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

Pull RCU updates from Ingo Molnar:

 - updates to the handling of expedited grace periods

 - updates to reduce lock contention in the rcu_node combining tree

   [ These are in preparation for the consolidation of RCU-bh,
     RCU-preempt, and RCU-sched into a single flavor, which was
     requested by Linus in response to a security flaw whose root cause
     included confusion between the multiple flavors of RCU ]

 - torture-test updates that save their users some time and effort

 - miscellaneous fixes

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (44 commits)
  rcu/x86: Provide early rcu_cpu_starting() callback
  torture: Make kvm-find-errors.sh find build warnings
  rcutorture: Abbreviate kvm.sh summary lines
  rcutorture: Print end-of-test state in kvm.sh summary
  rcutorture: Print end-of-test state
  torture: Fold parse-torture.sh into parse-console.sh
  torture: Add a script to edit output from failed runs
  rcu: Update list of rcu_future_grace_period() trace events
  rcu: Drop early GP request check from rcu_gp_kthread()
  rcu: Simplify and inline cpu_needs_another_gp()
  rcu: The rcu_gp_cleanup() function does not need cpu_needs_another_gp()
  rcu: Make rcu_start_this_gp() check for out-of-range requests
  rcu: Add funnel locking to rcu_start_this_gp()
  rcu: Make rcu_start_future_gp() caller select grace period
  rcu: Inline rcu_start_gp_advanced() into rcu_start_future_gp()
  rcu: Clear request other than RCU_GP_FLAG_INIT at GP end
  rcu: Cleanup, don't put ->completed into an int
  rcu: Switch __rcu_process_callbacks() to rcu_accelerate_cbs()
  rcu: Avoid __call_rcu_core() root rcu_node ->lock acquisition
  rcu: Make rcu_migrate_callbacks wake GP kthread when needed
  ...

Documentation/RCU/whatisRCU.txt

+What is RCU?  --  "Read, Copy, Update"
+
 Please note that the "What is RCU?" LWN series is an excellent place
 to start learning about RCU:
 

arch/x86/kernel/cpu/mtrr/main.c

@@ -46,6 +46,7 @@
 #include <linux/pci.h>
 #include <linux/smp.h>
 #include <linux/syscore_ops.h>
+#include <linux/rcupdate.h>
 
 #include <asm/cpufeature.h>
 #include <asm/e820/api.h>
@@ -793,6 +794,9 @@ void mtrr_ap_init(void)
 
 	if (!use_intel() || mtrr_aps_delayed_init)
 		return;
+
+	rcu_cpu_starting(smp_processor_id());
+
 	/*
 	 * Ideally we should hold mtrr_mutex here to avoid mtrr entries
 	 * changed, but this routine will be called in cpu boot time,

drivers/nvme/host/core.c

@@ -357,7 +357,7 @@ static void nvme_free_ns_head(struct kref *ref)
 	nvme_mpath_remove_disk(head);
 	ida_simple_remove(&head->subsys->ns_ida, head->instance);
 	list_del_init(&head->entry);
-	cleanup_srcu_struct(&head->srcu);
+	cleanup_srcu_struct_quiesced(&head->srcu);
 	nvme_put_subsystem(head->subsys);
 	kfree(head);
 }

include/linux/rcupdate.h

@@ -108,7 +108,6 @@ void rcu_sched_qs(void);
 void rcu_bh_qs(void);
 void rcu_check_callbacks(int user);
 void rcu_report_dead(unsigned int cpu);
-void rcu_cpu_starting(unsigned int cpu);
 void rcutree_migrate_callbacks(int cpu);
 
 #ifdef CONFIG_RCU_STALL_COMMON
@@ -188,13 +187,13 @@ static inline void exit_tasks_rcu_finish(void) { }
 #endif /* #else #ifdef CONFIG_TASKS_RCU */
 
 /**
- * cond_resched_rcu_qs - Report potential quiescent states to RCU
+ * cond_resched_tasks_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() \
+#define cond_resched_tasks_rcu_qs() \
 do { \
 	if (!cond_resched()) \
 		rcu_note_voluntary_context_switch_lite(current); \

include/linux/rcutiny.h

@@ -132,5 +132,6 @@ static inline void rcu_all_qs(void) { barrier(); }
 #define rcutree_offline_cpu      NULL
 #define rcutree_dead_cpu         NULL
 #define rcutree_dying_cpu        NULL
+static inline void rcu_cpu_starting(unsigned int cpu) { }
 
 #endif /* __LINUX_RCUTINY_H */

include/linux/rcutree.h

@@ -74,6 +74,7 @@ static inline void synchronize_rcu_bh_expedited(void)
 void rcu_barrier(void);
 void rcu_barrier_bh(void);
 void rcu_barrier_sched(void);
+bool rcu_eqs_special_set(int cpu);
 unsigned long get_state_synchronize_rcu(void);
 void cond_synchronize_rcu(unsigned long oldstate);
 unsigned long get_state_synchronize_sched(void);
@@ -100,5 +101,6 @@ int rcutree_online_cpu(unsigned int cpu);
 int rcutree_offline_cpu(unsigned int cpu);
 int rcutree_dead_cpu(unsigned int cpu);
 int rcutree_dying_cpu(unsigned int cpu);
+void rcu_cpu_starting(unsigned int cpu);
 
 #endif /* __LINUX_RCUTREE_H */

include/linux/sched.h

@@ -1661,7 +1661,6 @@ static inline int test_tsk_need_resched(struct task_struct *tsk)
  * explicit rescheduling in places that are safe. The return
  * value indicates whether a reschedule was done in fact.
  * cond_resched_lock() will drop the spinlock before scheduling,
- * cond_resched_softirq() will enable bhs before scheduling.
  */
 #ifndef CONFIG_PREEMPT
 extern int _cond_resched(void);
@@ -1681,13 +1680,6 @@ extern int __cond_resched_lock(spinlock_t *lock);
 	__cond_resched_lock(lock);				\
 })
 
-extern int __cond_resched_softirq(void);
-
-#define cond_resched_softirq() ({					\
-	___might_sleep(__FILE__, __LINE__, SOFTIRQ_DISABLE_OFFSET);	\
-	__cond_resched_softirq();					\
-})
-
 static inline void cond_resched_rcu(void)
 {
 #if defined(CONFIG_DEBUG_ATOMIC_SLEEP) || !defined(CONFIG_PREEMPT_RCU)

include/linux/srcu.h

@@ -69,11 +69,45 @@ struct srcu_struct { };
 
 void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
 		void (*func)(struct rcu_head *head));
-void cleanup_srcu_struct(struct srcu_struct *sp);
+void _cleanup_srcu_struct(struct srcu_struct *sp, bool quiesced);
 int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
 void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
 void synchronize_srcu(struct srcu_struct *sp);
 
