Merge branch 'rcu-tasks.2014.09.10a' into HEAD

rcu-tasks.2014.09.10a: Add RCU-tasks flavor of RCU.

Documentation/RCU/stallwarn.txt

@@ -56,8 +56,20 @@ RCU_STALL_RAT_DELAY
 	two jiffies.  (This is a cpp macro, not a kernel configuration
 	parameter.)
 
-When a CPU detects that it is stalling, it will print a message similar
-to the following:
+rcupdate.rcu_task_stall_timeout
+
+	This boot/sysfs parameter controls the RCU-tasks stall warning
+	interval.  A value of zero or less suppresses RCU-tasks stall
+	warnings.  A positive value sets the stall-warning interval
+	in jiffies.  An RCU-tasks stall warning starts wtih the line:
+
+		INFO: rcu_tasks detected stalls on tasks:
+
+	And continues with the output of sched_show_task() for each
+	task stalling the current RCU-tasks grace period.
+
+For non-RCU-tasks flavors of RCU, when a CPU detects that it is stalling,
+it will print a message similar to the following:
 
 INFO: rcu_sched_state detected stall on CPU 5 (t=2500 jiffies)
 
@@ -174,8 +186,12 @@ o	A CPU looping with preemption disabled.  This condition can
 o	A CPU looping with bottom halves disabled.  This condition can
 	result in RCU-sched and RCU-bh stalls.
 
-o	For !CONFIG_PREEMPT kernels, a CPU looping anywhere in the kernel
-	without invoking schedule().
+o	For !CONFIG_PREEMPT kernels, a CPU looping anywhere in the
+	kernel without invoking schedule().  Note that cond_resched()
+	does not necessarily prevent RCU CPU stall warnings.  Therefore,
+	if the looping in the kernel is really expected and desirable
+	behavior, you might need to replace some of the cond_resched()
+	calls with calls to cond_resched_rcu_qs().
 
 o	A CPU-bound real-time task in a CONFIG_PREEMPT kernel, which might
 	happen to preempt a low-priority task in the middle of an RCU
@@ -208,11 +224,10 @@ o	A hardware failure.  This is quite unlikely, but has occurred
 	This resulted in a series of RCU CPU stall warnings, eventually
 	leading the realization that the CPU had failed.
 
-The RCU, RCU-sched, and RCU-bh implementations have CPU stall warning.
-SRCU does not have its own CPU stall warnings, but its calls to
-synchronize_sched() will result in RCU-sched detecting RCU-sched-related
-CPU stalls.  Please note that RCU only detects CPU stalls when there is
-a grace period in progress.  No grace period, no CPU stall warnings.
+The RCU, RCU-sched, RCU-bh, and RCU-tasks implementations have CPU stall
+warning.  Note that SRCU does -not- have CPU stall warnings.  Please note
+that RCU only detects CPU stalls when there is a grace period in progress.
+No grace period, no CPU stall warnings.
 
 To diagnose the cause of the stall, inspect the stack traces.
 The offending function will usually be near the top of the stack.

Documentation/kernel-parameters.txt

@@ -3000,6 +3000,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 	rcupdate.rcu_cpu_stall_timeout= [KNL]
 			Set timeout for RCU CPU stall warning messages.
 
+	rcupdate.rcu_task_stall_timeout= [KNL]
+			Set timeout in jiffies for RCU task stall warning
+			messages.  Disable with a value less than or equal
+			to zero.
+
 	rdinit=		[KNL]
 			Format: <full_path>
 			Run specified binary instead of /init from the ramdisk,

fs/file.c

@@ -367,7 +367,7 @@ static struct fdtable *close_files(struct files_struct * files)
 				struct file * file = xchg(&fdt->fd[i], NULL);
 				if (file) {
 					filp_close(file, files);
-					cond_resched();
+					cond_resched_rcu_qs();
 				}
 			}
 			i++;

include/linux/init_task.h

@@ -111,12 +111,21 @@ extern struct group_info init_groups;
 #ifdef CONFIG_PREEMPT_RCU
 #define INIT_TASK_RCU_PREEMPT(tsk)					\
 	.rcu_read_lock_nesting = 0,					\
-	.rcu_read_unlock_special = 0,					\
+	.rcu_read_unlock_special.s = 0,					\
 	.rcu_node_entry = LIST_HEAD_INIT(tsk.rcu_node_entry),		\
 	INIT_TASK_RCU_TREE_PREEMPT()
 #else
 #define INIT_TASK_RCU_PREEMPT(tsk)
 #endif
+#ifdef CONFIG_TASKS_RCU
+#define INIT_TASK_RCU_TASKS(tsk)					\
+	.rcu_tasks_holdout = false,					\
+	.rcu_tasks_holdout_list =					\
+		LIST_HEAD_INIT(tsk.rcu_tasks_holdout_list),		\
+	.rcu_tasks_idle_cpu = -1,
+#else
+#define INIT_TASK_RCU_TASKS(tsk)
+#endif
 
 extern struct cred init_cred;
 
@@ -224,6 +233,7 @@ extern struct task_group root_task_group;
 	INIT_FTRACE_GRAPH						\
 	INIT_TRACE_RECURSION						\
 	INIT_TASK_RCU_PREEMPT(tsk)					\
+	INIT_TASK_RCU_TASKS(tsk)					\
 	INIT_CPUSET_SEQ(tsk)						\
 	INIT_RT_MUTEXES(tsk)						\
 	INIT_VTIME(tsk)							\

include/linux/rcupdate.h

@@ -55,6 +55,7 @@ enum rcutorture_type {
 	RCU_FLAVOR,
 	RCU_BH_FLAVOR,
 	RCU_SCHED_FLAVOR,
+	RCU_TASKS_FLAVOR,
 	SRCU_FLAVOR,
 	INVALID_RCU_FLAVOR
 };
@@ -197,6 +198,28 @@ void call_rcu_sched(struct rcu_head *head,
 
 void synchronize_sched(void);
 
