insertions, 33 deletions

diff --git a/include/linux/torture.h b/include/linux/torture.h
index c79c41d543ef..2ea11094daf6 100644
--- a/include/linux/torture.h
+++ b/include/linux/torture.h
@@ -45,7 +45,7 @@
 #define TOROUT_STRING(s) \
         pr_alert("%s" TORTURE_FLAG s "\n", torture_type)
 #define VERBOSE_TOROUT_STRING(s) \
-        do { if (verbose) pr_alert("%s" TORTURE_FLAG s "\n", torture_type); } while (0)
+        do { if (verbose) pr_alert("%s" TORTURE_FLAG " %s\n", torture_type, s); } while (0)
 #define VERBOSE_TOROUT_ERRSTRING(s) \
         do { if (verbose) pr_alert("%s" TORTURE_FLAG "!!! " s "\n", torture_type); } while (0)
 
@@ -88,5 +88,6 @@ void torture_init_end(void);
 bool torture_cleanup(void);
 bool torture_must_stop(void);
 bool torture_must_stop_irq(void);
+void torture_kthread_stopping(char *title);
 
 #endif /* __LINUX_TORTURE_H */
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 6e9ba51b23b9..bcaafd6cf633 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -602,12 +602,13 @@ checkwait:	stutter_wait("rcu_torture_boost");
         } while (!torture_must_stop());
 
         /* Clean up and exit. */
-        VERBOSE_TOROUT_STRING("rcu_torture_boost task stopping");
-        torture_shutdown_absorb("rcu_torture_boost");
-        while (!kthread_should_stop() || rbi.inflight)
+        while (!kthread_should_stop() || rbi.inflight) {
+                torture_shutdown_absorb("rcu_torture_boost");
                 schedule_timeout_uninterruptible(1);
+        }
         smp_mb(); /* order accesses to ->inflight before stack-frame death. */
         destroy_rcu_head_on_stack(&rbi.rcu);
+        torture_kthread_stopping("rcu_torture_boost");
         return 0;
 }
 
@@ -638,10 +639,7 @@ rcu_torture_fqs(void *arg)
                 }
                 stutter_wait("rcu_torture_fqs");
         } while (!torture_must_stop());
-        VERBOSE_TOROUT_STRING("rcu_torture_fqs task stopping");
-        torture_shutdown_absorb("rcu_torture_fqs");
-        while (!kthread_should_stop())
-                schedule_timeout_uninterruptible(1);
+        torture_kthread_stopping("rcu_torture_fqs");
         return 0;
 }
 
@@ -710,10 +708,7 @@ rcu_torture_writer(void *arg)
                 rcutorture_record_progress(++rcu_torture_current_version);
                 stutter_wait("rcu_torture_writer");
         } while (!torture_must_stop());
-        VERBOSE_TOROUT_STRING("rcu_torture_writer task stopping");
-        torture_shutdown_absorb("rcu_torture_writer");
-        while (!kthread_should_stop())
-                schedule_timeout_uninterruptible(1);
+        torture_kthread_stopping("rcu_torture_writer");
         return 0;
 }
 
@@ -748,10 +743,7 @@ rcu_torture_fakewriter(void *arg)
                 stutter_wait("rcu_torture_fakewriter");
         } while (!torture_must_stop());
 
-        VERBOSE_TOROUT_STRING("rcu_torture_fakewriter task stopping");
-        torture_shutdown_absorb("rcu_torture_fakewriter");
-        while (!kthread_should_stop())
-                schedule_timeout_uninterruptible(1);
+        torture_kthread_stopping("rcu_torture_fakewriter");
         return 0;
 }
 
@@ -892,12 +884,9 @@ rcu_torture_reader(void *arg)
                 schedule();
                 stutter_wait("rcu_torture_reader");
         } while (!torture_must_stop());
-        VERBOSE_TOROUT_STRING("rcu_torture_reader task stopping");
-        torture_shutdown_absorb("rcu_torture_reader");
         if (irqreader && cur_ops->irq_capable)
                 del_timer_sync(&t);
-        while (!kthread_should_stop())
-                schedule_timeout_uninterruptible(1);
+        torture_kthread_stopping("rcu_torture_reader");
         return 0;
 }
 
