Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull RCU updates from Ingo Molnar:
 "The main RCU changes in this cycle were:

   - Updates to use cond_resched() instead of cond_resched_rcu_qs()
     where feasible (currently everywhere except in kernel/rcu and in
     kernel/torture.c). Also a couple of fixes to avoid sending IPIs to
     offline CPUs.

   - Updates to simplify RCU's dyntick-idle handling.

   - Updates to remove almost all uses of smp_read_barrier_depends() and
     read_barrier_depends().

   - Torture-test updates.

   - Miscellaneous fixes"

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (72 commits)
  torture: Save a line in stutter_wait(): while -> for
  torture: Eliminate torture_runnable and perf_runnable
  torture: Make stutter less vulnerable to compilers and races
  locking/locktorture: Fix num reader/writer corner cases
  locking/locktorture: Fix rwsem reader_delay
  torture: Place all torture-test modules in one MAINTAINERS group
  rcutorture/kvm-build.sh: Skip build directory check
  rcutorture: Simplify functions.sh include path
  rcutorture: Simplify logging
  rcutorture/kvm-recheck-*: Improve result directory readability check
  rcutorture/kvm.sh: Support execution from any directory
  rcutorture/kvm.sh: Use consistent help text for --qemu-args
  rcutorture/kvm.sh: Remove unused variable, `alldone`
  rcutorture: Remove unused script, config2frag.sh
  rcutorture/configinit: Fix build directory error message
  rcutorture: Preempt RCU-preempt readers more vigorously
  torture: Reduce #ifdefs for preempt_schedule()
  rcu: Remove have_rcu_nocb_mask from tree_plugin.h
  rcu: Add comment giving debug strategy for double call_rcu()
  tracing, rcu: Hide trace event rcu_nocb_wake when not used
  ...

2 files changed, 57 insertions, 63 deletions

diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
index f24582d4dad3..6850ffd69125 100644
--- a/kernel/locking/locktorture.c
+++ b/kernel/locking/locktorture.c
@@ -77,10 +77,6 @@ struct lock_stress_stats {
 	long n_lock_acquired;
 };
 
-int torture_runnable = IS_ENABLED(MODULE);
-module_param(torture_runnable, int, 0444);
-MODULE_PARM_DESC(torture_runnable, "Start locktorture at module init");
-
 /* Forward reference. */
 static void lock_torture_cleanup(void);
 
@@ -130,10 +126,8 @@ static void torture_lock_busted_write_delay(struct torture_random_state *trsp)
 	if (!(torture_random(trsp) %
 	      (cxt.nrealwriters_stress * 2000 * longdelay_ms)))
 		mdelay(longdelay_ms);
-#ifdef CONFIG_PREEMPT
 	if (!(torture_random(trsp) % (cxt.nrealwriters_stress * 20000)))
-		preempt_schedule();  /* Allow test to be preempted. */
-#endif
+		torture_preempt_schedule();  /* Allow test to be preempted. */
 }
 
 static void torture_lock_busted_write_unlock(void)
@@ -179,10 +173,8 @@ static void torture_spin_lock_write_delay(struct torture_random_state *trsp)
 	if (!(torture_random(trsp) %
 	      (cxt.nrealwriters_stress * 2 * shortdelay_us)))
 		udelay(shortdelay_us);
-#ifdef CONFIG_PREEMPT
 	if (!(torture_random(trsp) % (cxt.nrealwriters_stress * 20000)))
-		preempt_schedule();  /* Allow test to be preempted. */
-#endif
+		torture_preempt_schedule();  /* Allow test to be preempted. */
 }
 
 static void torture_spin_lock_write_unlock(void) __releases(torture_spinlock)
@@ -352,10 +344,8 @@ static void torture_mutex_delay(struct torture_random_state *trsp)
 		mdelay(longdelay_ms * 5);
 	else
 		mdelay(longdelay_ms / 5);
-#ifdef CONFIG_PREEMPT
 	if (!(torture_random(trsp) % (cxt.nrealwriters_stress * 20000)))
-		preempt_schedule();  /* Allow test to be preempted. */
-#endif
+		torture_preempt_schedule();  /* Allow test to be preempted. */
 }
 