+/**
+ * call_rcu_tasks() - Queue an RCU for invocation task-based grace period
+ * @head: structure to be used for queueing the RCU updates.
+ * @func: actual callback function to be invoked after the grace period
+ *
+ * The callback function will be invoked some time after a full grace
+ * period elapses, in other words after all currently executing RCU
+ * read-side critical sections have completed. call_rcu_tasks() assumes
+ * that the read-side critical sections end at a voluntary context
+ * switch (not a preemption!), entry into idle, or transition to usermode
+ * execution.  As such, there are no read-side primitives analogous to
+ * rcu_read_lock() and rcu_read_unlock() because this primitive is intended
+ * to determine that all tasks have passed through a safe state, not so
+ * much for data-strcuture synchronization.
+ *
+ * See the description of call_rcu() for more detailed information on
+ * memory ordering guarantees.
+ */
+void call_rcu_tasks(struct rcu_head *head, void (*func)(struct rcu_head *head));
+void synchronize_rcu_tasks(void);
+void rcu_barrier_tasks(void);
+
 #ifdef CONFIG_PREEMPT_RCU
 
 void __rcu_read_lock(void);
@@ -238,8 +261,8 @@ static inline int rcu_preempt_depth(void)
 
 /* Internal to kernel */
 void rcu_init(void);
-void rcu_sched_qs(int cpu);
-void rcu_bh_qs(int cpu);
+void rcu_sched_qs(void);
+void rcu_bh_qs(void);
 void rcu_check_callbacks(int cpu, int user);
 struct notifier_block;
 void rcu_idle_enter(void);
@@ -302,6 +325,36 @@ static inline void rcu_init_nohz(void)
 		rcu_irq_exit(); \
 	} while (0)
 
+/*
+ * Note a voluntary context switch for RCU-tasks benefit.  This is a
+ * macro rather than an inline function to avoid #include hell.
+ */
+#ifdef CONFIG_TASKS_RCU
+#define TASKS_RCU(x) x
+extern struct srcu_struct tasks_rcu_exit_srcu;
+#define rcu_note_voluntary_context_switch(t) \
+	do { \
+		if (ACCESS_ONCE((t)->rcu_tasks_holdout)) \
+			ACCESS_ONCE((t)->rcu_tasks_holdout) = false; \
+	} while (0)
+#else /* #ifdef CONFIG_TASKS_RCU */
+#define TASKS_RCU(x) do { } while (0)
+#define rcu_note_voluntary_context_switch(t)	do { } while (0)
+#endif /* #else #ifdef CONFIG_TASKS_RCU */
+
+/**
+ * cond_resched_rcu_qs - Report potential quiescent states to RCU
+ *
+ * This macro resembles cond_resched(), except that it is defined to
+ * report potential quiescent states to RCU-tasks even if the cond_resched()
+ * machinery were to be shut off, as some advocate for PREEMPT kernels.
+ */
+#define cond_resched_rcu_qs() \
+do { \
+	rcu_note_voluntary_context_switch(current); \
+	cond_resched(); \
+} while (0)
+
 #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP)
 bool __rcu_is_watching(void);
 #endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP) */

include/linux/rcutiny.h

@@ -80,7 +80,7 @@ static inline void kfree_call_rcu(struct rcu_head *head,
 
 static inline void rcu_note_context_switch(int cpu)
 {
-	rcu_sched_qs(cpu);
+	rcu_sched_qs();
 }
 
 /*

include/linux/sched.h

@@ -1212,6 +1212,13 @@ struct sched_dl_entity {
 	struct hrtimer dl_timer;
 };
 
+union rcu_special {
+	struct {
+		bool blocked;
+		bool need_qs;
+	} b;
+	short s;
+};
 struct rcu_node;
 
 enum perf_event_task_context {
@@ -1264,12 +1271,18 @@ struct task_struct {
 
 #ifdef CONFIG_PREEMPT_RCU
 	int rcu_read_lock_nesting;
-	char rcu_read_unlock_special;
+	union rcu_special rcu_read_unlock_special;
 	struct list_head rcu_node_entry;
 #endif /* #ifdef CONFIG_PREEMPT_RCU */
 #ifdef CONFIG_TREE_PREEMPT_RCU
 	struct rcu_node *rcu_blocked_node;
 #endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
+#ifdef CONFIG_TASKS_RCU
+	unsigned long rcu_tasks_nvcsw;
+	bool rcu_tasks_holdout;
+	struct list_head rcu_tasks_holdout_list;
+	int rcu_tasks_idle_cpu;
+#endif /* #ifdef CONFIG_TASKS_RCU */
 
 #if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
 	struct sched_info sched_info;
@@ -1999,29 +2012,21 @@ extern void task_clear_jobctl_trapping(struct task_struct *task);
 extern void task_clear_jobctl_pending(struct task_struct *task,
 				      unsigned int mask);
 
-#ifdef CONFIG_PREEMPT_RCU
-
-#define RCU_READ_UNLOCK_BLOCKED (1 << 0) /* blocked while in RCU read-side. */
-#define RCU_READ_UNLOCK_NEED_QS (1 << 1) /* RCU core needs CPU response. */
-
 static inline void rcu_copy_process(struct task_struct *p)
 {
+#ifdef CONFIG_PREEMPT_RCU
 	p->rcu_read_lock_nesting = 0;
-	p->rcu_read_unlock_special = 0;
-#ifdef CONFIG_TREE_PREEMPT_RCU
+	p->rcu_read_unlock_special.s = 0;
 	p->rcu_blocked_node = NULL;
-#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
 	INIT_LIST_HEAD(&p->rcu_node_entry);
+#endif /* #ifdef CONFIG_PREEMPT_RCU */
+#ifdef CONFIG_TASKS_RCU
+	p->rcu_tasks_holdout = false;
+	INIT_LIST_HEAD(&p->rcu_tasks_holdout_list);
+	p->rcu_tasks_idle_cpu = -1;
+#endif /* #ifdef CONFIG_TASKS_RCU */
 }
 
-#else
-
-static inline void rcu_copy_process(struct task_struct *p)
-{
-}
-
-#endif
-
 static inline void tsk_restore_flags(struct task_struct *task,
 				unsigned long orig_flags, unsigned long flags)
 {

init/Kconfig

@@ -507,6 +507,16 @@ config PREEMPT_RCU
 	  This option enables preemptible-RCU code that is common between
 	  TREE_PREEMPT_RCU and, in the old days, TINY_PREEMPT_RCU.
 
