Merge branches 'rcu-doc.2024.02.14a', 'rcu-nocb.2024.02.14a',...

Merge branches 'rcu-doc.2024.02.14a', 'rcu-nocb.2024.02.14a', 'rcu-exp.2024.02.14a', 'rcu-tasks.2024.02.26a' and 'rcu-misc.2024.02.14a' into rcu.2024.02.26a

Documentation/admin-guide/kernel-parameters.txt

@@ -5047,6 +5047,11 @@
 			this kernel boot parameter, forcibly setting it
 			to zero.
 
+	rcutree.enable_rcu_lazy= [KNL]
+			To save power, batch RCU callbacks and flush after
+			delay, memory pressure or callback list growing too
+			big.
+
 	rcuscale.gp_async= [KNL]
 			Measure performance of asynchronous
 			grace-period primitives such as call_rcu().

include/linux/rcu_sync.h

@@ -37,7 +37,6 @@ static inline bool rcu_sync_is_idle(struct rcu_sync *rsp)
 }
 
 extern void rcu_sync_init(struct rcu_sync *);
-extern void rcu_sync_enter_start(struct rcu_sync *);
 extern void rcu_sync_enter(struct rcu_sync *);
 extern void rcu_sync_exit(struct rcu_sync *);
 extern void rcu_sync_dtor(struct rcu_sync *);

include/linux/rcupdate.h

@@ -184,9 +184,9 @@ void rcu_tasks_trace_qs_blkd(struct task_struct *t);
 	do {									\
 		int ___rttq_nesting = READ_ONCE((t)->trc_reader_nesting);	\
 										\
-		if (likely(!READ_ONCE((t)->trc_reader_special.b.need_qs)) &&	\
+		if (unlikely(READ_ONCE((t)->trc_reader_special.b.need_qs) == TRC_NEED_QS) &&	\
 		    likely(!___rttq_nesting)) {					\
-			rcu_trc_cmpxchg_need_qs((t), 0,	TRC_NEED_QS_CHECKED);	\
+			rcu_trc_cmpxchg_need_qs((t), TRC_NEED_QS, TRC_NEED_QS_CHECKED);	\
 		} else if (___rttq_nesting && ___rttq_nesting != INT_MIN &&	\
 			   !READ_ONCE((t)->trc_reader_special.b.blocked)) {	\
 			rcu_tasks_trace_qs_blkd(t);				\

include/linux/sched.h

@@ -858,6 +858,8 @@ struct task_struct {
 	u8				rcu_tasks_idx;
 	int				rcu_tasks_idle_cpu;
 	struct list_head		rcu_tasks_holdout_list;
+	int				rcu_tasks_exit_cpu;
+	struct list_head		rcu_tasks_exit_list;
 #endif /* #ifdef CONFIG_TASKS_RCU */
 
 #ifdef CONFIG_TASKS_TRACE_RCU

init/init_task.c

@@ -147,6 +147,7 @@ struct task_struct init_task __aligned(L1_CACHE_BYTES) = {
 	.rcu_tasks_holdout = false,
 	.rcu_tasks_holdout_list = LIST_HEAD_INIT(init_task.rcu_tasks_holdout_list),
 	.rcu_tasks_idle_cpu = -1,
+	.rcu_tasks_exit_list = LIST_HEAD_INIT(init_task.rcu_tasks_exit_list),
 #endif
 #ifdef CONFIG_TASKS_TRACE_RCU
 	.trc_reader_nesting = 0,

kernel/fork.c

@@ -1976,6 +1976,7 @@ static inline void rcu_copy_process(struct task_struct *p)
 	p->rcu_tasks_holdout = false;
 	INIT_LIST_HEAD(&p->rcu_tasks_holdout_list);
 	p->rcu_tasks_idle_cpu = -1;
+	INIT_LIST_HEAD(&p->rcu_tasks_exit_list);
 #endif /* #ifdef CONFIG_TASKS_RCU */
 #ifdef CONFIG_TASKS_TRACE_RCU
 	p->trc_reader_nesting = 0;

kernel/rcu/Kconfig

@@ -314,6 +314,19 @@ config RCU_LAZY
 	  To save power, batch RCU callbacks and flush after delay, memory
 	  pressure, or callback list growing too big.
 
+	  Requires rcu_nocbs=all to be set.
+
+	  Use rcutree.enable_rcu_lazy=0 to turn it off at boot time.
+
+config RCU_LAZY_DEFAULT_OFF
+	bool "Turn RCU lazy invocation off by default"
+	depends on RCU_LAZY
+	default n
+	help
+	  Allows building the kernel with CONFIG_RCU_LAZY=y yet keep it default
+	  off. Boot time param rcutree.enable_rcu_lazy=1 can be used to switch
+	  it back on.
+
 config RCU_DOUBLE_CHECK_CB_TIME
 	bool "RCU callback-batch backup time check"
 	depends on RCU_EXPERT

kernel/rcu/rcu.h

@@ -528,6 +528,12 @@ struct task_struct *get_rcu_tasks_gp_kthread(void);
 struct task_struct *get_rcu_tasks_rude_gp_kthread(void);
 #endif // # ifdef CONFIG_TASKS_RUDE_RCU
 
+#ifdef CONFIG_TASKS_RCU_GENERIC
+void tasks_cblist_init_generic(void);
+#else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
+static inline void tasks_cblist_init_generic(void) { }
+#endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */
+
 #define RCU_SCHEDULER_INACTIVE	0
 #define RCU_SCHEDULER_INIT	1
 #define RCU_SCHEDULER_RUNNING	2
@@ -543,11 +549,11 @@ enum rcutorture_type {
 };
 
 #if defined(CONFIG_RCU_LAZY)
-unsigned long rcu_lazy_get_jiffies_till_flush(void);
-void rcu_lazy_set_jiffies_till_flush(unsigned long j);
+unsigned long rcu_get_jiffies_lazy_flush(void);
+void rcu_set_jiffies_lazy_flush(unsigned long j);
 #else
-static inline unsigned long rcu_lazy_get_jiffies_till_flush(void) { return 0; }
-static inline void rcu_lazy_set_jiffies_till_flush(unsigned long j) { }
+static inline unsigned long rcu_get_jiffies_lazy_flush(void) { return 0; }
+static inline void rcu_set_jiffies_lazy_flush(unsigned long j) { }
 #endif
 
 #if defined(CONFIG_TREE_RCU)
@@ -623,12 +629,7 @@ int rcu_get_gp_kthreads_prio(void);
 void rcu_fwd_progress_check(unsigned long j);
 void rcu_force_quiescent_state(void);
 extern struct workqueue_struct *rcu_gp_wq;
-#ifdef CONFIG_RCU_EXP_KTHREAD
 extern struct kthread_worker *rcu_exp_gp_kworker;
-extern struct kthread_worker *rcu_exp_par_gp_kworker;
-#else /* !CONFIG_RCU_EXP_KTHREAD */
-extern struct workqueue_struct *rcu_par_gp_wq;
-#endif /* CONFIG_RCU_EXP_KTHREAD */
 void rcu_gp_slow_register(atomic_t *rgssp);
 void rcu_gp_slow_unregister(atomic_t *rgssp);
 #endif /* #else #ifdef CONFIG_TINY_RCU */

kernel/rcu/rcuscale.c

@@ -764,9 +764,9 @@ kfree_scale_init(void)
 
 	if (kfree_by_call_rcu) {
 		/* do a test to check the timeout. */
-		orig_jif = rcu_lazy_get_jiffies_till_flush();
+		orig_jif = rcu_get_jiffies_lazy_flush();
 
-		rcu_lazy_set_jiffies_till_flush(2 * HZ);
+		rcu_set_jiffies_lazy_flush(2 * HZ);
 		rcu_barrier();
 
 		jif_start = jiffies;
@@ -775,7 +775,7 @@ kfree_scale_init(void)
 
 		smp_cond_load_relaxed(&rcu_lazy_test1_cb_called, VAL == 1);
 