 static void torture_mutex_unlock(void) __releases(torture_mutex)
@@ -507,10 +497,8 @@ static void torture_rtmutex_delay(struct torture_random_state *trsp)
 	if (!(torture_random(trsp) %
 	      (cxt.nrealwriters_stress * 2 * shortdelay_us)))
 		udelay(shortdelay_us);
-#ifdef CONFIG_PREEMPT
 	if (!(torture_random(trsp) % (cxt.nrealwriters_stress * 20000)))
-		preempt_schedule();  /* Allow test to be preempted. */
-#endif
+		torture_preempt_schedule();  /* Allow test to be preempted. */
 }
 
 static void torture_rtmutex_unlock(void) __releases(torture_rtmutex)
@@ -547,10 +535,8 @@ static void torture_rwsem_write_delay(struct torture_random_state *trsp)
 		mdelay(longdelay_ms * 10);
 	else
 		mdelay(longdelay_ms / 10);
-#ifdef CONFIG_PREEMPT
 	if (!(torture_random(trsp) % (cxt.nrealwriters_stress * 20000)))
-		preempt_schedule();  /* Allow test to be preempted. */
-#endif
+		torture_preempt_schedule();  /* Allow test to be preempted. */
 }
 
 static void torture_rwsem_up_write(void) __releases(torture_rwsem)
@@ -570,14 +556,12 @@ static void torture_rwsem_read_delay(struct torture_random_state *trsp)
 
 	/* We want a long delay occasionally to force massive contention.  */
 	if (!(torture_random(trsp) %
-	      (cxt.nrealwriters_stress * 2000 * longdelay_ms)))
+	      (cxt.nrealreaders_stress * 2000 * longdelay_ms)))
 		mdelay(longdelay_ms * 2);
 	else
 		mdelay(longdelay_ms / 2);
-#ifdef CONFIG_PREEMPT
 	if (!(torture_random(trsp) % (cxt.nrealreaders_stress * 20000)))
-		preempt_schedule();  /* Allow test to be preempted. */
-#endif
+		torture_preempt_schedule();  /* Allow test to be preempted. */
 }
 
 static void torture_rwsem_up_read(void) __releases(torture_rwsem)
@@ -715,8 +699,7 @@ static void __torture_print_stats(char *page,
 {
 	bool fail = 0;
 	int i, n_stress;
-	long max = 0;
-	long min = statp[0].n_lock_acquired;
+	long max = 0, min = statp ? statp[0].n_lock_acquired : 0;
 	long long sum = 0;
 
 	n_stress = write ? cxt.nrealwriters_stress : cxt.nrealreaders_stress;
@@ -823,7 +806,7 @@ static void lock_torture_cleanup(void)
 	 * such, only perform the underlying torture-specific cleanups,
 	 * and avoid anything related to locktorture.
 	 */
-	if (!cxt.lwsa)
+	if (!cxt.lwsa && !cxt.lrsa)
 		goto end;
 
 	if (writer_tasks) {
@@ -879,7 +862,7 @@ static int __init lock_torture_init(void)
 		&percpu_rwsem_lock_ops,
 	};
 
-	if (!torture_init_begin(torture_type, verbose, &torture_runnable))
+	if (!torture_init_begin(torture_type, verbose))
 		return -EBUSY;
 
 	/* Process args and tell the world that the torturer is on the job. */
@@ -898,6 +881,13 @@ static int __init lock_torture_init(void)
 		firsterr = -EINVAL;
 		goto unwind;
 	}
+
+	if (nwriters_stress == 0 && nreaders_stress == 0) {
+		pr_alert("lock-torture: must run at least one locking thread\n");
+		firsterr = -EINVAL;
+		goto unwind;
+	}
+
 	if (cxt.cur_ops->init)
 		cxt.cur_ops->init();
 
@@ -921,17 +911,19 @@ static int __init lock_torture_init(void)
 #endif
 
 	/* Initialize the statistics so that each run gets its own numbers. */
+	if (nwriters_stress) {
+		lock_is_write_held = 0;
+		cxt.lwsa = kmalloc(sizeof(*cxt.lwsa) * cxt.nrealwriters_stress, GFP_KERNEL);
+		if (cxt.lwsa == NULL) {
+			VERBOSE_TOROUT_STRING("cxt.lwsa: Out of memory");
+			firsterr = -ENOMEM;
+			goto unwind;
+		}
 