+config TASKS_RCU
+	bool "Task_based RCU implementation using voluntary context switch"
+	default n
+	help
+	  This option enables a task-based RCU implementation that uses
+	  only voluntary context switch (not preemption!), idle, and
+	  user-mode execution as quiescent states.
+
+	  If unsure, say N.
+
 config RCU_STALL_COMMON
 	def_bool ( TREE_RCU || TREE_PREEMPT_RCU || RCU_TRACE )
 	help

kernel/exit.c

@@ -667,6 +667,7 @@ void do_exit(long code)
 {
 	struct task_struct *tsk = current;
 	int group_dead;
+	TASKS_RCU(int tasks_rcu_i);
 
 	profile_task_exit(tsk);
 
@@ -775,6 +776,7 @@ void do_exit(long code)
 	 */
 	flush_ptrace_hw_breakpoint(tsk);
 
+	TASKS_RCU(tasks_rcu_i = __srcu_read_lock(&tasks_rcu_exit_srcu));
 	exit_notify(tsk, group_dead);
 	proc_exit_connector(tsk);
 #ifdef CONFIG_NUMA
@@ -814,6 +816,7 @@ void do_exit(long code)
 	if (tsk->nr_dirtied)
 		__this_cpu_add(dirty_throttle_leaks, tsk->nr_dirtied);
 	exit_rcu();
+	TASKS_RCU(__srcu_read_unlock(&tasks_rcu_exit_srcu, tasks_rcu_i));
 
 	/*
 	 * The setting of TASK_RUNNING by try_to_wake_up() may be delayed

kernel/rcu/rcutorture.c

@@ -612,6 +612,52 @@ static struct rcu_torture_ops sched_ops = {
 	.name		= "sched"
 };
 
+#ifdef CONFIG_TASKS_RCU
+
+/*
+ * Definitions for RCU-tasks torture testing.
+ */
+
+static int tasks_torture_read_lock(void)
+{
+	return 0;
+}
+
+static void tasks_torture_read_unlock(int idx)
+{
+}
+
+static void rcu_tasks_torture_deferred_free(struct rcu_torture *p)
+{
+	call_rcu_tasks(&p->rtort_rcu, rcu_torture_cb);
+}
+
+static struct rcu_torture_ops tasks_ops = {
+	.ttype		= RCU_TASKS_FLAVOR,
+	.init		= rcu_sync_torture_init,
+	.readlock	= tasks_torture_read_lock,
+	.read_delay	= rcu_read_delay,  /* just reuse rcu's version. */
+	.readunlock	= tasks_torture_read_unlock,
+	.completed	= rcu_no_completed,
+	.deferred_free	= rcu_tasks_torture_deferred_free,
+	.sync		= synchronize_rcu_tasks,
+	.exp_sync	= synchronize_rcu_tasks,
+	.call		= call_rcu_tasks,
+	.cb_barrier	= rcu_barrier_tasks,
+	.fqs		= NULL,
+	.stats		= NULL,
+	.irq_capable	= 1,
+	.name		= "tasks"
+};
+
+#define RCUTORTURE_TASKS_OPS &tasks_ops,
+
+#else /* #ifdef CONFIG_TASKS_RCU */
+
+#define RCUTORTURE_TASKS_OPS
+
+#endif /* #else #ifdef CONFIG_TASKS_RCU */
+
 /*
  * RCU torture priority-boost testing.  Runs one real-time thread per
  * CPU for moderate bursts, repeatedly registering RCU callbacks and
@@ -678,7 +724,7 @@ static int rcu_torture_boost(void *arg)
 				}
 				call_rcu_time = jiffies;
 			}
-			cond_resched();
+			cond_resched_rcu_qs();
 			stutter_wait("rcu_torture_boost");
 			if (torture_must_stop())
 				goto checkwait;
@@ -1082,7 +1128,7 @@ rcu_torture_reader(void *arg)
 		__this_cpu_inc(rcu_torture_batch[completed]);
 		preempt_enable();
 		cur_ops->readunlock(idx);
-		cond_resched();
+		cond_resched_rcu_qs();
 		stutter_wait("rcu_torture_reader");
 	} while (!torture_must_stop());
 	if (irqreader && cur_ops->irq_capable) {
@@ -1344,7 +1390,8 @@ static int rcu_torture_barrier_cbs(void *arg)
 		if (atomic_dec_and_test(&barrier_cbs_count))
 			wake_up(&barrier_wq);
 	} while (!torture_must_stop());
-	cur_ops->cb_barrier();
+	if (cur_ops->cb_barrier != NULL)
+		cur_ops->cb_barrier();
 	destroy_rcu_head_on_stack(&rcu);
 	torture_kthread_stopping("rcu_torture_barrier_cbs");
 	return 0;
@@ -1585,6 +1632,7 @@ rcu_torture_init(void)
 	int firsterr = 0;
 	static struct rcu_torture_ops *torture_ops[] = {
 		&rcu_ops, &rcu_bh_ops, &rcu_busted_ops, &srcu_ops, &sched_ops,
+		RCUTORTURE_TASKS_OPS
 	};
 
 	if (!torture_init_begin(torture_type, verbose, &rcutorture_runnable))

kernel/rcu/tiny.c

@@ -72,7 +72,7 @@ static void rcu_idle_enter_common(long long newval)
 			  current->pid, current->comm,
 			  idle->pid, idle->comm); /* must be idle task! */
 	}
-	rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
+	rcu_sched_qs(); /* implies rcu_bh_inc() */
 	barrier();
 	rcu_dynticks_nesting = newval;
 }
@@ -217,7 +217,7 @@ static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
  * are at it, given that any rcu quiescent state is also an rcu_bh
  * quiescent state.  Use "+" instead of "||" to defeat short circuiting.
  */
-void rcu_sched_qs(int cpu)
+void rcu_sched_qs(void)
 {
 	unsigned long flags;
 