+/**
+ * cleanup_srcu_struct - deconstruct a sleep-RCU structure
+ * @sp: structure to clean up.
+ *
+ * Must invoke this after you are finished using a given srcu_struct that
+ * was initialized via init_srcu_struct(), else you leak memory.
+ */
+static inline void cleanup_srcu_struct(struct srcu_struct *sp)
+{
+	_cleanup_srcu_struct(sp, false);
+}
+
+/**
+ * cleanup_srcu_struct_quiesced - deconstruct a quiesced sleep-RCU structure
+ * @sp: structure to clean up.
+ *
+ * Must invoke this after you are finished using a given srcu_struct that
+ * was initialized via init_srcu_struct(), else you leak memory.  Also,
+ * all grace-period processing must have completed.
+ *
+ * "Completed" means that the last synchronize_srcu() and
+ * synchronize_srcu_expedited() calls must have returned before the call
+ * to cleanup_srcu_struct_quiesced().  It also means that the callback
+ * from the last call_srcu() must have been invoked before the call to
+ * cleanup_srcu_struct_quiesced(), but you can use srcu_barrier() to help
+ * with this last.  Violating these rules will get you a WARN_ON() splat
+ * (with high probability, anyway), and will also cause the srcu_struct
+ * to be leaked.
+ */
+static inline void cleanup_srcu_struct_quiesced(struct srcu_struct *sp)
+{
+	_cleanup_srcu_struct(sp, true);
+}
+
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 
 /**

include/trace/events/rcu.h

@@ -84,20 +84,21 @@ TRACE_EVENT(rcu_grace_period,
 );
 
 /*
- * Tracepoint for future grace-period events, including those for no-callbacks
- * CPUs.  The caller should pull the data from the rcu_node structure,
- * other than rcuname, which comes from the rcu_state structure, and event,
- * which is one of the following:
+ * Tracepoint for future grace-period events.  The caller should pull
+ * the data from the rcu_node structure, other than rcuname, which comes
+ * from the rcu_state structure, and event, which is one of the following:
  *
- * "Startleaf": Request a nocb grace period based on leaf-node data.
+ * "Startleaf": Request a grace period based on leaf-node data.
+ * "Prestarted": Someone beat us to the request
  * "Startedleaf": Leaf-node start proved sufficient.
  * "Startedleafroot": Leaf-node start proved sufficient after checking root.
  * "Startedroot": Requested a nocb grace period based on root-node data.
+ * "NoGPkthread": The RCU grace-period kthread has not yet started.
  * "StartWait": Start waiting for the requested grace period.
  * "ResumeWait": Resume waiting after signal.
  * "EndWait": Complete wait.
  * "Cleanup": Clean up rcu_node structure after previous GP.
- * "CleanupMore": Clean up, and another no-CB GP is needed.
+ * "CleanupMore": Clean up, and another GP is needed.
  */
 TRACE_EVENT(rcu_future_grace_period,
 

kernel/rcu/rcu.h

@@ -270,6 +270,12 @@ static inline void rcu_init_levelspread(int *levelspread, const int *levelcnt)
 	}
 }
 
+/* Returns first leaf rcu_node of the specified RCU flavor. */
+#define rcu_first_leaf_node(rsp) ((rsp)->level[rcu_num_lvls - 1])
+
+/* Is this rcu_node a leaf? */
+#define rcu_is_leaf_node(rnp) ((rnp)->level == rcu_num_lvls - 1)
+
 /*
  * Do a full breadth-first scan of the rcu_node structures for the
  * specified rcu_state structure.
@@ -284,8 +290,7 @@ static inline void rcu_init_levelspread(int *levelspread, const int *levelcnt)
  * rcu_node tree with but one rcu_node structure, this loop is a no-op.
  */
 #define rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) \
-	for ((rnp) = &(rsp)->node[0]; \
-	     (rnp) < (rsp)->level[rcu_num_lvls - 1]; (rnp)++)
+	for ((rnp) = &(rsp)->node[0]; !rcu_is_leaf_node(rsp, rnp); (rnp)++)
 
 /*
  * Scan the leaves of the rcu_node hierarchy for the specified rcu_state
@@ -294,7 +299,7 @@ static inline void rcu_init_levelspread(int *levelspread, const int *levelcnt)
  * It is still a leaf node, even if it is also the root node.
  */
 #define rcu_for_each_leaf_node(rsp, rnp) \
-	for ((rnp) = (rsp)->level[rcu_num_lvls - 1]; \
+	for ((rnp) = rcu_first_leaf_node(rsp); \
 	     (rnp) < &(rsp)->node[rcu_num_nodes]; (rnp)++)
 
 /*
@@ -486,6 +491,7 @@ void rcu_force_quiescent_state(void);
 void rcu_bh_force_quiescent_state(void);
 void rcu_sched_force_quiescent_state(void);
 extern struct workqueue_struct *rcu_gp_wq;
+extern struct workqueue_struct *rcu_par_gp_wq;
 #endif /* #else #ifdef CONFIG_TINY_RCU */
 
 #ifdef CONFIG_RCU_NOCB_CPU

kernel/rcu/rcu_segcblist.c

@@ -403,24 +403,6 @@ bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp, unsigned long seq)
 	return true;
 }
 
-/*
- * Scan the specified rcu_segcblist structure for callbacks that need
- * a grace period later than the one specified by "seq".  We don't look
- * at the RCU_DONE_TAIL or RCU_NEXT_TAIL segments because they don't
- * have a grace-period sequence number.
- */
-bool rcu_segcblist_future_gp_needed(struct rcu_segcblist *rsclp,
-				    unsigned long seq)
-{
-	int i;
-
-	for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++)
-		if (rsclp->tails[i - 1] != rsclp->tails[i] &&
-		    ULONG_CMP_LT(seq, rsclp->gp_seq[i]))
-			return true;
-	return false;
-}
-
 /*
  * Merge the source rcu_segcblist structure into the destination
  * rcu_segcblist structure, then initialize the source.  Any pending

kernel/rcu/rcu_segcblist.h

@@ -134,7 +134,5 @@ void rcu_segcblist_insert_pend_cbs(struct rcu_segcblist *rsclp,
 				   struct rcu_cblist *rclp);
 void rcu_segcblist_advance(struct rcu_segcblist *rsclp, unsigned long seq);
 bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp, unsigned long seq);
-bool rcu_segcblist_future_gp_needed(struct rcu_segcblist *rsclp,
-				    unsigned long seq);
 void rcu_segcblist_merge(struct rcu_segcblist *dst_rsclp,
 			 struct rcu_segcblist *src_rsclp);