-		rcu_lazy_set_jiffies_till_flush(orig_jif);
+		rcu_set_jiffies_lazy_flush(orig_jif);
 
 		if (WARN_ON_ONCE(jiffies_at_lazy_cb - jif_start < 2 * HZ)) {
 			pr_alert("ERROR: call_rcu() CBs are not being lazy as expected!\n");

kernel/rcu/rcutorture.c

@@ -1368,9 +1368,13 @@ rcu_torture_writer(void *arg)
 	struct rcu_torture *rp;
 	struct rcu_torture *old_rp;
 	static DEFINE_TORTURE_RANDOM(rand);
+	unsigned long stallsdone = jiffies;
 	bool stutter_waited;
 	unsigned long ulo[NUM_ACTIVE_RCU_POLL_OLDSTATE];
 
+	// If a new stall test is added, this must be adjusted.
+	if (stall_cpu_holdoff + stall_gp_kthread + stall_cpu)
+		stallsdone += (stall_cpu_holdoff + stall_gp_kthread + stall_cpu + 60) * HZ;
 	VERBOSE_TOROUT_STRING("rcu_torture_writer task started");
 	if (!can_expedite)
 		pr_alert("%s" TORTURE_FLAG
@@ -1576,11 +1580,11 @@ rcu_torture_writer(void *arg)
 		    !atomic_read(&rcu_fwd_cb_nodelay) &&
 		    !cur_ops->slow_gps &&
 		    !torture_must_stop() &&
-		    boot_ended)
+		    boot_ended &&
+		    time_after(jiffies, stallsdone))
 			for (i = 0; i < ARRAY_SIZE(rcu_tortures); i++)
 				if (list_empty(&rcu_tortures[i].rtort_free) &&
-				    rcu_access_pointer(rcu_torture_current) !=
-				    &rcu_tortures[i]) {
+				    rcu_access_pointer(rcu_torture_current) != &rcu_tortures[i]) {
 					tracing_off();
 					show_rcu_gp_kthreads();
 					WARN(1, "%s: rtort_pipe_count: %d\n", __func__, rcu_tortures[i].rtort_pipe_count);
@@ -2441,7 +2445,8 @@ static struct notifier_block rcu_torture_stall_block = {
 
 /*
  * CPU-stall kthread.  It waits as specified by stall_cpu_holdoff, then
- * induces a CPU stall for the time specified by stall_cpu.
+ * induces a CPU stall for the time specified by stall_cpu.  If a new
+ * stall test is added, stallsdone in rcu_torture_writer() must be adjusted.
  */
 static int rcu_torture_stall(void *args)
 {

kernel/rcu/srcutree.c

@@ -1234,11 +1234,20 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp,
 	if (rhp)
 		rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp);
 	/*
-	 * The snapshot for acceleration must be taken _before_ the read of the
-	 * current gp sequence used for advancing, otherwise advancing may fail
-	 * and acceleration may then fail too.
+	 * It's crucial to capture the snapshot 's' for acceleration before
+	 * reading the current gp_seq that is used for advancing. This is
+	 * essential because if the acceleration snapshot is taken after a
+	 * failed advancement attempt, there's a risk that a grace period may
+	 * conclude and a new one may start in the interim. If the snapshot is
+	 * captured after this sequence of events, the acceleration snapshot 's'
+	 * could be excessively advanced, leading to acceleration failure.
+	 * In such a scenario, an 'acceleration leak' can occur, where new
+	 * callbacks become indefinitely stuck in the RCU_NEXT_TAIL segment.
+	 * Also note that encountering advancing failures is a normal
+	 * occurrence when the grace period for RCU_WAIT_TAIL is in progress.
 	 *
-	 * This could happen if:
+	 * To see this, consider the following events which occur if
+	 * rcu_seq_snap() were to be called after advance:
 	 *
 	 *  1) The RCU_WAIT_TAIL segment has callbacks (gp_num = X + 4) and the
 	 *     RCU_NEXT_READY_TAIL also has callbacks (gp_num = X + 8).
@@ -1264,6 +1273,13 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp,
 	if (rhp) {
 		rcu_segcblist_advance(&sdp->srcu_cblist,
 				      rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq));
+		/*
+		 * Acceleration can never fail because the base current gp_seq
+		 * used for acceleration is <= the value of gp_seq used for
+		 * advancing. This means that RCU_NEXT_TAIL segment will
+		 * always be able to be emptied by the acceleration into the
+		 * RCU_NEXT_READY_TAIL or RCU_WAIT_TAIL segments.
+		 */
 		WARN_ON_ONCE(!rcu_segcblist_accelerate(&sdp->srcu_cblist, s));
 	}
 	if (ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s)) {

kernel/rcu/sync.c

@@ -24,22 +24,6 @@ void rcu_sync_init(struct rcu_sync *rsp)
 	init_waitqueue_head(&rsp->gp_wait);
 }
 
-/**
- * rcu_sync_enter_start - Force readers onto slow path for multiple updates
- * @rsp: Pointer to rcu_sync structure to use for synchronization
- *
- * Must be called after rcu_sync_init() and before first use.
- *
- * Ensures rcu_sync_is_idle() returns false and rcu_sync_{enter,exit}()
- * pairs turn into NO-OPs.
- */
-void rcu_sync_enter_start(struct rcu_sync *rsp)
-{
-	rsp->gp_count++;
-	rsp->gp_state = GP_PASSED;
-}
-
-
 static void rcu_sync_func(struct rcu_head *rhp);
 
 static void rcu_sync_call(struct rcu_sync *rsp)

kernel/rcu/tasks.h

@@ -32,6 +32,7 @@ typedef void (*postgp_func_t)(struct rcu_tasks *rtp);
  * @rtp_irq_work: IRQ work queue for deferred wakeups.
  * @barrier_q_head: RCU callback for barrier operation.
  * @rtp_blkd_tasks: List of tasks blocked as readers.
+ * @rtp_exit_list: List of tasks in the latter portion of do_exit().
  * @cpu: CPU number corresponding to this entry.
  * @rtpp: Pointer to the rcu_tasks structure.
  */
@@ -46,6 +47,7 @@ struct rcu_tasks_percpu {
 	struct irq_work rtp_irq_work;
 	struct rcu_head barrier_q_head;
 	struct list_head rtp_blkd_tasks;
+	struct list_head rtp_exit_list;
 	int cpu;
 	struct rcu_tasks *rtpp;
 };
@@ -144,8 +146,6 @@ static struct rcu_tasks rt_name =							\
 }
 
 #ifdef CONFIG_TASKS_RCU
-/* Track exiting tasks in order to allow them to be waited for. */
-DEFINE_STATIC_SRCU(tasks_rcu_exit_srcu);
 
 /* Report delay in synchronize_srcu() completion in rcu_tasks_postscan(). */
 static void tasks_rcu_exit_srcu_stall(struct timer_list *unused);
@@ -240,7 +240,6 @@ static const char *tasks_gp_state_getname(struct rcu_tasks *rtp)
 static void cblist_init_generic(struct rcu_tasks *rtp)
 {
 	int cpu;
-	unsigned long flags;
 	int lim;
 	int shift;
 