@@ -231,7 +231,7 @@ void rcu_sched_qs(int cpu)
 /*
  * Record an rcu_bh quiescent state.
  */
-void rcu_bh_qs(int cpu)
+void rcu_bh_qs(void)
 {
 	unsigned long flags;
 
@@ -251,9 +251,11 @@ void rcu_check_callbacks(int cpu, int user)
 {
 	RCU_TRACE(check_cpu_stalls());
 	if (user || rcu_is_cpu_rrupt_from_idle())
-		rcu_sched_qs(cpu);
+		rcu_sched_qs();
 	else if (!in_softirq())
-		rcu_bh_qs(cpu);
+		rcu_bh_qs();
+	if (user)
+		rcu_note_voluntary_context_switch(current);
 }
 
 /*

kernel/rcu/tree.c

@@ -197,22 +197,24 @@ static int rcu_gp_in_progress(struct rcu_state *rsp)
  * one since the start of the grace period, this just sets a flag.
  * The caller must have disabled preemption.
  */
-void rcu_sched_qs(int cpu)
+void rcu_sched_qs(void)
 {
-	struct rcu_data *rdp = &per_cpu(rcu_sched_data, cpu);
-
-	if (rdp->passed_quiesce == 0)
-		trace_rcu_grace_period(TPS("rcu_sched"), rdp->gpnum, TPS("cpuqs"));
-	rdp->passed_quiesce = 1;
+	if (!__this_cpu_read(rcu_sched_data.passed_quiesce)) {
+		trace_rcu_grace_period(TPS("rcu_sched"),
+				       __this_cpu_read(rcu_sched_data.gpnum),
+				       TPS("cpuqs"));
+		__this_cpu_write(rcu_sched_data.passed_quiesce, 1);
+	}
 }
 
-void rcu_bh_qs(int cpu)
+void rcu_bh_qs(void)
 {
-	struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);
-
-	if (rdp->passed_quiesce == 0)
-		trace_rcu_grace_period(TPS("rcu_bh"), rdp->gpnum, TPS("cpuqs"));
-	rdp->passed_quiesce = 1;
+	if (!__this_cpu_read(rcu_bh_data.passed_quiesce)) {
+		trace_rcu_grace_period(TPS("rcu_bh"),
+				       __this_cpu_read(rcu_bh_data.gpnum),
+				       TPS("cpuqs"));
+		__this_cpu_write(rcu_bh_data.passed_quiesce, 1);
+	}
 }
 
 static DEFINE_PER_CPU(int, rcu_sched_qs_mask);
@@ -287,7 +289,7 @@ static void rcu_momentary_dyntick_idle(void)
 void rcu_note_context_switch(int cpu)
 {
 	trace_rcu_utilization(TPS("Start context switch"));
-	rcu_sched_qs(cpu);
+	rcu_sched_qs();
 	rcu_preempt_note_context_switch(cpu);
 	if (unlikely(raw_cpu_read(rcu_sched_qs_mask)))
 		rcu_momentary_dyntick_idle();
@@ -535,6 +537,7 @@ static void rcu_eqs_enter_common(struct rcu_dynticks *rdtp, long long oldval,
 	atomic_inc(&rdtp->dynticks);
 	smp_mb__after_atomic();  /* Force ordering with next sojourn. */
 	WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
+	rcu_dynticks_task_enter();
 
 	/*
 	 * It is illegal to enter an extended quiescent state while
@@ -651,6 +654,7 @@ void rcu_irq_exit(void)
 static void rcu_eqs_exit_common(struct rcu_dynticks *rdtp, long long oldval,
 			       int user)
 {
+	rcu_dynticks_task_exit();
 	smp_mb__before_atomic();  /* Force ordering w/previous sojourn. */
 	atomic_inc(&rdtp->dynticks);
 	/* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
@@ -1656,7 +1660,7 @@ static int rcu_gp_init(struct rcu_state *rsp)
 					    rnp->level, rnp->grplo,
 					    rnp->grphi, rnp->qsmask);
 		raw_spin_unlock_irq(&rnp->lock);
-		cond_resched();
+		cond_resched_rcu_qs();
 	}
 
 	mutex_unlock(&rsp->onoff_mutex);
@@ -1746,7 +1750,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
 		/* smp_mb() provided by prior unlock-lock pair. */
 		nocb += rcu_future_gp_cleanup(rsp, rnp);
 		raw_spin_unlock_irq(&rnp->lock);
-		cond_resched();
+		cond_resched_rcu_qs();
 	}
 	rnp = rcu_get_root(rsp);
 	raw_spin_lock_irq(&rnp->lock);
@@ -1795,7 +1799,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
 			/* Locking provides needed memory barrier. */
 			if (rcu_gp_init(rsp))
 				break;
-			cond_resched();
+			cond_resched_rcu_qs();
 			WARN_ON(signal_pending(current));
 			trace_rcu_grace_period(rsp->name,
 					       ACCESS_ONCE(rsp->gpnum),
@@ -1838,10 +1842,10 @@ static int __noreturn rcu_gp_kthread(void *arg)
 				trace_rcu_grace_period(rsp->name,
 						       ACCESS_ONCE(rsp->gpnum),
 						       TPS("fqsend"));
-				cond_resched();
+				cond_resched_rcu_qs();
 			} else {
 				/* Deal with stray signal. */
-				cond_resched();
+				cond_resched_rcu_qs();
 				WARN_ON(signal_pending(current));
 				trace_rcu_grace_period(rsp->name,
 						       ACCESS_ONCE(rsp->gpnum),
@@ -2401,8 +2405,8 @@ void rcu_check_callbacks(int cpu, int user)
 		 * at least not while the corresponding CPU is online.
 		 */
 
-		rcu_sched_qs(cpu);
-		rcu_bh_qs(cpu);
+		rcu_sched_qs();
+		rcu_bh_qs();
 