kernel/rcu/rcuperf.c

@@ -369,7 +369,7 @@ static bool __maybe_unused torturing_tasks(void)
  */
 static void rcu_perf_wait_shutdown(void)
 {
-	cond_resched_rcu_qs();
+	cond_resched_tasks_rcu_qs();
 	if (atomic_read(&n_rcu_perf_writer_finished) < nrealwriters)
 		return;
 	while (!torture_must_stop())

kernel/rcu/rcutorture.c

@@ -593,7 +593,12 @@ static void srcu_torture_init(void)
 
 static void srcu_torture_cleanup(void)
 {
+	static DEFINE_TORTURE_RANDOM(rand);
+
+	if (torture_random(&rand) & 0x800)
 		cleanup_srcu_struct(&srcu_ctld);
+	else
+		cleanup_srcu_struct_quiesced(&srcu_ctld);
 	srcu_ctlp = &srcu_ctl; /* In case of a later rcutorture run. */
 }
 
@@ -1609,6 +1614,9 @@ static enum cpuhp_state rcutor_hp;
 static void
 rcu_torture_cleanup(void)
 {
+	int flags = 0;
+	unsigned long gpnum = 0;
+	unsigned long completed = 0;
 	int i;
 
 	rcutorture_record_test_transition();
@@ -1639,6 +1647,11 @@ rcu_torture_cleanup(void)
 		fakewriter_tasks = NULL;
 	}
 
+	rcutorture_get_gp_data(cur_ops->ttype, &flags, &gpnum, &completed);
+	srcutorture_get_gp_data(cur_ops->ttype, srcu_ctlp,
+				&flags, &gpnum, &completed);
+	pr_alert("%s:  End-test grace-period state: g%lu c%lu f%#x\n",
+		 cur_ops->name, gpnum, completed, flags);
 	torture_stop_kthread(rcu_torture_stats, stats_task);
 	torture_stop_kthread(rcu_torture_fqs, fqs_task);
 	for (i = 0; i < ncbflooders; i++)

kernel/rcu/srcutiny.c

@@ -86,16 +86,19 @@ EXPORT_SYMBOL_GPL(init_srcu_struct);
  * Must invoke this after you are finished using a given srcu_struct that
  * was initialized via init_srcu_struct(), else you leak memory.
  */
-void cleanup_srcu_struct(struct srcu_struct *sp)
+void _cleanup_srcu_struct(struct srcu_struct *sp, bool quiesced)
 {
 	WARN_ON(sp->srcu_lock_nesting[0] || sp->srcu_lock_nesting[1]);
+	if (quiesced)
+		WARN_ON(work_pending(&sp->srcu_work));
+	else
 		flush_work(&sp->srcu_work);
 	WARN_ON(sp->srcu_gp_running);
 	WARN_ON(sp->srcu_gp_waiting);
 	WARN_ON(sp->srcu_cb_head);
 	WARN_ON(&sp->srcu_cb_head != sp->srcu_cb_tail);
 }
-EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
+EXPORT_SYMBOL_GPL(_cleanup_srcu_struct);
 
 /*
  * Removes the count for the old reader from the appropriate element of

kernel/rcu/srcutree.c

@@ -366,24 +366,28 @@ static unsigned long srcu_get_delay(struct srcu_struct *sp)
 	return SRCU_INTERVAL;
 }
 
-/**
- * cleanup_srcu_struct - deconstruct a sleep-RCU structure
- * @sp: structure to clean up.
- *
- * Must invoke this after you are finished using a given srcu_struct that
- * was initialized via init_srcu_struct(), else you leak memory.
- */
-void cleanup_srcu_struct(struct srcu_struct *sp)
+/* Helper for cleanup_srcu_struct() and cleanup_srcu_struct_quiesced(). */
+void _cleanup_srcu_struct(struct srcu_struct *sp, bool quiesced)
 {
 	int cpu;
 
 	if (WARN_ON(!srcu_get_delay(sp)))
-		return; /* Leakage unless caller handles error. */
+		return; /* Just leak it! */
 	if (WARN_ON(srcu_readers_active(sp)))
-		return; /* Leakage unless caller handles error. */
+		return; /* Just leak it! */
+	if (quiesced) {
+		if (WARN_ON(delayed_work_pending(&sp->work)))
+			return; /* Just leak it! */
+	} else {
 		flush_delayed_work(&sp->work);
+	}
 	for_each_possible_cpu(cpu)
+		if (quiesced) {
+			if (WARN_ON(delayed_work_pending(&per_cpu_ptr(sp->sda, cpu)->work)))
+				return; /* Just leak it! */
+		} else {
 			flush_delayed_work(&per_cpu_ptr(sp->sda, cpu)->work);
+		}
 	if (WARN_ON(rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) != SRCU_STATE_IDLE) ||
 	    WARN_ON(srcu_readers_active(sp))) {
 		pr_info("%s: Active srcu_struct %p state: %d\n", __func__, sp, rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)));
@@ -392,7 +396,7 @@ void cleanup_srcu_struct(struct srcu_struct *sp)
 	free_percpu(sp->sda);
 	sp->sda = NULL;
 }
-EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
+EXPORT_SYMBOL_GPL(_cleanup_srcu_struct);
 
 /*
  * Counts the new reader in the appropriate per-CPU element of the

kernel/rcu/tree.c

@@ -524,8 +524,6 @@ module_param(rcu_kick_kthreads, bool, 0644);
 static ulong jiffies_till_sched_qs = HZ / 10;
 module_param(jiffies_till_sched_qs, ulong, 0444);
 
-static bool rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
-				  struct rcu_data *rdp);
 static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *rsp));
 static void force_quiescent_state(struct rcu_state *rsp);
 static int rcu_pending(void);
@@ -710,44 +708,6 @@ static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
 	return &rsp->node[0];
 }
 