@@ -266,15 +265,15 @@ static void cblist_init_generic(struct rcu_tasks *rtp)
 		WARN_ON_ONCE(!rtpcp);
 		if (cpu)
 			raw_spin_lock_init(&ACCESS_PRIVATE(rtpcp, lock));
-		local_irq_save(flags);  // serialize initialization
 		if (rcu_segcblist_empty(&rtpcp->cblist))
 			rcu_segcblist_init(&rtpcp->cblist);
-		local_irq_restore(flags);
 		INIT_WORK(&rtpcp->rtp_work, rcu_tasks_invoke_cbs_wq);
 		rtpcp->cpu = cpu;
 		rtpcp->rtpp = rtp;
 		if (!rtpcp->rtp_blkd_tasks.next)
 			INIT_LIST_HEAD(&rtpcp->rtp_blkd_tasks);
+		if (!rtpcp->rtp_exit_list.next)
+			INIT_LIST_HEAD(&rtpcp->rtp_exit_list);
 	}
 
 	pr_info("%s: Setting shift to %d and lim to %d rcu_task_cb_adjust=%d.\n", rtp->name,
@@ -851,10 +850,12 @@ static void rcu_tasks_wait_gp(struct rcu_tasks *rtp)
 //	number of voluntary context switches, and add that task to the
 //	holdout list.
 // rcu_tasks_postscan():
-//	Invoke synchronize_srcu() to ensure that all tasks that were
-//	in the process of exiting (and which thus might not know to
-//	synchronize with this RCU Tasks grace period) have completed
-//	exiting.
+//	Gather per-CPU lists of tasks in do_exit() to ensure that all
+//	tasks that were in the process of exiting (and which thus might
+//	not know to synchronize with this RCU Tasks grace period) have
+//	completed exiting.  The synchronize_rcu() in rcu_tasks_postgp()
+//	will take care of any tasks stuck in the non-preemptible region
+//	of do_exit() following its call to exit_tasks_rcu_stop().
 // check_all_holdout_tasks(), repeatedly until holdout list is empty:
 //	Scans the holdout list, attempting to identify a quiescent state
 //	for each task on the list.  If there is a quiescent state, the
@@ -867,8 +868,10 @@ static void rcu_tasks_wait_gp(struct rcu_tasks *rtp)
 //	with interrupts disabled.
 //
 // For each exiting task, the exit_tasks_rcu_start() and
-// exit_tasks_rcu_finish() functions begin and end, respectively, the SRCU
-// read-side critical sections waited for by rcu_tasks_postscan().
+// exit_tasks_rcu_finish() functions add and remove, respectively, the
+// current task to a per-CPU list of tasks that rcu_tasks_postscan() must
+// wait on.  This is necessary because rcu_tasks_postscan() must wait on
+// tasks that have already been removed from the global list of tasks.
 //
 // Pre-grace-period update-side code is ordered before the grace
 // via the raw_spin_lock.*rcu_node().  Pre-grace-period read-side code
@@ -932,9 +935,13 @@ static void rcu_tasks_pertask(struct task_struct *t, struct list_head *hop)
 	}
 }
 
+void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func);
+DEFINE_RCU_TASKS(rcu_tasks, rcu_tasks_wait_gp, call_rcu_tasks, "RCU Tasks");
+
 /* Processing between scanning taskslist and draining the holdout list. */
 static void rcu_tasks_postscan(struct list_head *hop)
 {
+	int cpu;
 	int rtsi = READ_ONCE(rcu_task_stall_info);
 
 	if (!IS_ENABLED(CONFIG_TINY_RCU)) {
@@ -948,9 +955,9 @@ static void rcu_tasks_postscan(struct list_head *hop)
 	 * this, divide the fragile exit path part in two intersecting
 	 * read side critical sections:
 	 *
-	 * 1) An _SRCU_ read side starting before calling exit_notify(),
-	 *    which may remove the task from the tasklist, and ending after
-	 *    the final preempt_disable() call in do_exit().
+	 * 1) A task_struct list addition before calling exit_notify(),
+	 *    which may remove the task from the tasklist, with the
+	 *    removal after the final preempt_disable() call in do_exit().
 	 *
 	 * 2) An _RCU_ read side starting with the final preempt_disable()
 	 *    call in do_exit() and ending with the final call to schedule()
@@ -959,7 +966,37 @@ static void rcu_tasks_postscan(struct list_head *hop)
 	 * This handles the part 1). And postgp will handle part 2) with a
 	 * call to synchronize_rcu().
 	 */
-	synchronize_srcu(&tasks_rcu_exit_srcu);
+
+	for_each_possible_cpu(cpu) {
+		unsigned long j = jiffies + 1;
+		struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rcu_tasks.rtpcpu, cpu);
+		struct task_struct *t;
+		struct task_struct *t1;
+		struct list_head tmp;
+
+		raw_spin_lock_irq_rcu_node(rtpcp);
+		list_for_each_entry_safe(t, t1, &rtpcp->rtp_exit_list, rcu_tasks_exit_list) {
+			if (list_empty(&t->rcu_tasks_holdout_list))
+				rcu_tasks_pertask(t, hop);
+
+			// RT kernels need frequent pauses, otherwise
+			// pause at least once per pair of jiffies.
+			if (!IS_ENABLED(CONFIG_PREEMPT_RT) && time_before(jiffies, j))
+				continue;
+
+			// Keep our place in the list while pausing.
+			// Nothing else traverses this list, so adding a
+			// bare list_head is OK.
+			list_add(&tmp, &t->rcu_tasks_exit_list);
+			raw_spin_unlock_irq_rcu_node(rtpcp);
+			cond_resched(); // For CONFIG_PREEMPT=n kernels
+			raw_spin_lock_irq_rcu_node(rtpcp);
+			t1 = list_entry(tmp.next, struct task_struct, rcu_tasks_exit_list);
+			list_del(&tmp);
+			j = jiffies + 1;
+		}
+		raw_spin_unlock_irq_rcu_node(rtpcp);
+	}
 
 	if (!IS_ENABLED(CONFIG_TINY_RCU))
 		del_timer_sync(&tasks_rcu_exit_srcu_stall_timer);
@@ -1027,7 +1064,6 @@ static void rcu_tasks_postgp(struct rcu_tasks *rtp)
 	 *
 	 * In addition, this synchronize_rcu() waits for exiting tasks
 	 * to complete their final preempt_disable() region of execution,
-	 * cleaning up after synchronize_srcu(&tasks_rcu_exit_srcu),
 	 * enforcing the whole region before tasklist removal until
 	 * the final schedule() with TASK_DEAD state to be an RCU TASKS
 	 * read side critical section.
@@ -1035,9 +1071,6 @@ static void rcu_tasks_postgp(struct rcu_tasks *rtp)
 	synchronize_rcu();
 }
 
-void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func);
-DEFINE_RCU_TASKS(rcu_tasks, rcu_tasks_wait_gp, call_rcu_tasks, "RCU Tasks");
-
 static void tasks_rcu_exit_srcu_stall(struct timer_list *unused)
 {
 #ifndef CONFIG_TINY_RCU
@@ -1118,7 +1151,6 @@ module_param(rcu_tasks_lazy_ms, int, 0444);
 
 static int __init rcu_spawn_tasks_kthread(void)
 {
-	cblist_init_generic(&rcu_tasks);
 	rcu_tasks.gp_sleep = HZ / 10;
 	rcu_tasks.init_fract = HZ / 10;
 	if (rcu_tasks_lazy_ms >= 0)
@@ -1147,25 +1179,48 @@ struct task_struct *get_rcu_tasks_gp_kthread(void)
 EXPORT_SYMBOL_GPL(get_rcu_tasks_gp_kthread);
 
 /*
- * Contribute to protect against tasklist scan blind spot while the
- * task is exiting and may be removed from the tasklist. See
- * corresponding synchronize_srcu() for further details.
+ * Protect against tasklist scan blind spot while the task is exiting and
+ * may be removed from the tasklist.  Do this by adding the task to yet
+ * another list.
+ *
+ * Note that the task will remove itself from this list, so there is no
+ * need for get_task_struct(), except in the case where rcu_tasks_pertask()
+ * adds it to the holdout list, in which case rcu_tasks_pertask() supplies
+ * the needed get_task_struct().
  */
-void exit_tasks_rcu_start(void) __acquires(&tasks_rcu_exit_srcu)
+void exit_tasks_rcu_start(void)
 {
-	current->rcu_tasks_idx = __srcu_read_lock(&tasks_rcu_exit_srcu);
+	unsigned long flags;
+	struct rcu_tasks_percpu *rtpcp;
+	struct task_struct *t = current;
+
+	WARN_ON_ONCE(!list_empty(&t->rcu_tasks_exit_list));
+	preempt_disable();
+	rtpcp = this_cpu_ptr(rcu_tasks.rtpcpu);
+	t->rcu_tasks_exit_cpu = smp_processor_id();
+	raw_spin_lock_irqsave_rcu_node(rtpcp, flags);
+	if (!rtpcp->rtp_exit_list.next)
+		INIT_LIST_HEAD(&rtpcp->rtp_exit_list);
+	list_add(&t->rcu_tasks_exit_list, &rtpcp->rtp_exit_list);
+	raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
+	preempt_enable();
 }
 