 	} else if (!in_softirq()) {
 
@@ -2413,11 +2417,13 @@ void rcu_check_callbacks(int cpu, int user)
 		 * critical section, so note it.
 		 */
 
-		rcu_bh_qs(cpu);
+		rcu_bh_qs();
 	}
 	rcu_preempt_check_callbacks(cpu);
 	if (rcu_pending(cpu))
 		invoke_rcu_core();
+	if (user)
+		rcu_note_voluntary_context_switch(current);
 	trace_rcu_utilization(TPS("End scheduler-tick"));
 }
 
@@ -2440,7 +2446,7 @@ static void force_qs_rnp(struct rcu_state *rsp,
 	struct rcu_node *rnp;
 
 	rcu_for_each_leaf_node(rsp, rnp) {
-		cond_resched();
+		cond_resched_rcu_qs();
 		mask = 0;
 		raw_spin_lock_irqsave(&rnp->lock, flags);
 		smp_mb__after_unlock_lock();

kernel/rcu/tree.h

@@ -615,6 +615,8 @@ static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
 static void rcu_bind_gp_kthread(void);
 static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp);
 static bool rcu_nohz_full_cpu(struct rcu_state *rsp);
+static void rcu_dynticks_task_enter(void);
+static void rcu_dynticks_task_exit(void);
 
 #endif /* #ifndef RCU_TREE_NONCORE */
 

kernel/rcu/tree_plugin.h

@@ -128,18 +128,19 @@ EXPORT_SYMBOL_GPL(rcu_batches_completed);
  * not in a quiescent state.  There might be any number of tasks blocked
  * while in an RCU read-side critical section.
  *
- * Unlike the other rcu_*_qs() functions, callers to this function
- * must disable irqs in order to protect the assignment to
- * ->rcu_read_unlock_special.
- */
-static void rcu_preempt_qs(int cpu)
-{
-	struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
-
-	if (rdp->passed_quiesce == 0)
-		trace_rcu_grace_period(TPS("rcu_preempt"), rdp->gpnum, TPS("cpuqs"));
-	rdp->passed_quiesce = 1;
-	current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
+ * As with the other rcu_*_qs() functions, callers to this function
+ * must disable preemption.
+ */
+static void rcu_preempt_qs(void)
+{
+	if (!__this_cpu_read(rcu_preempt_data.passed_quiesce)) {
+		trace_rcu_grace_period(TPS("rcu_preempt"),
+				       __this_cpu_read(rcu_preempt_data.gpnum),
+				       TPS("cpuqs"));
+		__this_cpu_write(rcu_preempt_data.passed_quiesce, 1);
+		barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */
+		current->rcu_read_unlock_special.b.need_qs = false;
+	}
 }
 
 /*
@@ -163,14 +164,14 @@ static void rcu_preempt_note_context_switch(int cpu)
 	struct rcu_node *rnp;
 
 	if (t->rcu_read_lock_nesting > 0 &&
-	    (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
+	    !t->rcu_read_unlock_special.b.blocked) {
 
 		/* Possibly blocking in an RCU read-side critical section. */
 		rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
 		rnp = rdp->mynode;
 		raw_spin_lock_irqsave(&rnp->lock, flags);
 		smp_mb__after_unlock_lock();
-		t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
+		t->rcu_read_unlock_special.b.blocked = true;
 		t->rcu_blocked_node = rnp;
 
 		/*
@@ -212,7 +213,7 @@ static void rcu_preempt_note_context_switch(int cpu)
 				       : rnp->gpnum + 1);
 		raw_spin_unlock_irqrestore(&rnp->lock, flags);
 	} else if (t->rcu_read_lock_nesting < 0 &&
-		   t->rcu_read_unlock_special) {
+		   t->rcu_read_unlock_special.s) {
 
 		/*
 		 * Complete exit from RCU read-side critical section on
@@ -230,9 +231,7 @@ static void rcu_preempt_note_context_switch(int cpu)
 	 * grace period, then the fact that the task has been enqueued
 	 * means that we continue to block the current grace period.
 	 */
-	local_irq_save(flags);
-	rcu_preempt_qs(cpu);
-	local_irq_restore(flags);
+	rcu_preempt_qs();
 }
 
 /*
@@ -313,7 +312,7 @@ void rcu_read_unlock_special(struct task_struct *t)
 	bool drop_boost_mutex = false;
 #endif /* #ifdef CONFIG_RCU_BOOST */
 	struct rcu_node *rnp;
-	int special;
+	union rcu_special special;
 
 	/* NMI handlers cannot block and cannot safely manipulate state. */
 	if (in_nmi())
@@ -323,12 +322,13 @@ void rcu_read_unlock_special(struct task_struct *t)
 
 	/*
 	 * If RCU core is waiting for this CPU to exit critical section,
-	 * let it know that we have done so.
+	 * let it know that we have done so.  Because irqs are disabled,
+	 * t->rcu_read_unlock_special cannot change.
 	 */
 	special = t->rcu_read_unlock_special;
-	if (special & RCU_READ_UNLOCK_NEED_QS) {
-		rcu_preempt_qs(smp_processor_id());
-		if (!t->rcu_read_unlock_special) {
+	if (special.b.need_qs) {
+		rcu_preempt_qs();
+		if (!t->rcu_read_unlock_special.s) {
 			local_irq_restore(flags);
 			return;
 		}
@@ -341,8 +341,8 @@ void rcu_read_unlock_special(struct task_struct *t)
 	}
 
 	/* Clean up if blocked during RCU read-side critical section. */
-	if (special & RCU_READ_UNLOCK_BLOCKED) {
-		t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
+	if (special.b.blocked) {
+		t->rcu_read_unlock_special.b.blocked = false;
 
 		/*
 		 * Remove this task from the list it blocked on.  The
@@ -626,12 +626,13 @@ static void rcu_preempt_check_callbacks(int cpu)
 	struct task_struct *t = current;
 
 	if (t->rcu_read_lock_nesting == 0) {
-		rcu_preempt_qs(cpu);
+		rcu_preempt_qs();
 		return;
 	}
 	if (t->rcu_read_lock_nesting > 0 &&
-	    per_cpu(rcu_preempt_data, cpu).qs_pending)
-		t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
+	    per_cpu(rcu_preempt_data, cpu).qs_pending &&
+	    !per_cpu(rcu_preempt_data, cpu).passed_quiesce)
+		t->rcu_read_unlock_special.b.need_qs = true;
 }
 