-/*
- * Is there any need for future grace periods?
- * Interrupts must be disabled.  If the caller does not hold the root
- * rnp_node structure's ->lock, the results are advisory only.
- */
-static int rcu_future_needs_gp(struct rcu_state *rsp)
-{
-	struct rcu_node *rnp = rcu_get_root(rsp);
-	int idx = (READ_ONCE(rnp->completed) + 1) & 0x1;
-	int *fp = &rnp->need_future_gp[idx];
-
-	lockdep_assert_irqs_disabled();
-	return READ_ONCE(*fp);
-}
-
-/*
- * Does the current CPU require a not-yet-started grace period?
- * The caller must have disabled interrupts to prevent races with
- * normal callback registry.
- */
-static bool
-cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
-{
-	lockdep_assert_irqs_disabled();
-	if (rcu_gp_in_progress(rsp))
-		return false;  /* No, a grace period is already in progress. */
-	if (rcu_future_needs_gp(rsp))
-		return true;  /* Yes, a no-CBs CPU needs one. */
-	if (!rcu_segcblist_is_enabled(&rdp->cblist))
-		return false;  /* No, this is a no-CBs (or offline) CPU. */
-	if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
-		return true;  /* Yes, CPU has newly registered callbacks. */
-	if (rcu_segcblist_future_gp_needed(&rdp->cblist,
-					   READ_ONCE(rsp->completed)))
-		return true;  /* Yes, CBs for future grace period. */
-	return false; /* No grace period needed. */
-}
-
 /*
  * Enter an RCU extended quiescent state, which can be either the
  * idle loop or adaptive-tickless usermode execution.
@@ -1234,10 +1194,10 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
 	}
 
 	/*
-	 * Has this CPU encountered a cond_resched_rcu_qs() since the
-	 * beginning of the grace period?  For this to be the case,
-	 * the CPU has to have noticed the current grace period.  This
-	 * might not be the case for nohz_full CPUs looping in the kernel.
+	 * Has this CPU encountered a cond_resched() since the beginning
+	 * of the grace period?  For this to be the case, the CPU has to
+	 * have noticed the current grace period.  This might not be the
+	 * case for nohz_full CPUs looping in the kernel.
 	 */
 	jtsq = jiffies_till_sched_qs;
 	ruqp = per_cpu_ptr(&rcu_dynticks.rcu_urgent_qs, rdp->cpu);
@@ -1641,6 +1601,21 @@ static unsigned long rcu_cbs_completed(struct rcu_state *rsp,
 	if (rcu_get_root(rsp) == rnp && rnp->gpnum == rnp->completed)
 		return rnp->completed + 1;
 
+	/*
+	 * If the current rcu_node structure believes that RCU is
+	 * idle, and if the rcu_state structure does not yet reflect
+	 * the start of a new grace period, then the next grace period
+	 * will suffice.  The memory barrier is needed to accurately
+	 * sample the rsp->gpnum, and pairs with the second lock
+	 * acquisition in rcu_gp_init(), which is augmented with
+	 * smp_mb__after_unlock_lock() for this purpose.
+	 */
+	if (rnp->gpnum == rnp->completed) {
+		smp_mb(); /* See above block comment. */
+		if (READ_ONCE(rsp->gpnum) == rnp->completed)
+			return rnp->completed + 1;
+	}
+
 	/*
 	 * Otherwise, wait for a possible partial grace period and
 	 * then the subsequent full grace period.
@@ -1648,11 +1623,8 @@ static unsigned long rcu_cbs_completed(struct rcu_state *rsp,
 	return rnp->completed + 2;
 }
 
-/*
- * Trace-event helper function for rcu_start_future_gp() and
- * rcu_nocb_wait_gp().
- */
-static void trace_rcu_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
+/* Trace-event wrapper function for trace_rcu_future_grace_period.  */
+static void trace_rcu_this_gp(struct rcu_node *rnp, struct rcu_data *rdp,
 			      unsigned long c, const char *s)
 {
 	trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum,
@@ -1661,96 +1633,67 @@ static void trace_rcu_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
 }
 
 /*
- * Start some future grace period, as needed to handle newly arrived
+ * Start the specified grace period, as needed to handle newly arrived
  * callbacks.  The required future grace periods are recorded in each
- * rcu_node structure's ->need_future_gp field.  Returns true if there
+ * rcu_node structure's ->need_future_gp[] field.  Returns true if there
  * is reason to awaken the grace-period kthread.
  *
- * The caller must hold the specified rcu_node structure's ->lock.
+ * The caller must hold the specified rcu_node structure's ->lock, which
+ * is why the caller is responsible for waking the grace-period kthread.
  */
-static bool __maybe_unused
-rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
-		    unsigned long *c_out)
+static bool rcu_start_this_gp(struct rcu_node *rnp, struct rcu_data *rdp,
+			      unsigned long c)
 {
-	unsigned long c;
 	bool ret = false;
-	struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);
-
-	raw_lockdep_assert_held_rcu_node(rnp);
-
-	/*
-	 * Pick up grace-period number for new callbacks.  If this
-	 * grace period is already marked as needed, return to the caller.
-	 */
-	c = rcu_cbs_completed(rdp->rsp, rnp);
-	trace_rcu_future_gp(rnp, rdp, c, TPS("Startleaf"));
-	if (rnp->need_future_gp[c & 0x1]) {
-		trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartleaf"));
-		goto out;
-	}
-
-	/*
-	 * If either this rcu_node structure or the root rcu_node structure
-	 * believe that a grace period is in progress, then we must wait
-	 * for the one following, which is in "c".  Because our request
-	 * will be noticed at the end of the current grace period, we don't
-	 * need to explicitly start one.  We only do the lockless check
-	 * of rnp_root's fields if the current rcu_node structure thinks
-	 * there is no grace period in flight, and because we hold rnp->lock,
-	 * the only possible change is when rnp_root's two fields are
-	 * equal, in which case rnp_root->gpnum might be concurrently
-	 * incremented.  But that is OK, as it will just result in our
-	 * doing some extra useless work.
-	 */
-	if (rnp->gpnum != rnp->completed ||
-	    READ_ONCE(rnp_root->gpnum) != READ_ONCE(rnp_root->completed)) {
-		rnp->need_future_gp[c & 0x1]++;
-		trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleaf"));
-		goto out;
-	}
+	struct rcu_state *rsp = rdp->rsp;
+	struct rcu_node *rnp_root;
 