 /*
- * Contribute to protect against tasklist scan blind spot while the
- * task is exiting and may be removed from the tasklist. See
- * corresponding synchronize_srcu() for further details.
+ * Remove the task from the "yet another list" because do_exit() is now
+ * non-preemptible, allowing synchronize_rcu() to wait beyond this point.
  */
-void exit_tasks_rcu_stop(void) __releases(&tasks_rcu_exit_srcu)
+void exit_tasks_rcu_stop(void)
 {
+	unsigned long flags;
+	struct rcu_tasks_percpu *rtpcp;
 	struct task_struct *t = current;
 
-	__srcu_read_unlock(&tasks_rcu_exit_srcu, t->rcu_tasks_idx);
+	WARN_ON_ONCE(list_empty(&t->rcu_tasks_exit_list));
+	rtpcp = per_cpu_ptr(rcu_tasks.rtpcpu, t->rcu_tasks_exit_cpu);
+	raw_spin_lock_irqsave_rcu_node(rtpcp, flags);
+	list_del_init(&t->rcu_tasks_exit_list);
+	raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
 }
 
 /*
@@ -1282,7 +1337,6 @@ module_param(rcu_tasks_rude_lazy_ms, int, 0444);
 
 static int __init rcu_spawn_tasks_rude_kthread(void)
 {
-	cblist_init_generic(&rcu_tasks_rude);
 	rcu_tasks_rude.gp_sleep = HZ / 10;
 	if (rcu_tasks_rude_lazy_ms >= 0)
 		rcu_tasks_rude.lazy_jiffies = msecs_to_jiffies(rcu_tasks_rude_lazy_ms);
@@ -1914,7 +1968,6 @@ module_param(rcu_tasks_trace_lazy_ms, int, 0444);
 
 static int __init rcu_spawn_tasks_trace_kthread(void)
 {
-	cblist_init_generic(&rcu_tasks_trace);
 	if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) {
 		rcu_tasks_trace.gp_sleep = HZ / 10;
 		rcu_tasks_trace.init_fract = HZ / 10;
@@ -2086,6 +2139,24 @@ late_initcall(rcu_tasks_verify_schedule_work);
 static void rcu_tasks_initiate_self_tests(void) { }
 #endif /* #else #ifdef CONFIG_PROVE_RCU */
 
+void __init tasks_cblist_init_generic(void)
+{
+	lockdep_assert_irqs_disabled();
+	WARN_ON(num_online_cpus() > 1);
+
+#ifdef CONFIG_TASKS_RCU
+	cblist_init_generic(&rcu_tasks);
+#endif
+
+#ifdef CONFIG_TASKS_RUDE_RCU
+	cblist_init_generic(&rcu_tasks_rude);
+#endif
+
+#ifdef CONFIG_TASKS_TRACE_RCU
+	cblist_init_generic(&rcu_tasks_trace);
+#endif
+}
+
 void __init rcu_init_tasks_generic(void)
 {
 #ifdef CONFIG_TASKS_RCU

kernel/rcu/tiny.c

@@ -261,4 +261,5 @@ void __init rcu_init(void)
 {
 	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
 	rcu_early_boot_tests();
+	tasks_cblist_init_generic();
 }

kernel/rcu/tree.c

@@ -145,7 +145,7 @@ static int rcu_scheduler_fully_active __read_mostly;
 
 static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp,
 			      unsigned long gps, unsigned long flags);
-static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
+static struct task_struct *rcu_boost_task(struct rcu_node *rnp);
 static void invoke_rcu_core(void);
 static void rcu_report_exp_rdp(struct rcu_data *rdp);
 static void sync_sched_exp_online_cleanup(int cpu);
@@ -2145,6 +2145,12 @@ static void rcu_do_batch(struct rcu_data *rdp)
 	 * Extract the list of ready callbacks, disabling IRQs to prevent
 	 * races with call_rcu() from interrupt handlers.  Leave the
 	 * callback counts, as rcu_barrier() needs to be conservative.
+	 *
+	 * Callbacks execution is fully ordered against preceding grace period
+	 * completion (materialized by rnp->gp_seq update) thanks to the
+	 * smp_mb__after_unlock_lock() upon node locking required for callbacks
+	 * advancing. In NOCB mode this ordering is then further relayed through
+	 * the nocb locking that protects both callbacks advancing and extraction.
 	 */
 	rcu_nocb_lock_irqsave(rdp, flags);
 	WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
@@ -2591,12 +2597,26 @@ static int __init rcu_spawn_core_kthreads(void)
 	return 0;
 }
 
+static void rcutree_enqueue(struct rcu_data *rdp, struct rcu_head *head, rcu_callback_t func)
+{
+	rcu_segcblist_enqueue(&rdp->cblist, head);
+	if (__is_kvfree_rcu_offset((unsigned long)func))
+		trace_rcu_kvfree_callback(rcu_state.name, head,
+					 (unsigned long)func,
+					 rcu_segcblist_n_cbs(&rdp->cblist));
+	else
+		trace_rcu_callback(rcu_state.name, head,
+				   rcu_segcblist_n_cbs(&rdp->cblist));
+	trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCBQueued"));
+}
+
 /*
  * Handle any core-RCU processing required by a call_rcu() invocation.
  */
-static void __call_rcu_core(struct rcu_data *rdp, struct rcu_head *head,
-			    unsigned long flags)
+static void call_rcu_core(struct rcu_data *rdp, struct rcu_head *head,
+			  rcu_callback_t func, unsigned long flags)
 {
+	rcutree_enqueue(rdp, head, func);
 	/*
 	 * If called from an extended quiescent state, invoke the RCU
 	 * core in order to force a re-evaluation of RCU's idleness.
@@ -2692,7 +2712,6 @@ __call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy_in)
 	unsigned long flags;
 	bool lazy;
 	struct rcu_data *rdp;
-	bool was_alldone;
 
 	/* Misaligned rcu_head! */
 	WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));
@@ -2729,30 +2748,18 @@ __call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy_in)
 	}
 
 	check_cb_ovld(rdp);
-	if (rcu_nocb_try_bypass(rdp, head, &was_alldone, flags, lazy))
-		return; // Enqueued onto ->nocb_bypass, so just leave.
-	// If no-CBs CPU gets here, rcu_nocb_try_bypass() acquired ->nocb_lock.
-	rcu_segcblist_enqueue(&rdp->cblist, head);
-	if (__is_kvfree_rcu_offset((unsigned long)func))
-		trace_rcu_kvfree_callback(rcu_state.name, head,
-					 (unsigned long)func,
-					 rcu_segcblist_n_cbs(&rdp->cblist));
-	else
-		trace_rcu_callback(rcu_state.name, head,
-				   rcu_segcblist_n_cbs(&rdp->cblist));
 
-	trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCBQueued"));
-
-	/* Go handle any RCU core processing required. */
-	if (unlikely(rcu_rdp_is_offloaded(rdp))) {
-		__call_rcu_nocb_wake(rdp, was_alldone, flags); /* unlocks */
-	} else {
-		__call_rcu_core(rdp, head, flags);
-		local_irq_restore(flags);
-	}
+	if (unlikely(rcu_rdp_is_offloaded(rdp)))
+		call_rcu_nocb(rdp, head, func, flags, lazy);
+	else
+		call_rcu_core(rdp, head, func, flags);
+	local_irq_restore(flags);
 }
 