 #ifdef CONFIG_RCU_BOOST
@@ -915,7 +916,7 @@ void exit_rcu(void)
 		return;
 	t->rcu_read_lock_nesting = 1;
 	barrier();
-	t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
+	t->rcu_read_unlock_special.b.blocked = true;
 	__rcu_read_unlock();
 }
 
@@ -1816,7 +1817,7 @@ static int rcu_oom_notify(struct notifier_block *self,
 	get_online_cpus();
 	for_each_online_cpu(cpu) {
 		smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
-		cond_resched();
+		cond_resched_rcu_qs();
 	}
 	put_online_cpus();
 
@@ -3162,3 +3163,19 @@ static void rcu_bind_gp_kthread(void)
 		housekeeping_affine(current);
 #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
 }
+
+/* Record the current task on dyntick-idle entry. */
+static void rcu_dynticks_task_enter(void)
+{
+#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
+	ACCESS_ONCE(current->rcu_tasks_idle_cpu) = smp_processor_id();
+#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
+}
+
+/* Record no current task on dyntick-idle exit. */
+static void rcu_dynticks_task_exit(void)
+{
+#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
+	ACCESS_ONCE(current->rcu_tasks_idle_cpu) = -1;
+#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
+}

kernel/rcu/update.c

@@ -47,6 +47,8 @@
 #include <linux/hardirq.h>
 #include <linux/delay.h>
 #include <linux/module.h>
+#include <linux/kthread.h>
+#include <linux/tick.h>
 
 #define CREATE_TRACE_POINTS
 
@@ -91,7 +93,7 @@ void __rcu_read_unlock(void)
 		barrier();  /* critical section before exit code. */
 		t->rcu_read_lock_nesting = INT_MIN;
 		barrier();  /* assign before ->rcu_read_unlock_special load */
-		if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
+		if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special.s)))
 			rcu_read_unlock_special(t);
 		barrier();  /* ->rcu_read_unlock_special load before assign */
 		t->rcu_read_lock_nesting = 0;
@@ -379,3 +381,312 @@ static int __init check_cpu_stall_init(void)
 early_initcall(check_cpu_stall_init);
 