 	/*
-	 * There might be no grace period in progress.  If we don't already
-	 * hold it, acquire the root rcu_node structure's lock in order to
-	 * start one (if needed).
+	 * Use funnel locking to either acquire the root rcu_node
+	 * structure's lock or bail out if the need for this grace period
+	 * has already been recorded -- or has already started.  If there
+	 * is already a grace period in progress in a non-leaf node, no
+	 * recording is needed because the end of the grace period will
+	 * scan the leaf rcu_node structures.  Note that rnp->lock must
+	 * not be released.
 	 */
-	if (rnp != rnp_root)
+	raw_lockdep_assert_held_rcu_node(rnp);
+	trace_rcu_this_gp(rnp, rdp, c, TPS("Startleaf"));
+	for (rnp_root = rnp; 1; rnp_root = rnp_root->parent) {
+		if (rnp_root != rnp)
 			raw_spin_lock_rcu_node(rnp_root);
-
-	/*
-	 * Get a new grace-period number.  If there really is no grace
-	 * period in progress, it will be smaller than the one we obtained
-	 * earlier.  Adjust callbacks as needed.
-	 */
-	c = rcu_cbs_completed(rdp->rsp, rnp_root);
-	if (!rcu_is_nocb_cpu(rdp->cpu))
-		(void)rcu_segcblist_accelerate(&rdp->cblist, c);
-
-	/*
-	 * If the needed for the required grace period is already
-	 * recorded, trace and leave.
-	 */
-	if (rnp_root->need_future_gp[c & 0x1]) {
-		trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartedroot"));
+		WARN_ON_ONCE(ULONG_CMP_LT(rnp_root->gpnum +
+					  need_future_gp_mask(), c));
+		if (need_future_gp_element(rnp_root, c) ||
+		    ULONG_CMP_GE(rnp_root->gpnum, c) ||
+		    (rnp != rnp_root &&
+		     rnp_root->gpnum != rnp_root->completed)) {
+			trace_rcu_this_gp(rnp_root, rdp, c, TPS("Prestarted"));
 			goto unlock_out;
 		}
+		need_future_gp_element(rnp_root, c) = true;
+		if (rnp_root != rnp && rnp_root->parent != NULL)
+			raw_spin_unlock_rcu_node(rnp_root);
+		if (!rnp_root->parent)
+			break;  /* At root, and perhaps also leaf. */
+	}
 
-	/* Record the need for the future grace period. */
-	rnp_root->need_future_gp[c & 0x1]++;
-
-	/* If a grace period is not already in progress, start one. */
+	/* If GP already in progress, just leave, otherwise start one. */
 	if (rnp_root->gpnum != rnp_root->completed) {
-		trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleafroot"));
-	} else {
-		trace_rcu_future_gp(rnp, rdp, c, TPS("Startedroot"));
-		ret = rcu_start_gp_advanced(rdp->rsp, rnp_root, rdp);
+		trace_rcu_this_gp(rnp_root, rdp, c, TPS("Startedleafroot"));
+		goto unlock_out;
+	}
+	trace_rcu_this_gp(rnp_root, rdp, c, TPS("Startedroot"));
+	WRITE_ONCE(rsp->gp_flags, rsp->gp_flags | RCU_GP_FLAG_INIT);
+	if (!rsp->gp_kthread) {
+		trace_rcu_this_gp(rnp_root, rdp, c, TPS("NoGPkthread"));
+		goto unlock_out;
 	}
+	trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gpnum), TPS("newreq"));
+	ret = true;  /* Caller must wake GP kthread. */
 unlock_out:
 	if (rnp != rnp_root)
 		raw_spin_unlock_rcu_node(rnp_root);
-out:
-	if (c_out != NULL)
-		*c_out = c;
 	return ret;
 }
 
@@ -1758,15 +1701,15 @@ rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
  * Clean up any old requests for the just-ended grace period.  Also return
  * whether any additional grace periods have been requested.
  */
-static int rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
+static bool rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
 {
-	int c = rnp->completed;
-	int needmore;
+	unsigned long c = rnp->completed;
+	bool needmore;
 	struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
 
-	rnp->need_future_gp[c & 0x1] = 0;
-	needmore = rnp->need_future_gp[(c + 1) & 0x1];
-	trace_rcu_future_gp(rnp, rdp, c,
+	need_future_gp_element(rnp, c) = false;
+	needmore = need_any_future_gp(rnp);
+	trace_rcu_this_gp(rnp, rdp, c,
 			  needmore ? TPS("CleanupMore") : TPS("Cleanup"));
 	return needmore;
 }
@@ -1802,6 +1745,7 @@ static void rcu_gp_kthread_wake(struct rcu_state *rsp)
 static bool rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
 			       struct rcu_data *rdp)
 {
+	unsigned long c;
 	bool ret = false;
 
 	raw_lockdep_assert_held_rcu_node(rnp);
@@ -1820,8 +1764,9 @@ static bool rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
 	 * accelerating callback invocation to an earlier grace-period
 	 * number.
 	 */
-	if (rcu_segcblist_accelerate(&rdp->cblist, rcu_cbs_completed(rsp, rnp)))
-		ret = rcu_start_future_gp(rnp, rdp, NULL);
+	c = rcu_cbs_completed(rsp, rnp);
+	if (rcu_segcblist_accelerate(&rdp->cblist, c))
+		ret = rcu_start_this_gp(rnp, rdp, c);
 
 	/* Trace depending on how much we were able to accelerate. */
 	if (rcu_segcblist_restempty(&rdp->cblist, RCU_WAIT_TAIL))
@@ -2049,7 +1994,7 @@ static bool rcu_gp_init(struct rcu_state *rsp)
 					    rnp->level, rnp->grplo,
 					    rnp->grphi, rnp->qsmask);
 		raw_spin_unlock_irq_rcu_node(rnp);
-		cond_resched_rcu_qs();
+		cond_resched_tasks_rcu_qs();
 		WRITE_ONCE(rsp->gp_activity, jiffies);
 	}
 
@@ -2108,7 +2053,6 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
 {
 	unsigned long gp_duration;
 	bool needgp = false;
-	int nocb = 0;
 	struct rcu_data *rdp;
 	struct rcu_node *rnp = rcu_get_root(rsp);
 	struct swait_queue_head *sq;
@@ -2147,31 +2091,35 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
 		if (rnp == rdp->mynode)
 			needgp = __note_gp_changes(rsp, rnp, rdp) || needgp;
 		/* smp_mb() provided by prior unlock-lock pair. */
-		nocb += rcu_future_gp_cleanup(rsp, rnp);
+		needgp = rcu_future_gp_cleanup(rsp, rnp) || needgp;
 		sq = rcu_nocb_gp_get(rnp);
 		raw_spin_unlock_irq_rcu_node(rnp);
 		rcu_nocb_gp_cleanup(sq);
-		cond_resched_rcu_qs();
+		cond_resched_tasks_rcu_qs();
 		WRITE_ONCE(rsp->gp_activity, jiffies);
 		rcu_gp_slow(rsp, gp_cleanup_delay);
 	}
 	rnp = rcu_get_root(rsp);
 	raw_spin_lock_irq_rcu_node(rnp); /* Order GP before ->completed update. */
-	rcu_nocb_gp_set(rnp, nocb);
 
