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>

1 files changed, 11 insertions, 28 deletions

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;
 }