 #ifdef CONFIG_RCU_LAZY
+static bool enable_rcu_lazy __read_mostly = !IS_ENABLED(CONFIG_RCU_LAZY_DEFAULT_OFF);
+module_param(enable_rcu_lazy, bool, 0444);
+
 /**
  * call_rcu_hurry() - Queue RCU callback for invocation after grace period, and
  * flush all lazy callbacks (including the new one) to the main ->cblist while
@@ -2778,6 +2785,8 @@ void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func)
 	__call_rcu_common(head, func, false);
 }
 EXPORT_SYMBOL_GPL(call_rcu_hurry);
+#else
+#define enable_rcu_lazy		false
 #endif
 
 /**
@@ -2826,7 +2835,7 @@ EXPORT_SYMBOL_GPL(call_rcu_hurry);
  */
 void call_rcu(struct rcu_head *head, rcu_callback_t func)
 {
-	__call_rcu_common(head, func, IS_ENABLED(CONFIG_RCU_LAZY));
+	__call_rcu_common(head, func, enable_rcu_lazy);
 }
 EXPORT_SYMBOL_GPL(call_rcu);
 
@@ -4394,6 +4403,66 @@ rcu_boot_init_percpu_data(int cpu)
 	rcu_boot_init_nocb_percpu_data(rdp);
 }
 
+struct kthread_worker *rcu_exp_gp_kworker;
+
+static void rcu_spawn_exp_par_gp_kworker(struct rcu_node *rnp)
+{
+	struct kthread_worker *kworker;
+	const char *name = "rcu_exp_par_gp_kthread_worker/%d";
+	struct sched_param param = { .sched_priority = kthread_prio };
+	int rnp_index = rnp - rcu_get_root();
+
+	if (rnp->exp_kworker)
+		return;
+
+	kworker = kthread_create_worker(0, name, rnp_index);
+	if (IS_ERR_OR_NULL(kworker)) {
+		pr_err("Failed to create par gp kworker on %d/%d\n",
+		       rnp->grplo, rnp->grphi);
+		return;
+	}
+	WRITE_ONCE(rnp->exp_kworker, kworker);
+
+	if (IS_ENABLED(CONFIG_RCU_EXP_KTHREAD))
+		sched_setscheduler_nocheck(kworker->task, SCHED_FIFO, &param);
+}
+
+static struct task_struct *rcu_exp_par_gp_task(struct rcu_node *rnp)
+{
+	struct kthread_worker *kworker = READ_ONCE(rnp->exp_kworker);
+
+	if (!kworker)
+		return NULL;
+
+	return kworker->task;
+}
+
+static void __init rcu_start_exp_gp_kworker(void)
+{
+	const char *name = "rcu_exp_gp_kthread_worker";
+	struct sched_param param = { .sched_priority = kthread_prio };
+
+	rcu_exp_gp_kworker = kthread_create_worker(0, name);
+	if (IS_ERR_OR_NULL(rcu_exp_gp_kworker)) {
+		pr_err("Failed to create %s!\n", name);
+		rcu_exp_gp_kworker = NULL;
+		return;
+	}
+
+	if (IS_ENABLED(CONFIG_RCU_EXP_KTHREAD))
+		sched_setscheduler_nocheck(rcu_exp_gp_kworker->task, SCHED_FIFO, &param);
+}
+
+static void rcu_spawn_rnp_kthreads(struct rcu_node *rnp)
+{
+	if (rcu_scheduler_fully_active) {
+		mutex_lock(&rnp->kthread_mutex);
+		rcu_spawn_one_boost_kthread(rnp);
+		rcu_spawn_exp_par_gp_kworker(rnp);
+		mutex_unlock(&rnp->kthread_mutex);
+	}
+}
+
 /*
  * Invoked early in the CPU-online process, when pretty much all services
  * are available.  The incoming CPU is not present.
@@ -4442,7 +4511,7 @@ int rcutree_prepare_cpu(unsigned int cpu)
 	rdp->rcu_iw_gp_seq = rdp->gp_seq - 1;
 	trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuonl"));
 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-	rcu_spawn_one_boost_kthread(rnp);
+	rcu_spawn_rnp_kthreads(rnp);
 	rcu_spawn_cpu_nocb_kthread(cpu);
 	WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus + 1);
 
@@ -4450,13 +4519,64 @@ int rcutree_prepare_cpu(unsigned int cpu)
 }
 
 /*
- * Update RCU priority boot kthread affinity for CPU-hotplug changes.
+ * Update kthreads affinity during CPU-hotplug changes.
+ *
+ * Set the per-rcu_node kthread's affinity to cover all CPUs that are
+ * served by the rcu_node in question.  The CPU hotplug lock is still
+ * held, so the value of rnp->qsmaskinit will be stable.
+ *
+ * We don't include outgoingcpu in the affinity set, use -1 if there is
+ * no outgoing CPU.  If there are no CPUs left in the affinity set,
+ * this function allows the kthread to execute on any CPU.
+ *
+ * Any future concurrent calls are serialized via ->kthread_mutex.
  */
-static void rcutree_affinity_setting(unsigned int cpu, int outgoing)
+static void rcutree_affinity_setting(unsigned int cpu, int outgoingcpu)
 {
-	struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+	cpumask_var_t cm;
+	unsigned long mask;
+	struct rcu_data *rdp;
+	struct rcu_node *rnp;
+	struct task_struct *task_boost, *task_exp;
+
+	rdp = per_cpu_ptr(&rcu_data, cpu);
+	rnp = rdp->mynode;
+
+	task_boost = rcu_boost_task(rnp);
+	task_exp = rcu_exp_par_gp_task(rnp);
+
+	/*
+	 * If CPU is the boot one, those tasks are created later from early
+	 * initcall since kthreadd must be created first.
+	 */
+	if (!task_boost && !task_exp)
+		return;
+
+	if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
+		return;
+
+	mutex_lock(&rnp->kthread_mutex);
+	mask = rcu_rnp_online_cpus(rnp);
+	for_each_leaf_node_possible_cpu(rnp, cpu)
+		if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
+		    cpu != outgoingcpu)
+			cpumask_set_cpu(cpu, cm);
+	cpumask_and(cm, cm, housekeeping_cpumask(HK_TYPE_RCU));
+	if (cpumask_empty(cm)) {
+		cpumask_copy(cm, housekeeping_cpumask(HK_TYPE_RCU));
+		if (outgoingcpu >= 0)
+			cpumask_clear_cpu(outgoingcpu, cm);
+	}
+
+	if (task_exp)
+		set_cpus_allowed_ptr(task_exp, cm);
+
+	if (task_boost)
+		set_cpus_allowed_ptr(task_boost, cm);
 
-	rcu_boost_kthread_setaffinity(rdp->mynode, outgoing);
+	mutex_unlock(&rnp->kthread_mutex);
+
+	free_cpumask_var(cm);
 }
 
 /*
@@ -4640,8 +4760,9 @@ void rcutree_migrate_callbacks(int cpu)
 		__call_rcu_nocb_wake(my_rdp, true, flags);
 	} else {
 		rcu_nocb_unlock(my_rdp); /* irqs remain disabled. */
-		raw_spin_unlock_irqrestore_rcu_node(my_rnp, flags);
+		raw_spin_unlock_rcu_node(my_rnp); /* irqs remain disabled. */
 	}
+	local_irq_restore(flags);
 	if (needwake)
 		rcu_gp_kthread_wake();
 	lockdep_assert_irqs_enabled();
@@ -4730,51 +4851,6 @@ static int rcu_pm_notify(struct notifier_block *self,
 	return NOTIFY_OK;
 }
 