 	/* Declare grace period done. */
 	WRITE_ONCE(rsp->completed, rsp->gpnum);
 	trace_rcu_grace_period(rsp->name, rsp->completed, TPS("end"));
 	rsp->gp_state = RCU_GP_IDLE;
+	/* Check for GP requests since above loop. */
 	rdp = this_cpu_ptr(rsp->rda);
+	if (need_any_future_gp(rnp)) {
+		trace_rcu_this_gp(rnp, rdp, rsp->completed - 1,
+				  TPS("CleanupMore"));
+		needgp = true;
+	}
 	/* Advance CBs to reduce false positives below. */
-	needgp = rcu_advance_cbs(rsp, rnp, rdp) || needgp;
-	if (needgp || cpu_needs_another_gp(rsp, rdp)) {
+	if (!rcu_accelerate_cbs(rsp, rnp, rdp) && needgp) {
 		WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT);
-		trace_rcu_grace_period(rsp->name,
-				       READ_ONCE(rsp->gpnum),
+		trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gpnum),
 				       TPS("newreq"));
 	}
+	WRITE_ONCE(rsp->gp_flags, rsp->gp_flags & RCU_GP_FLAG_INIT);
 	raw_spin_unlock_irq_rcu_node(rnp);
 }
 
@@ -2202,7 +2150,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
 			/* Locking provides needed memory barrier. */
 			if (rcu_gp_init(rsp))
 				break;
-			cond_resched_rcu_qs();
+			cond_resched_tasks_rcu_qs();
 			WRITE_ONCE(rsp->gp_activity, jiffies);
 			WARN_ON(signal_pending(current));
 			trace_rcu_grace_period(rsp->name,
@@ -2247,7 +2195,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
 				trace_rcu_grace_period(rsp->name,
 						       READ_ONCE(rsp->gpnum),
 						       TPS("fqsend"));
-				cond_resched_rcu_qs();
+				cond_resched_tasks_rcu_qs();
 				WRITE_ONCE(rsp->gp_activity, jiffies);
 				ret = 0; /* Force full wait till next FQS. */
 				j = jiffies_till_next_fqs;
@@ -2260,7 +2208,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
 				}
 			} else {
 				/* Deal with stray signal. */
-				cond_resched_rcu_qs();
+				cond_resched_tasks_rcu_qs();
 				WRITE_ONCE(rsp->gp_activity, jiffies);
 				WARN_ON(signal_pending(current));
 				trace_rcu_grace_period(rsp->name,
@@ -2282,71 +2230,6 @@ static int __noreturn rcu_gp_kthread(void *arg)
 	}
 }
 
-/*
- * Start a new RCU grace period if warranted, re-initializing the hierarchy
- * in preparation for detecting the next grace period.  The caller must hold
- * the root node's ->lock and hard irqs must be disabled.
- *
- * Note that it is legal for a dying CPU (which is marked as offline) to
- * invoke this function.  This can happen when the dying CPU reports its
- * quiescent state.
- *
- * Returns true if the grace-period kthread must be awakened.
- */
-static bool
-rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
-		      struct rcu_data *rdp)
-{
-	raw_lockdep_assert_held_rcu_node(rnp);
-	if (!rsp->gp_kthread || !cpu_needs_another_gp(rsp, rdp)) {
-		/*
-		 * Either we have not yet spawned the grace-period
-		 * task, this CPU does not need another grace period,
-		 * or a grace period is already in progress.
-		 * Either way, don't start a new grace period.
-		 */
-		return false;
-	}
-	WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT);
-	trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gpnum),
-			       TPS("newreq"));
-
-	/*
-	 * We can't do wakeups while holding the rnp->lock, as that
-	 * could cause possible deadlocks with the rq->lock. Defer
-	 * the wakeup to our caller.
-	 */
-	return true;
-}
-
-/*
- * Similar to rcu_start_gp_advanced(), but also advance the calling CPU's
- * callbacks.  Note that rcu_start_gp_advanced() cannot do this because it
- * is invoked indirectly from rcu_advance_cbs(), which would result in
- * endless recursion -- or would do so if it wasn't for the self-deadlock
- * that is encountered beforehand.
- *
- * Returns true if the grace-period kthread needs to be awakened.
- */
-static bool rcu_start_gp(struct rcu_state *rsp)
-{
-	struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
-	struct rcu_node *rnp = rcu_get_root(rsp);
-	bool ret = false;
-
-	/*
-	 * If there is no grace period in progress right now, any
-	 * callbacks we have up to this point will be satisfied by the
-	 * next grace period.  Also, advancing the callbacks reduces the
-	 * probability of false positives from cpu_needs_another_gp()
-	 * resulting in pointless grace periods.  So, advance callbacks
-	 * then start the grace period!
-	 */
-	ret = rcu_advance_cbs(rsp, rnp, rdp) || ret;
-	ret = rcu_start_gp_advanced(rsp, rnp, rdp) || ret;
-	return ret;
-}
-
 /*
  * Report a full set of quiescent states to the specified rcu_state data
  * structure.  Invoke rcu_gp_kthread_wake() to awaken the grace-period
@@ -2398,7 +2281,7 @@ rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
 			return;
 		}
 		WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */
-		WARN_ON_ONCE(rnp->level != rcu_num_lvls - 1 &&
+		WARN_ON_ONCE(!rcu_is_leaf_node(rnp) &&
 			     rcu_preempt_blocked_readers_cgp(rnp));
 		rnp->qsmask &= ~mask;
 		trace_rcu_quiescent_state_report(rsp->name, rnp->gpnum,
@@ -2782,7 +2665,7 @@ static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *rsp))
 	struct rcu_node *rnp;
 
 	rcu_for_each_leaf_node(rsp, rnp) {
-		cond_resched_rcu_qs();
+		cond_resched_tasks_rcu_qs();
 		mask = 0;
 		raw_spin_lock_irqsave_rcu_node(rnp, flags);
 		if (rnp->qsmask == 0) {
@@ -2874,22 +2757,27 @@ __rcu_process_callbacks(struct rcu_state *rsp)
 	unsigned long flags;
 	bool needwake;
 	struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
+	struct rcu_node *rnp;
 
 	WARN_ON_ONCE(!rdp->beenonline);
 
 	/* Update RCU state based on any recent quiescent states. */
 	rcu_check_quiescent_state(rsp, rdp);
 