 #endif /* #ifdef CONFIG_RCU_STALL_COMMON */
+
+#ifdef CONFIG_TASKS_RCU
+
+/*
+ * Simple variant of RCU whose quiescent states are voluntary context switch,
+ * user-space execution, and idle.  As such, grace periods can take one good
+ * long time.  There are no read-side primitives similar to rcu_read_lock()
+ * and rcu_read_unlock() because this implementation is intended to get
+ * the system into a safe state for some of the manipulations involved in
+ * tracing and the like.  Finally, this implementation does not support
+ * high call_rcu_tasks() rates from multiple CPUs.  If this is required,
+ * per-CPU callback lists will be needed.
+ */
+
+/* Global list of callbacks and associated lock. */
+static struct rcu_head *rcu_tasks_cbs_head;
+static struct rcu_head **rcu_tasks_cbs_tail = &rcu_tasks_cbs_head;
+static DECLARE_WAIT_QUEUE_HEAD(rcu_tasks_cbs_wq);
+static DEFINE_RAW_SPINLOCK(rcu_tasks_cbs_lock);
+
+/* Track exiting tasks in order to allow them to be waited for. */
+DEFINE_SRCU(tasks_rcu_exit_srcu);
+
+/* Control stall timeouts.  Disable with <= 0, otherwise jiffies till stall. */
+static int rcu_task_stall_timeout __read_mostly = HZ * 60 * 10;
+module_param(rcu_task_stall_timeout, int, 0644);
+
+static void rcu_spawn_tasks_kthread(void);
+
+/*
+ * Post an RCU-tasks callback.  First call must be from process context
+ * after the scheduler if fully operational.
+ */
+void call_rcu_tasks(struct rcu_head *rhp, void (*func)(struct rcu_head *rhp))
+{
+	unsigned long flags;
+	bool needwake;
+
+	rhp->next = NULL;
+	rhp->func = func;
+	raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags);
+	needwake = !rcu_tasks_cbs_head;
+	*rcu_tasks_cbs_tail = rhp;
+	rcu_tasks_cbs_tail = &rhp->next;
+	raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags);
+	if (needwake) {
+		rcu_spawn_tasks_kthread();
+		wake_up(&rcu_tasks_cbs_wq);
+	}
+}
+EXPORT_SYMBOL_GPL(call_rcu_tasks);
+
+/**
+ * synchronize_rcu_tasks - wait until an rcu-tasks grace period has elapsed.
+ *
+ * Control will return to the caller some time after a full rcu-tasks
+ * grace period has elapsed, in other words after all currently
+ * executing rcu-tasks read-side critical sections have elapsed.  These
+ * read-side critical sections are delimited by calls to schedule(),
+ * cond_resched_rcu_qs(), idle execution, userspace execution, calls
+ * to synchronize_rcu_tasks(), and (in theory, anyway) cond_resched().
+ *
+ * This is a very specialized primitive, intended only for a few uses in
+ * tracing and other situations requiring manipulation of function
+ * preambles and profiling hooks.  The synchronize_rcu_tasks() function
+ * is not (yet) intended for heavy use from multiple CPUs.
+ *
+ * Note that this guarantee implies further memory-ordering guarantees.
+ * On systems with more than one CPU, when synchronize_rcu_tasks() returns,
+ * each CPU is guaranteed to have executed a full memory barrier since the
+ * end of its last RCU-tasks read-side critical section whose beginning
+ * preceded the call to synchronize_rcu_tasks().  In addition, each CPU
+ * having an RCU-tasks read-side critical section that extends beyond
+ * the return from synchronize_rcu_tasks() is guaranteed to have executed
+ * a full memory barrier after the beginning of synchronize_rcu_tasks()
+ * and before the beginning of that RCU-tasks read-side critical section.
+ * Note that these guarantees include CPUs that are offline, idle, or
+ * executing in user mode, as well as CPUs that are executing in the kernel.
+ *
+ * Furthermore, if CPU A invoked synchronize_rcu_tasks(), which returned
+ * to its caller on CPU B, then both CPU A and CPU B are guaranteed
+ * to have executed a full memory barrier during the execution of
+ * synchronize_rcu_tasks() -- even if CPU A and CPU B are the same CPU
+ * (but again only if the system has more than one CPU).
+ */
+void synchronize_rcu_tasks(void)
+{
+	/* Complain if the scheduler has not started.  */
+	rcu_lockdep_assert(!rcu_scheduler_active,
+			   "synchronize_rcu_tasks called too soon");
+
+	/* Wait for the grace period. */
+	wait_rcu_gp(call_rcu_tasks);
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_tasks);
+
+/**
+ * rcu_barrier_tasks - Wait for in-flight call_rcu_tasks() callbacks.
+ *
+ * Although the current implementation is guaranteed to wait, it is not
+ * obligated to, for example, if there are no pending callbacks.
+ */
+void rcu_barrier_tasks(void)
+{
+	/* There is only one callback queue, so this is easy.  ;-) */
+	synchronize_rcu_tasks();
+}
+EXPORT_SYMBOL_GPL(rcu_barrier_tasks);
+
+/* See if tasks are still holding out, complain if so. */
+static void check_holdout_task(struct task_struct *t,
+			       bool needreport, bool *firstreport)
+{
+	int cpu;
+
+	if (!ACCESS_ONCE(t->rcu_tasks_holdout) ||
+	    t->rcu_tasks_nvcsw != ACCESS_ONCE(t->nvcsw) ||
+	    !ACCESS_ONCE(t->on_rq) ||
+	    (IS_ENABLED(CONFIG_NO_HZ_FULL) &&
+	     !is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) {
+		ACCESS_ONCE(t->rcu_tasks_holdout) = false;
+		list_del_init(&t->rcu_tasks_holdout_list);
+		put_task_struct(t);
+		return;
+	}
+	if (!needreport)
+		return;
+	if (*firstreport) {
+		pr_err("INFO: rcu_tasks detected stalls on tasks:\n");
+		*firstreport = false;
+	}
+	cpu = task_cpu(t);
+	pr_alert("%p: %c%c nvcsw: %lu/%lu holdout: %d idle_cpu: %d/%d\n",
+		 t, ".I"[is_idle_task(t)],
+		 "N."[cpu < 0 || !tick_nohz_full_cpu(cpu)],
+		 t->rcu_tasks_nvcsw, t->nvcsw, t->rcu_tasks_holdout,
+		 t->rcu_tasks_idle_cpu, cpu);
+	sched_show_task(t);
+}
+
+/* RCU-tasks kthread that detects grace periods and invokes callbacks. */
+static int __noreturn rcu_tasks_kthread(void *arg)
+{
+	unsigned long flags;
+	struct task_struct *g, *t;
+	unsigned long lastreport;
+	struct rcu_head *list;
+	struct rcu_head *next;
+	LIST_HEAD(rcu_tasks_holdouts);
+
+	/* FIXME: Add housekeeping affinity. */
+
+	/*
+	 * Each pass through the following loop makes one check for
+	 * newly arrived callbacks, and, if there are some, waits for
+	 * one RCU-tasks grace period and then invokes the callbacks.
+	 * This loop is terminated by the system going down.  ;-)
+	 */
+	for (;;) {
+
+		/* Pick up any new callbacks. */
+		raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags);
+		list = rcu_tasks_cbs_head;
+		rcu_tasks_cbs_head = NULL;
+		rcu_tasks_cbs_tail = &rcu_tasks_cbs_head;
+		raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags);
+
+		/* If there were none, wait a bit and start over. */
+		if (!list) {
+			wait_event_interruptible(rcu_tasks_cbs_wq,
+						 rcu_tasks_cbs_head);
+			if (!rcu_tasks_cbs_head) {
+				WARN_ON(signal_pending(current));
+				schedule_timeout_interruptible(HZ/10);
+			}
+			continue;
+		}
+
+		/*
+		 * Wait for all pre-existing t->on_rq and t->nvcsw
+		 * transitions to complete.  Invoking synchronize_sched()
+		 * suffices because all these transitions occur with
+		 * interrupts disabled.  Without this synchronize_sched(),
+		 * a read-side critical section that started before the
+		 * grace period might be incorrectly seen as having started
+		 * after the grace period.
+		 *
+		 * This synchronize_sched() also dispenses with the
+		 * need for a memory barrier on the first store to
+		 * ->rcu_tasks_holdout, as it forces the store to happen
+		 * after the beginning of the grace period.
+		 */
+		synchronize_sched();
+
+		/*
+		 * There were callbacks, so we need to wait for an
+		 * RCU-tasks grace period.  Start off by scanning
+		 * the task list for tasks that are not already
+		 * voluntarily blocked.  Mark these tasks and make
+		 * a list of them in rcu_tasks_holdouts.
+		 */
+		rcu_read_lock();
+		for_each_process_thread(g, t) {
+			if (t != current && ACCESS_ONCE(t->on_rq) &&
+			    !is_idle_task(t)) {
+				get_task_struct(t);
+				t->rcu_tasks_nvcsw = ACCESS_ONCE(t->nvcsw);
+				ACCESS_ONCE(t->rcu_tasks_holdout) = true;
+				list_add(&t->rcu_tasks_holdout_list,
+					 &rcu_tasks_holdouts);
+			}
+		}
+		rcu_read_unlock();
+
+		/*
+		 * Wait for tasks that are in the process of exiting.
+		 * This does only part of the job, ensuring that all
+		 * tasks that were previously exiting reach the point
+		 * where they have disabled preemption, allowing the
+		 * later synchronize_sched() to finish the job.
+		 */
+		synchronize_srcu(&tasks_rcu_exit_srcu);
+
+		/*
+		 * Each pass through the following loop scans the list
+		 * of holdout tasks, removing any that are no longer
+		 * holdouts.  When the list is empty, we are done.
+		 */
+		lastreport = jiffies;
+		while (!list_empty(&rcu_tasks_holdouts)) {
+			bool firstreport;
+			bool needreport;
+			int rtst;
+			struct task_struct *t1;
+
+			schedule_timeout_interruptible(HZ);
+			rtst = ACCESS_ONCE(rcu_task_stall_timeout);
+			needreport = rtst > 0 &&
+				     time_after(jiffies, lastreport + rtst);
+			if (needreport)
+				lastreport = jiffies;
+			firstreport = true;
+			WARN_ON(signal_pending(current));
+			list_for_each_entry_safe(t, t1, &rcu_tasks_holdouts,
+						rcu_tasks_holdout_list) {
+				check_holdout_task(t, needreport, &firstreport);
+				cond_resched();
+			}
+		}
+
+		/*
+		 * Because ->on_rq and ->nvcsw are not guaranteed
+		 * to have a full memory barriers prior to them in the
+		 * schedule() path, memory reordering on other CPUs could
+		 * cause their RCU-tasks read-side critical sections to
+		 * extend past the end of the grace period.  However,
+		 * because these ->nvcsw updates are carried out with
+		 * interrupts disabled, we can use synchronize_sched()
+		 * to force the needed ordering on all such CPUs.
+		 *
+		 * This synchronize_sched() also confines all
+		 * ->rcu_tasks_holdout accesses to be within the grace
+		 * period, avoiding the need for memory barriers for
+		 * ->rcu_tasks_holdout accesses.
+		 *
+		 * In addition, this synchronize_sched() waits for exiting
+		 * tasks to complete their final preempt_disable() region
+		 * of execution, cleaning up after the synchronize_srcu()
+		 * above.
+		 */
+		synchronize_sched();
+
+		/* Invoke the callbacks. */
+		while (list) {
+			next = list->next;
+			local_bh_disable();
+			list->func(list);
+			local_bh_enable();
+			list = next;
+			cond_resched();
+		}
+		schedule_timeout_uninterruptible(HZ/10);
+	}
+}
+
+/* Spawn rcu_tasks_kthread() at first call to call_rcu_tasks(). */
+static void rcu_spawn_tasks_kthread(void)
+{
+	static DEFINE_MUTEX(rcu_tasks_kthread_mutex);
+	static struct task_struct *rcu_tasks_kthread_ptr;
+	struct task_struct *t;
+
+	if (ACCESS_ONCE(rcu_tasks_kthread_ptr)) {
+		smp_mb(); /* Ensure caller sees full kthread. */
+		return;
+	}
+	mutex_lock(&rcu_tasks_kthread_mutex);
+	if (rcu_tasks_kthread_ptr) {
+		mutex_unlock(&rcu_tasks_kthread_mutex);
+		return;
+	}
+	t = kthread_run(rcu_tasks_kthread, NULL, "rcu_tasks_kthread");
+	BUG_ON(IS_ERR(t));
+	smp_mb(); /* Ensure others see full kthread. */
+	ACCESS_ONCE(rcu_tasks_kthread_ptr) = t;
+	mutex_unlock(&rcu_tasks_kthread_mutex);
+}
+
+#endif /* #ifdef CONFIG_TASKS_RCU */