-	lock_is_write_held = 0;
-	cxt.lwsa = kmalloc(sizeof(*cxt.lwsa) * cxt.nrealwriters_stress, GFP_KERNEL);
-	if (cxt.lwsa == NULL) {
-		VERBOSE_TOROUT_STRING("cxt.lwsa: Out of memory");
-		firsterr = -ENOMEM;
-		goto unwind;
-	}
-	for (i = 0; i < cxt.nrealwriters_stress; i++) {
-		cxt.lwsa[i].n_lock_fail = 0;
-		cxt.lwsa[i].n_lock_acquired = 0;
+		for (i = 0; i < cxt.nrealwriters_stress; i++) {
+			cxt.lwsa[i].n_lock_fail = 0;
+			cxt.lwsa[i].n_lock_acquired = 0;
+		}
 	}
 
 	if (cxt.cur_ops->readlock) {
@@ -948,19 +940,21 @@ static int __init lock_torture_init(void)
 			cxt.nrealreaders_stress = cxt.nrealwriters_stress;
 		}
 
-		lock_is_read_held = 0;
-		cxt.lrsa = kmalloc(sizeof(*cxt.lrsa) * cxt.nrealreaders_stress, GFP_KERNEL);
-		if (cxt.lrsa == NULL) {
-			VERBOSE_TOROUT_STRING("cxt.lrsa: Out of memory");
-			firsterr = -ENOMEM;
-			kfree(cxt.lwsa);
-			cxt.lwsa = NULL;
-			goto unwind;
-		}
-
-		for (i = 0; i < cxt.nrealreaders_stress; i++) {
-			cxt.lrsa[i].n_lock_fail = 0;
-			cxt.lrsa[i].n_lock_acquired = 0;
+		if (nreaders_stress) {
+			lock_is_read_held = 0;
+			cxt.lrsa = kmalloc(sizeof(*cxt.lrsa) * cxt.nrealreaders_stress, GFP_KERNEL);
+			if (cxt.lrsa == NULL) {
+				VERBOSE_TOROUT_STRING("cxt.lrsa: Out of memory");
+				firsterr = -ENOMEM;
+				kfree(cxt.lwsa);
+				cxt.lwsa = NULL;
+				goto unwind;
+			}
+
+			for (i = 0; i < cxt.nrealreaders_stress; i++) {
+				cxt.lrsa[i].n_lock_fail = 0;
+				cxt.lrsa[i].n_lock_acquired = 0;
+			}
 		}
 	}
 
@@ -990,12 +984,14 @@ static int __init lock_torture_init(void)
 			goto unwind;
 	}
 
-	writer_tasks = kzalloc(cxt.nrealwriters_stress * sizeof(writer_tasks[0]),
-			       GFP_KERNEL);
-	if (writer_tasks == NULL) {
-		VERBOSE_TOROUT_ERRSTRING("writer_tasks: Out of memory");
-		firsterr = -ENOMEM;
-		goto unwind;
+	if (nwriters_stress) {
+		writer_tasks = kzalloc(cxt.nrealwriters_stress * sizeof(writer_tasks[0]),
+				       GFP_KERNEL);
+		if (writer_tasks == NULL) {
+			VERBOSE_TOROUT_ERRSTRING("writer_tasks: Out of memory");
+			firsterr = -ENOMEM;
+			goto unwind;
+		}
 	}
 
 	if (cxt.cur_ops->readlock) {
diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index 294294c71ba4..38ece035039e 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -170,7 +170,7 @@ static __always_inline void clear_pending_set_locked(struct qspinlock *lock)
  * @tail : The new queue tail code word
  * Return: The previous queue tail code word
  *
- * xchg(lock, tail)
+ * xchg(lock, tail), which heads an address dependency
  *
  * p,*,* -> n,*,* ; prev = xchg(lock, node)
  */
@@ -409,13 +409,11 @@ queue:
 	if (old & _Q_TAIL_MASK) {
 		prev = decode_tail(old);
 		/*
-		 * The above xchg_tail() is also a load of @lock which generates,
-		 * through decode_tail(), a pointer.
-		 *
-		 * The address dependency matches the RELEASE of xchg_tail()
-		 * such that the access to @prev must happen after.
+		 * The above xchg_tail() is also a load of @lock which
+		 * generates, through decode_tail(), a pointer.  The address
+		 * dependency matches the RELEASE of xchg_tail() such that
+		 * the subsequent access to @prev happens after.
 		 */
-		smp_read_barrier_depends();
 
 		WRITE_ONCE(prev->next, node);