-#ifdef CONFIG_RCU_EXP_KTHREAD
-struct kthread_worker *rcu_exp_gp_kworker;
-struct kthread_worker *rcu_exp_par_gp_kworker;
-
-static void __init rcu_start_exp_gp_kworkers(void)
-{
-	const char *par_gp_kworker_name = "rcu_exp_par_gp_kthread_worker";
-	const char *gp_kworker_name = "rcu_exp_gp_kthread_worker";
-	struct sched_param param = { .sched_priority = kthread_prio };
-
-	rcu_exp_gp_kworker = kthread_create_worker(0, gp_kworker_name);
-	if (IS_ERR_OR_NULL(rcu_exp_gp_kworker)) {
-		pr_err("Failed to create %s!\n", gp_kworker_name);
-		return;
-	}
-
-	rcu_exp_par_gp_kworker = kthread_create_worker(0, par_gp_kworker_name);
-	if (IS_ERR_OR_NULL(rcu_exp_par_gp_kworker)) {
-		pr_err("Failed to create %s!\n", par_gp_kworker_name);
-		kthread_destroy_worker(rcu_exp_gp_kworker);
-		return;
-	}
-
-	sched_setscheduler_nocheck(rcu_exp_gp_kworker->task, SCHED_FIFO, &param);
-	sched_setscheduler_nocheck(rcu_exp_par_gp_kworker->task, SCHED_FIFO,
-				   &param);
-}
-
-static inline void rcu_alloc_par_gp_wq(void)
-{
-}
-#else /* !CONFIG_RCU_EXP_KTHREAD */
-struct workqueue_struct *rcu_par_gp_wq;
-
-static void __init rcu_start_exp_gp_kworkers(void)
-{
-}
-
-static inline void rcu_alloc_par_gp_wq(void)
-{
-	rcu_par_gp_wq = alloc_workqueue("rcu_par_gp", WQ_MEM_RECLAIM, 0);
-	WARN_ON(!rcu_par_gp_wq);
-}
-#endif /* CONFIG_RCU_EXP_KTHREAD */
-
 /*
  * Spawn the kthreads that handle RCU's grace periods.
  */
@@ -4809,10 +4885,10 @@ static int __init rcu_spawn_gp_kthread(void)
 	 * due to rcu_scheduler_fully_active.
 	 */
 	rcu_spawn_cpu_nocb_kthread(smp_processor_id());
-	rcu_spawn_one_boost_kthread(rdp->mynode);
+	rcu_spawn_rnp_kthreads(rdp->mynode);
 	rcu_spawn_core_kthreads();
 	/* Create kthread worker for expedited GPs */
-	rcu_start_exp_gp_kworkers();
+	rcu_start_exp_gp_kworker();
 	return 0;
 }
 early_initcall(rcu_spawn_gp_kthread);
@@ -4915,7 +4991,7 @@ static void __init rcu_init_one(void)
 			init_waitqueue_head(&rnp->exp_wq[2]);
 			init_waitqueue_head(&rnp->exp_wq[3]);
 			spin_lock_init(&rnp->exp_lock);
-			mutex_init(&rnp->boost_kthread_mutex);
+			mutex_init(&rnp->kthread_mutex);
 			raw_spin_lock_init(&rnp->exp_poll_lock);
 			rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED;
 			INIT_WORK(&rnp->exp_poll_wq, sync_rcu_do_polled_gp);
@@ -5152,7 +5228,6 @@ void __init rcu_init(void)
 	/* Create workqueue for Tree SRCU and for expedited GPs. */
 	rcu_gp_wq = alloc_workqueue("rcu_gp", WQ_MEM_RECLAIM, 0);
 	WARN_ON(!rcu_gp_wq);
-	rcu_alloc_par_gp_wq();
 
 	/* Fill in default value for rcutree.qovld boot parameter. */
 	/* -After- the rcu_node ->lock fields are initialized! */
@@ -5165,6 +5240,8 @@ void __init rcu_init(void)
 	(void)start_poll_synchronize_rcu_expedited();
 
 	rcu_test_sync_prims();
+
+	tasks_cblist_init_generic();
 }
 
 #include "tree_stall.h"

kernel/rcu/tree.h

@@ -21,14 +21,10 @@
 
 #include "rcu_segcblist.h"
 
-/* Communicate arguments to a workqueue handler. */
+/* Communicate arguments to a kthread worker handler. */
 struct rcu_exp_work {
 	unsigned long rew_s;
-#ifdef CONFIG_RCU_EXP_KTHREAD
 	struct kthread_work rew_work;
-#else
-	struct work_struct rew_work;
-#endif /* CONFIG_RCU_EXP_KTHREAD */
 };
 
 /* RCU's kthread states for tracing. */
@@ -72,6 +68,9 @@ struct rcu_node {
 				/* Online CPUs for next expedited GP. */
 				/*  Any CPU that has ever been online will */
 				/*  have its bit set. */
+	struct kthread_worker *exp_kworker;
+				/* Workers performing per node expedited GP */
+				/* initialization. */
 	unsigned long cbovldmask;
 				/* CPUs experiencing callback overload. */
 	unsigned long ffmask;	/* Fully functional CPUs. */
@@ -113,7 +112,7 @@ struct rcu_node {
 				/*  side effect, not as a lock. */
 	unsigned long boost_time;
 				/* When to start boosting (jiffies). */
-	struct mutex boost_kthread_mutex;
+	struct mutex kthread_mutex;
 				/* Exclusion for thread spawning and affinity */
 				/*  manipulation. */
 	struct task_struct *boost_kthread_task;
@@ -467,11 +466,10 @@ static void rcu_init_one_nocb(struct rcu_node *rnp);
 static bool wake_nocb_gp(struct rcu_data *rdp, bool force);
 static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
 				  unsigned long j, bool lazy);
-static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
-				bool *was_alldone, unsigned long flags,
-				bool lazy);
-static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty,
-				 unsigned long flags);
+static void call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *head,
+			  rcu_callback_t func, unsigned long flags, bool lazy);
+static void __maybe_unused __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty,
+						unsigned long flags);
 static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level);
 static bool do_nocb_deferred_wakeup(struct rcu_data *rdp);
 static void rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp);

kernel/rcu/tree_exp.h

@@ -198,10 +198,9 @@ static void __rcu_report_exp_rnp(struct rcu_node *rnp,
 		}
 		if (rnp->parent == NULL) {
 			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-			if (wake) {
-				smp_mb(); /* EGP done before wake_up(). */
+			if (wake)
 				swake_up_one_online(&rcu_state.expedited_wq);
-			}
+
 			break;
 		}
 		mask = rnp->grpmask;
@@ -419,7 +418,6 @@ static void __sync_rcu_exp_select_node_cpus(struct rcu_exp_work *rewp)
 
 static void rcu_exp_sel_wait_wake(unsigned long s);
 
-#ifdef CONFIG_RCU_EXP_KTHREAD
 static void sync_rcu_exp_select_node_cpus(struct kthread_work *wp)
 {
 	struct rcu_exp_work *rewp =
@@ -428,9 +426,14 @@ static void sync_rcu_exp_select_node_cpus(struct kthread_work *wp)
 	__sync_rcu_exp_select_node_cpus(rewp);
 }
 
-static inline bool rcu_gp_par_worker_started(void)
+static inline bool rcu_exp_worker_started(void)
+{
+	return !!READ_ONCE(rcu_exp_gp_kworker);
+}
+
+static inline bool rcu_exp_par_worker_started(struct rcu_node *rnp)
 {
-	return !!READ_ONCE(rcu_exp_par_gp_kworker);
+	return !!READ_ONCE(rnp->exp_kworker);
 }
 
 static inline void sync_rcu_exp_select_cpus_queue_work(struct rcu_node *rnp)
@@ -441,7 +444,7 @@ static inline void sync_rcu_exp_select_cpus_queue_work(struct rcu_node *rnp)
 	 * another work item on the same kthread worker can result in
 	 * deadlock.
 	 */
-	kthread_queue_work(rcu_exp_par_gp_kworker, &rnp->rew.rew_work);
+	kthread_queue_work(READ_ONCE(rnp->exp_kworker), &rnp->rew.rew_work);
 }
 
 static inline void sync_rcu_exp_select_cpus_flush_work(struct rcu_node *rnp)
@@ -466,64 +469,6 @@ static inline void synchronize_rcu_expedited_queue_work(struct rcu_exp_work *rew
 	kthread_queue_work(rcu_exp_gp_kworker, &rew->rew_work);
 }
 