kernel/softirq.c

@@ -278,7 +278,7 @@ asmlinkage __visible void __do_softirq(void)
 		pending >>= softirq_bit;
 	}
 
-	rcu_bh_qs(smp_processor_id());
+	rcu_bh_qs();
 	local_irq_disable();
 
 	pending = local_softirq_pending();

mm/mlock.c

@@ -789,7 +789,7 @@ static int do_mlockall(int flags)
 
 		/* Ignore errors */
 		mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags);
-		cond_resched();
+		cond_resched_rcu_qs();
 	}
 out:
 	return 0;

tools/testing/selftests/rcutorture/configs/rcu/CFLIST

@@ -11,3 +11,6 @@ SRCU-N
 SRCU-P
 TINY01
 TINY02
+TASKS01
+TASKS02
+TASKS03

tools/testing/selftests/rcutorture/configs/rcu/TASKS01

+CONFIG_SMP=y
+CONFIG_NR_CPUS=2
+CONFIG_HOTPLUG_CPU=y
+CONFIG_PREEMPT_NONE=n
+CONFIG_PREEMPT_VOLUNTARY=n
+CONFIG_PREEMPT=y
+CONFIG_DEBUG_LOCK_ALLOC=y
+CONFIG_PROVE_RCU=y
+CONFIG_TASKS_RCU=y

tools/testing/selftests/rcutorture/configs/rcu/TASKS01.boot

+rcutorture.torture_type=tasks

tools/testing/selftests/rcutorture/configs/rcu/TASKS02

+CONFIG_SMP=n
+CONFIG_PREEMPT_NONE=y
+CONFIG_PREEMPT_VOLUNTARY=n
+CONFIG_PREEMPT=n
+CONFIG_TASKS_RCU=y

tools/testing/selftests/rcutorture/configs/rcu/TASKS02.boot

+rcutorture.torture_type=tasks

tools/testing/selftests/rcutorture/configs/rcu/TASKS03

+CONFIG_SMP=y
+CONFIG_NR_CPUS=2
+CONFIG_HOTPLUG_CPU=n
+CONFIG_SUSPEND=n
+CONFIG_HIBERNATION=n
+CONFIG_PREEMPT_NONE=n
+CONFIG_PREEMPT_VOLUNTARY=n
+CONFIG_PREEMPT=y
+CONFIG_TASKS_RCU=y
+CONFIG_HZ_PERIODIC=n
+CONFIG_NO_HZ_IDLE=n
+CONFIG_NO_HZ_FULL=y
+CONFIG_NO_HZ_FULL_ALL=y

tools/testing/selftests/rcutorture/configs/rcu/TASKS03.boot

+rcutorture.torture_type=tasks