@@ -1010,7 +999,7 @@ rcu_torture_stats(void *arg)
                 rcu_torture_stats_print();
                 torture_shutdown_absorb("rcu_torture_stats");
         } while (!torture_must_stop());
-        VERBOSE_TOROUT_STRING("rcu_torture_stats task stopping");
+        torture_kthread_stopping("rcu_torture_stats");
         return 0;
 }
 
@@ -1171,12 +1160,9 @@ static int rcu_torture_barrier_cbs(void *arg)
                 if (atomic_dec_and_test(&barrier_cbs_count))
                         wake_up(&barrier_wq);
         } while (!torture_must_stop());
-        VERBOSE_TOROUT_STRING("rcu_torture_barrier_cbs task stopping");
-        torture_shutdown_absorb("rcu_torture_barrier_cbs");
-        while (!kthread_should_stop())
-                schedule_timeout_interruptible(1);
         cur_ops->cb_barrier();
         destroy_rcu_head_on_stack(&rcu);
+        torture_kthread_stopping("rcu_torture_barrier_cbs");
         return 0;
 }
 
@@ -1207,10 +1193,7 @@ static int rcu_torture_barrier(void *arg)
                 n_barrier_successes++;
                 schedule_timeout_interruptible(HZ / 10);
         } while (!torture_must_stop());
-        VERBOSE_TOROUT_STRING("rcu_torture_barrier task stopping");
-        torture_shutdown_absorb("rcu_torture_barrier");
-        while (!kthread_should_stop())
-                schedule_timeout_interruptible(1);
+        torture_kthread_stopping("rcu_torture_barrier");
         return 0;
 }
 
diff --git a/kernel/torture.c b/kernel/torture.c
index 5e2838f902f9..330576660cf4 100644
--- a/kernel/torture.c
+++ b/kernel/torture.c
@@ -169,7 +169,7 @@ torture_onoff(void *arg)
                 }
                 schedule_timeout_interruptible(onoff_interval);
         }
-        VERBOSE_TOROUT_STRING("torture_onoff task stopping");
+        torture_kthread_stopping("torture_onoff");
         return 0;
 }
 
@@ -370,7 +370,7 @@ static int torture_shuffle(void *arg)
                 torture_shuffle_tasks();
                 torture_shutdown_absorb("torture_shuffle");
         } while (!torture_must_stop());
-        VERBOSE_TOROUT_STRING("torture_shuffle task stopping");
+        torture_kthread_stopping("torture_shuffle");
         return 0;
 }
 
@@ -465,7 +465,7 @@ static int torture_shutdown(void *arg)
                 jiffies_snap = jiffies;
         }
         if (torture_must_stop()) {
-                VERBOSE_TOROUT_STRING("torture_shutdown task stopping");
+                torture_kthread_stopping("torture_shutdown");
                 return 0;
         }
 
@@ -583,7 +583,7 @@ static int torture_stutter(void *arg)
                 ACCESS_ONCE(stutter_pause_test) = 0;
                 torture_shutdown_absorb("torture_stutter");
         } while (!torture_must_stop());
-        VERBOSE_TOROUT_STRING("torture_stutter task stopping");
+        torture_kthread_stopping("torture_stutter");
         return 0;
 }
 
@@ -696,3 +696,21 @@ bool torture_must_stop_irq(void)
         return ACCESS_ONCE(fullstop) != FULLSTOP_DONTSTOP;
 }
 EXPORT_SYMBOL_GPL(torture_must_stop_irq);
+
+/*
+ * Each kthread must wait for kthread_should_stop() before returning from
+ * its top-level function, otherwise segfaults ensue.  This function
+ * prints a "stopping" message and waits for kthread_should_stop(), and
+ * should be called from all torture kthreads immediately prior to
+ * returning.
+ */
+void torture_kthread_stopping(char *title)
+{
+        if (verbose)
+                VERBOSE_TOROUT_STRING(title);
+        while (!kthread_should_stop()) {
+                torture_shutdown_absorb(title);
+                schedule_timeout_uninterruptible(1);
+        }
+}
+EXPORT_SYMBOL_GPL(torture_kthread_stopping);