-static inline void synchronize_rcu_expedited_destroy_work(struct rcu_exp_work *rew)
-{
-}
-#else /* !CONFIG_RCU_EXP_KTHREAD */
-static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
-{
-	struct rcu_exp_work *rewp =
-		container_of(wp, struct rcu_exp_work, rew_work);
-
-	__sync_rcu_exp_select_node_cpus(rewp);
-}
-
-static inline bool rcu_gp_par_worker_started(void)
-{
-	return !!READ_ONCE(rcu_par_gp_wq);
-}
-
-static inline void sync_rcu_exp_select_cpus_queue_work(struct rcu_node *rnp)
-{
-	int cpu = find_next_bit(&rnp->ffmask, BITS_PER_LONG, -1);
-
-	INIT_WORK(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus);
-	/* If all offline, queue the work on an unbound CPU. */
-	if (unlikely(cpu > rnp->grphi - rnp->grplo))
-		cpu = WORK_CPU_UNBOUND;
-	else
-		cpu += rnp->grplo;
-	queue_work_on(cpu, rcu_par_gp_wq, &rnp->rew.rew_work);
-}
-
-static inline void sync_rcu_exp_select_cpus_flush_work(struct rcu_node *rnp)
-{
-	flush_work(&rnp->rew.rew_work);
-}
-
-/*
- * Work-queue handler to drive an expedited grace period forward.
- */
-static void wait_rcu_exp_gp(struct work_struct *wp)
-{
-	struct rcu_exp_work *rewp;
-
-	rewp = container_of(wp, struct rcu_exp_work, rew_work);
-	rcu_exp_sel_wait_wake(rewp->rew_s);
-}
-
-static inline void synchronize_rcu_expedited_queue_work(struct rcu_exp_work *rew)
-{
-	INIT_WORK_ONSTACK(&rew->rew_work, wait_rcu_exp_gp);
-	queue_work(rcu_gp_wq, &rew->rew_work);
-}
-
-static inline void synchronize_rcu_expedited_destroy_work(struct rcu_exp_work *rew)
-{
-	destroy_work_on_stack(&rew->rew_work);
-}
-#endif /* CONFIG_RCU_EXP_KTHREAD */
-
 /*
  * Select the nodes that the upcoming expedited grace period needs
  * to wait for.
@@ -541,7 +486,7 @@ static void sync_rcu_exp_select_cpus(void)
 		rnp->exp_need_flush = false;
 		if (!READ_ONCE(rnp->expmask))
 			continue; /* Avoid early boot non-existent wq. */
-		if (!rcu_gp_par_worker_started() ||
+		if (!rcu_exp_par_worker_started(rnp) ||
 		    rcu_scheduler_active != RCU_SCHEDULER_RUNNING ||
 		    rcu_is_last_leaf_node(rnp)) {
 			/* No worker started yet or last leaf, do direct call. */
@@ -956,7 +901,6 @@ static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp)
  */
 void synchronize_rcu_expedited(void)
 {
-	bool boottime = (rcu_scheduler_active == RCU_SCHEDULER_INIT);
 	unsigned long flags;
 	struct rcu_exp_work rew;
 	struct rcu_node *rnp;
@@ -996,7 +940,7 @@ void synchronize_rcu_expedited(void)
 		return;  /* Someone else did our work for us. */
 
 	/* Ensure that load happens before action based on it. */
-	if (unlikely(boottime)) {
+	if (unlikely((rcu_scheduler_active == RCU_SCHEDULER_INIT) || !rcu_exp_worker_started())) {
 		/* Direct call during scheduler init and early_initcalls(). */
 		rcu_exp_sel_wait_wake(s);
 	} else {
@@ -1013,9 +957,6 @@ void synchronize_rcu_expedited(void)
 
 	/* Let the next expedited grace period start. */
 	mutex_unlock(&rcu_state.exp_mutex);
-
-	if (likely(!boottime))
-		synchronize_rcu_expedited_destroy_work(&rew);
 }
 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
 

kernel/rcu/tree_nocb.h

@@ -256,6 +256,7 @@ static bool wake_nocb_gp(struct rcu_data *rdp, bool force)
 	return __wake_nocb_gp(rdp_gp, rdp, force, flags);
 }
 
+#ifdef CONFIG_RCU_LAZY
 /*
  * LAZY_FLUSH_JIFFIES decides the maximum amount of time that
  * can elapse before lazy callbacks are flushed. Lazy callbacks
@@ -264,21 +265,20 @@ static bool wake_nocb_gp(struct rcu_data *rdp, bool force)
  * left unsubmitted to RCU after those many jiffies.
  */
 #define LAZY_FLUSH_JIFFIES (10 * HZ)
-static unsigned long jiffies_till_flush = LAZY_FLUSH_JIFFIES;
+static unsigned long jiffies_lazy_flush = LAZY_FLUSH_JIFFIES;
 
-#ifdef CONFIG_RCU_LAZY
 // To be called only from test code.
-void rcu_lazy_set_jiffies_till_flush(unsigned long jif)
+void rcu_set_jiffies_lazy_flush(unsigned long jif)
 {
-	jiffies_till_flush = jif;
+	jiffies_lazy_flush = jif;
 }
-EXPORT_SYMBOL(rcu_lazy_set_jiffies_till_flush);
+EXPORT_SYMBOL(rcu_set_jiffies_lazy_flush);
 
-unsigned long rcu_lazy_get_jiffies_till_flush(void)
+unsigned long rcu_get_jiffies_lazy_flush(void)
 {
-	return jiffies_till_flush;
+	return jiffies_lazy_flush;
 }
-EXPORT_SYMBOL(rcu_lazy_get_jiffies_till_flush);
+EXPORT_SYMBOL(rcu_get_jiffies_lazy_flush);
 #endif
 
 /*
@@ -299,7 +299,7 @@ static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype,
 	 */
 	if (waketype == RCU_NOCB_WAKE_LAZY &&
 	    rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT) {
-		mod_timer(&rdp_gp->nocb_timer, jiffies + jiffies_till_flush);
+		mod_timer(&rdp_gp->nocb_timer, jiffies + rcu_get_jiffies_lazy_flush());
 		WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype);
 	} else if (waketype == RCU_NOCB_WAKE_BYPASS) {
 		mod_timer(&rdp_gp->nocb_timer, jiffies + 2);
@@ -482,7 +482,7 @@ static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
 	// flush ->nocb_bypass to ->cblist.
 	if ((ncbs && !bypass_is_lazy && j != READ_ONCE(rdp->nocb_bypass_first)) ||
 	    (ncbs &&  bypass_is_lazy &&
-	     (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + jiffies_till_flush))) ||
+	     (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + rcu_get_jiffies_lazy_flush()))) ||
 	    ncbs >= qhimark) {
 		rcu_nocb_lock(rdp);
 		*was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
@@ -532,9 +532,7 @@ static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
 	// 2. Both of these conditions are met:
 	//    a. The bypass list previously had only lazy CBs, and:
 	//    b. The new CB is non-lazy.
-	if (ncbs && (!bypass_is_lazy || lazy)) {
-		local_irq_restore(flags);
-	} else {
+	if (!ncbs || (bypass_is_lazy && !lazy)) {
 		// No-CBs GP kthread might be indefinitely asleep, if so, wake.
 		rcu_nocb_lock(rdp); // Rare during call_rcu() flood.
 		if (!rcu_segcblist_pend_cbs(&rdp->cblist)) {
@@ -544,7 +542,7 @@ static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
 		} else {
 			trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
 					    TPS("FirstBQnoWake"));
-			rcu_nocb_unlock_irqrestore(rdp, flags);
+			rcu_nocb_unlock(rdp);
 		}
 	}
 	return true; // Callback already enqueued.
@@ -566,11 +564,12 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
 	long lazy_len;
 	long len;
 	struct task_struct *t;
+	struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
 