-	/* Does this CPU require a not-yet-started grace period? */
+	/* No grace period and unregistered callbacks? */
+	if (!rcu_gp_in_progress(rsp) &&
+	    rcu_segcblist_is_enabled(&rdp->cblist)) {
 		local_irq_save(flags);
-	if (cpu_needs_another_gp(rsp, rdp)) {
-		raw_spin_lock_rcu_node(rcu_get_root(rsp)); /* irqs disabled. */
-		needwake = rcu_start_gp(rsp);
-		raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(rsp), flags);
+		if (rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL)) {
+			local_irq_restore(flags);
+		} else {
+			rnp = rdp->mynode;
+			raw_spin_lock_rcu_node(rnp); /* irqs disabled. */
+			needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
+			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 			if (needwake)
 				rcu_gp_kthread_wake(rsp);
-	} else {
-		local_irq_restore(flags);
+		}
 	}
 
 	/* If there are callbacks ready, invoke them. */
@@ -2973,11 +2861,11 @@ static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
 
 		/* Start a new grace period if one not already started. */
 		if (!rcu_gp_in_progress(rsp)) {
-			struct rcu_node *rnp_root = rcu_get_root(rsp);
+			struct rcu_node *rnp = rdp->mynode;
 
-			raw_spin_lock_rcu_node(rnp_root);
-			needwake = rcu_start_gp(rsp);
-			raw_spin_unlock_rcu_node(rnp_root);
+			raw_spin_lock_rcu_node(rnp);
+			needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
+			raw_spin_unlock_rcu_node(rnp);
 			if (needwake)
 				rcu_gp_kthread_wake(rsp);
 		} else {
@@ -3368,7 +3256,9 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
 		return 1;
 
 	/* Has RCU gone idle with this CPU needing another grace period? */
-	if (cpu_needs_another_gp(rsp, rdp))
+	if (!rcu_gp_in_progress(rsp) &&
+	    rcu_segcblist_is_enabled(&rdp->cblist) &&
+	    !rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
 		return 1;
 
 	/* Has another RCU grace period completed?  */
@@ -3775,6 +3665,8 @@ int rcutree_dead_cpu(unsigned int cpu)
 	return 0;
 }
 
+static DEFINE_PER_CPU(int, rcu_cpu_started);
+
 /*
  * Mark the specified CPU as being online so that subsequent grace periods
  * (both expedited and normal) will wait on it.  Note that this means that
@@ -3796,6 +3688,11 @@ void rcu_cpu_starting(unsigned int cpu)
 	struct rcu_node *rnp;
 	struct rcu_state *rsp;
 
+	if (per_cpu(rcu_cpu_started, cpu))
+		return;
+
+	per_cpu(rcu_cpu_started, cpu) = 1;
+
 	for_each_rcu_flavor(rsp) {
 		rdp = per_cpu_ptr(rsp->rda, cpu);
 		rnp = rdp->mynode;
@@ -3852,6 +3749,8 @@ void rcu_report_dead(unsigned int cpu)
 	preempt_enable();
 	for_each_rcu_flavor(rsp)
 		rcu_cleanup_dying_idle_cpu(cpu, rsp);
+
+	per_cpu(rcu_cpu_started, cpu) = 0;
 }
 
 /* Migrate the dead CPU's callbacks to the current CPU. */
@@ -3861,6 +3760,7 @@ static void rcu_migrate_callbacks(int cpu, struct rcu_state *rsp)
 	struct rcu_data *my_rdp;
 	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
 	struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);
+	bool needwake;
 
 	if (rcu_is_nocb_cpu(cpu) || rcu_segcblist_empty(&rdp->cblist))
 		return;  /* No callbacks to migrate. */
@@ -3872,12 +3772,15 @@ static void rcu_migrate_callbacks(int cpu, struct rcu_state *rsp)
 		return;
 	}
 	raw_spin_lock_rcu_node(rnp_root); /* irqs already disabled. */
-	rcu_advance_cbs(rsp, rnp_root, rdp); /* Leverage recent GPs. */
-	rcu_advance_cbs(rsp, rnp_root, my_rdp); /* Assign GP to pending CBs. */
+	/* Leverage recent GPs and set GP for new callbacks. */
+	needwake = rcu_advance_cbs(rsp, rnp_root, rdp) ||
+		   rcu_advance_cbs(rsp, rnp_root, my_rdp);
 	rcu_segcblist_merge(&my_rdp->cblist, &rdp->cblist);
 	WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) !=
 		     !rcu_segcblist_n_cbs(&my_rdp->cblist));
 	raw_spin_unlock_irqrestore_rcu_node(rnp_root, flags);
+	if (needwake)
+		rcu_gp_kthread_wake(rsp);
 	WARN_ONCE(rcu_segcblist_n_cbs(&rdp->cblist) != 0 ||
 		  !rcu_segcblist_empty(&rdp->cblist),
 		  "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, 1stCB=%p\n",
@@ -4056,7 +3959,7 @@ static void __init rcu_init_one(struct rcu_state *rsp)
 
 	init_swait_queue_head(&rsp->gp_wq);
 	init_swait_queue_head(&rsp->expedited_wq);
-	rnp = rsp->level[rcu_num_lvls - 1];
+	rnp = rcu_first_leaf_node(rsp);
 	for_each_possible_cpu(i) {
 		while (i > rnp->grphi)
 			rnp++;
@@ -4168,6 +4071,7 @@ static void __init rcu_dump_rcu_node_tree(struct rcu_state *rsp)
 }
 
 struct workqueue_struct *rcu_gp_wq;
+struct workqueue_struct *rcu_par_gp_wq;
 
 void __init rcu_init(void)
 {
@@ -4199,6 +4103,8 @@ void __init rcu_init(void)
 	/* Create workqueue for expedited GPs and for Tree SRCU. */
 	rcu_gp_wq = alloc_workqueue("rcu_gp", WQ_MEM_RECLAIM, 0);
 	WARN_ON(!rcu_gp_wq);
+	rcu_par_gp_wq = alloc_workqueue("rcu_par_gp", WQ_MEM_RECLAIM, 0);
+	WARN_ON(!rcu_par_gp_wq);
 }
 
 #include "tree_exp.h"

kernel/rcu/tree.h

@@ -58,6 +58,14 @@ struct rcu_dynticks {
 #endif /* #ifdef CONFIG_RCU_FAST_NO_HZ */
 };
 