 	// If we are being polled or there is no kthread, just leave.
 	t = READ_ONCE(rdp->nocb_gp_kthread);
 	if (rcu_nocb_poll || !t) {
-		rcu_nocb_unlock_irqrestore(rdp, flags);
+		rcu_nocb_unlock(rdp);
 		trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
 				    TPS("WakeNotPoll"));
 		return;
@@ -583,17 +582,17 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
 		rdp->qlen_last_fqs_check = len;
 		// Only lazy CBs in bypass list
 		if (lazy_len && bypass_len == lazy_len) {
-			rcu_nocb_unlock_irqrestore(rdp, flags);
+			rcu_nocb_unlock(rdp);
 			wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_LAZY,
 					   TPS("WakeLazy"));
 		} else if (!irqs_disabled_flags(flags)) {
 			/* ... if queue was empty ... */
-			rcu_nocb_unlock_irqrestore(rdp, flags);
+			rcu_nocb_unlock(rdp);
 			wake_nocb_gp(rdp, false);
 			trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
 					    TPS("WakeEmpty"));
 		} else {
-			rcu_nocb_unlock_irqrestore(rdp, flags);
+			rcu_nocb_unlock(rdp);
 			wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE,
 					   TPS("WakeEmptyIsDeferred"));
 		}
@@ -610,20 +609,32 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
 		smp_mb(); /* Enqueue before timer_pending(). */
 		if ((rdp->nocb_cb_sleep ||
 		     !rcu_segcblist_ready_cbs(&rdp->cblist)) &&
-		    !timer_pending(&rdp->nocb_timer)) {
-			rcu_nocb_unlock_irqrestore(rdp, flags);
+		    !timer_pending(&rdp_gp->nocb_timer)) {
+			rcu_nocb_unlock(rdp);
 			wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_FORCE,
 					   TPS("WakeOvfIsDeferred"));
 		} else {
-			rcu_nocb_unlock_irqrestore(rdp, flags);
+			rcu_nocb_unlock(rdp);
 			trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot"));
 		}
 	} else {
-		rcu_nocb_unlock_irqrestore(rdp, flags);
+		rcu_nocb_unlock(rdp);
 		trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot"));
 	}
 }
 
+static void call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *head,
+			  rcu_callback_t func, unsigned long flags, bool lazy)
+{
+	bool was_alldone;
+
+	if (!rcu_nocb_try_bypass(rdp, head, &was_alldone, flags, lazy)) {
+		/* Not enqueued on bypass but locked, do regular enqueue */
+		rcutree_enqueue(rdp, head, func);
+		__call_rcu_nocb_wake(rdp, was_alldone, flags); /* unlocks */
+	}
+}
+
 static int nocb_gp_toggle_rdp(struct rcu_data *rdp,
 			       bool *wake_state)
 {
@@ -723,7 +734,7 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
 		lazy_ncbs = READ_ONCE(rdp->lazy_len);
 
 		if (bypass_ncbs && (lazy_ncbs == bypass_ncbs) &&
-		    (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + jiffies_till_flush) ||
+		    (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + rcu_get_jiffies_lazy_flush()) ||
 		     bypass_ncbs > 2 * qhimark)) {
 			flush_bypass = true;
 		} else if (bypass_ncbs && (lazy_ncbs != bypass_ncbs) &&
@@ -779,7 +790,6 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
 		if (rcu_segcblist_ready_cbs(&rdp->cblist)) {
 			needwake = rdp->nocb_cb_sleep;
 			WRITE_ONCE(rdp->nocb_cb_sleep, false);
-			smp_mb(); /* CB invocation -after- GP end. */
 		} else {
 			needwake = false;
 		}
@@ -933,8 +943,7 @@ static void nocb_cb_wait(struct rcu_data *rdp)
 		swait_event_interruptible_exclusive(rdp->nocb_cb_wq,
 						    nocb_cb_wait_cond(rdp));
 
-		// VVV Ensure CB invocation follows _sleep test.
-		if (smp_load_acquire(&rdp->nocb_cb_sleep)) { // ^^^
+		if (READ_ONCE(rdp->nocb_cb_sleep)) {
 			WARN_ON(signal_pending(current));
 			trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WokeEmpty"));
 		}
@@ -1383,7 +1392,7 @@ lazy_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
 			rcu_nocb_unlock_irqrestore(rdp, flags);
 			continue;
 		}
-		WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies, false));
+		rcu_nocb_try_flush_bypass(rdp, jiffies);
 		rcu_nocb_unlock_irqrestore(rdp, flags);
 		wake_nocb_gp(rdp, false);
 		sc->nr_to_scan -= _count;
@@ -1768,10 +1777,10 @@ static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
 	return true;
 }
 
-static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
-				bool *was_alldone, unsigned long flags, bool lazy)
+static void call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *head,
+			  rcu_callback_t func, unsigned long flags, bool lazy)
 {
-	return false;
+	WARN_ON_ONCE(1);  /* Should be dead code! */
 }
 
 static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty,

kernel/rcu/tree_plugin.h

@@ -1195,14 +1195,13 @@ static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
 	struct sched_param sp;
 	struct task_struct *t;
 
-	mutex_lock(&rnp->boost_kthread_mutex);
-	if (rnp->boost_kthread_task || !rcu_scheduler_fully_active)
-		goto out;
+	if (rnp->boost_kthread_task)
+		return;
 
 	t = kthread_create(rcu_boost_kthread, (void *)rnp,
 			   "rcub/%d", rnp_index);
 	if (WARN_ON_ONCE(IS_ERR(t)))
-		goto out;
+		return;
 
 	raw_spin_lock_irqsave_rcu_node(rnp, flags);
 	rnp->boost_kthread_task = t;
@@ -1210,48 +1209,11 @@ static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
 	sp.sched_priority = kthread_prio;
 	sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
 	wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
-
- out:
-	mutex_unlock(&rnp->boost_kthread_mutex);
 }
 
-/*
- * Set the per-rcu_node kthread's affinity to cover all CPUs that are
- * served by the rcu_node in question.  The CPU hotplug lock is still
- * held, so the value of rnp->qsmaskinit will be stable.
- *
- * We don't include outgoingcpu in the affinity set, use -1 if there is
- * no outgoing CPU.  If there are no CPUs left in the affinity set,
- * this function allows the kthread to execute on any CPU.
- *
- * Any future concurrent calls are serialized via ->boost_kthread_mutex.
- */
-static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
+static struct task_struct *rcu_boost_task(struct rcu_node *rnp)
 {
-	struct task_struct *t = rnp->boost_kthread_task;
-	unsigned long mask;
-	cpumask_var_t cm;
-	int cpu;
-
-	if (!t)
-		return;
-	if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
-		return;
-	mutex_lock(&rnp->boost_kthread_mutex);
-	mask = rcu_rnp_online_cpus(rnp);
-	for_each_leaf_node_possible_cpu(rnp, cpu)
-		if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
-		    cpu != outgoingcpu)
-			cpumask_set_cpu(cpu, cm);
-	cpumask_and(cm, cm, housekeeping_cpumask(HK_TYPE_RCU));
-	if (cpumask_empty(cm)) {
-		cpumask_copy(cm, housekeeping_cpumask(HK_TYPE_RCU));
-		if (outgoingcpu >= 0)
-			cpumask_clear_cpu(outgoingcpu, cm);
-	}
-	set_cpus_allowed_ptr(t, cm);
-	mutex_unlock(&rnp->boost_kthread_mutex);
-	free_cpumask_var(cm);
+	return READ_ONCE(rnp->boost_kthread_task);
 }
 
 #else /* #ifdef CONFIG_RCU_BOOST */
@@ -1270,10 +1232,10 @@ static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
 {
 }
 
-static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
+static struct task_struct *rcu_boost_task(struct rcu_node *rnp)
 {
+	return NULL;
 }
-
 #endif /* #else #ifdef CONFIG_RCU_BOOST */
 
 /*