+/* Communicate arguments to a workqueue handler. */
+struct rcu_exp_work {
+	smp_call_func_t rew_func;
+	struct rcu_state *rew_rsp;
+	unsigned long rew_s;
+	struct work_struct rew_work;
+};
+
 /* RCU's kthread states for tracing. */
 #define RCU_KTHREAD_STOPPED  0
 #define RCU_KTHREAD_RUNNING  1
@@ -150,15 +158,32 @@ struct rcu_node {
 	struct swait_queue_head nocb_gp_wq[2];
 				/* Place for rcu_nocb_kthread() to wait GP. */
 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
-	int need_future_gp[2];
-				/* Counts of upcoming no-CB GP requests. */
+	u8 need_future_gp[4];	/* Counts of upcoming GP requests. */
 	raw_spinlock_t fqslock ____cacheline_internodealigned_in_smp;
 
 	spinlock_t exp_lock ____cacheline_internodealigned_in_smp;
 	unsigned long exp_seq_rq;
 	wait_queue_head_t exp_wq[4];
+	struct rcu_exp_work rew;
+	bool exp_need_flush;	/* Need to flush workitem? */
 } ____cacheline_internodealigned_in_smp;
 
+/* Accessors for ->need_future_gp[] array. */
+#define need_future_gp_mask() \
+	(ARRAY_SIZE(((struct rcu_node *)NULL)->need_future_gp) - 1)
+#define need_future_gp_element(rnp, c) \
+	((rnp)->need_future_gp[(c) & need_future_gp_mask()])
+#define need_any_future_gp(rnp)						\
+({									\
+	int __i;							\
+	bool __nonzero = false;						\
+									\
+	for (__i = 0; __i < ARRAY_SIZE((rnp)->need_future_gp); __i++)	\
+		__nonzero = __nonzero ||				\
+			    READ_ONCE((rnp)->need_future_gp[__i]);	\
+	__nonzero;							\
+})
+
 /*
  * Bitmasks in an rcu_node cover the interval [grplo, grphi] of CPU IDs, and
  * are indexed relative to this interval rather than the global CPU ID space.
@@ -224,10 +249,6 @@ struct rcu_data {
 #ifdef CONFIG_RCU_FAST_NO_HZ
 	struct rcu_head oom_head;
 #endif /* #ifdef CONFIG_RCU_FAST_NO_HZ */
-	atomic_long_t exp_workdone0;	/* # done by workqueue. */
-	atomic_long_t exp_workdone1;	/* # done by others #1. */
-	atomic_long_t exp_workdone2;	/* # done by others #2. */
-	atomic_long_t exp_workdone3;	/* # done by others #3. */
 	int exp_dynticks_snap;		/* Double-check need for IPI. */
 
 	/* 6) Callback offloading. */
@@ -408,7 +429,6 @@ extern struct rcu_state rcu_preempt_state;
 #endif /* #ifdef CONFIG_PREEMPT_RCU */
 
 int rcu_dynticks_snap(struct rcu_dynticks *rdtp);
-bool rcu_eqs_special_set(int cpu);
 
 #ifdef CONFIG_RCU_BOOST
 DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
@@ -438,7 +458,6 @@ static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
 static void invoke_rcu_callbacks_kthread(void);
 static bool rcu_is_callbacks_kthread(void);
 #ifdef CONFIG_RCU_BOOST
-static void rcu_preempt_do_callbacks(void);
 static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
 						 struct rcu_node *rnp);
 #endif /* #ifdef CONFIG_RCU_BOOST */
@@ -454,7 +473,6 @@ static void print_cpu_stall_info_end(void);
 static void zero_cpu_stall_ticks(struct rcu_data *rdp);
 static void increment_cpu_stall_ticks(void);
 static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu);
-static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq);
 static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp);
 static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq);
 static void rcu_init_one_nocb(struct rcu_node *rnp);

kernel/rcu/tree_exp.h

@@ -20,6 +20,8 @@
  * Authors: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
  */
 
+#include <linux/lockdep.h>
+
 /*
  * Record the start of an expedited grace period.
  */
@@ -154,14 +156,34 @@ static void __maybe_unused sync_exp_reset_tree(struct rcu_state *rsp)
  * for the current expedited grace period.  Works only for preemptible
  * RCU -- other RCU implementation use other means.
  *
- * Caller must hold the rcu_state's exp_mutex.
+ * Caller must hold the specificed rcu_node structure's ->lock
  */
 static bool sync_rcu_preempt_exp_done(struct rcu_node *rnp)
 {
+	raw_lockdep_assert_held_rcu_node(rnp);
+
 	return rnp->exp_tasks == NULL &&
 	       READ_ONCE(rnp->expmask) == 0;
 }
 
+/*
+ * Like sync_rcu_preempt_exp_done(), but this function assumes the caller
+ * doesn't hold the rcu_node's ->lock, and will acquire and release the lock
+ * itself
+ */
+static bool sync_rcu_preempt_exp_done_unlocked(struct rcu_node *rnp)
+{
+	unsigned long flags;
+	bool ret;
+
+	raw_spin_lock_irqsave_rcu_node(rnp, flags);
+	ret = sync_rcu_preempt_exp_done(rnp);
+	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+
+	return ret;
+}
+
+
 /*
  * Report the exit from RCU read-side critical section for the last task
  * that queued itself during or before the current expedited preemptible-RCU
@@ -170,8 +192,7 @@ static bool sync_rcu_preempt_exp_done(struct rcu_node *rnp)
  * recursively up the tree.  (Calm down, calm down, we do the recursion
  * iteratively!)
  *
- * Caller must hold the rcu_state's exp_mutex and the specified rcu_node
- * structure's ->lock.
+ * Caller must hold the specified rcu_node structure's ->lock.
  */
 static void __rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
 				 bool wake, unsigned long flags)
@@ -207,8 +228,6 @@ static void __rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
 /*
  * Report expedited quiescent state for specified node.  This is a
  * lock-acquisition wrapper function for __rcu_report_exp_rnp().
- *
- * Caller must hold the rcu_state's exp_mutex.
  */
 static void __maybe_unused rcu_report_exp_rnp(struct rcu_state *rsp,
 					      struct rcu_node *rnp, bool wake)
@@ -221,8 +240,7 @@ static void __maybe_unused rcu_report_exp_rnp(struct rcu_state *rsp,
 
 /*
  * Report expedited quiescent state for multiple CPUs, all covered by the
- * specified leaf rcu_node structure.  Caller must hold the rcu_state's
- * exp_mutex.
+ * specified leaf rcu_node structure.
  */
 static void rcu_report_exp_cpu_mult(struct rcu_state *rsp, struct rcu_node *rnp,
 				    unsigned long mask, bool wake)
@@ -248,14 +266,12 @@ static void rcu_report_exp_rdp(struct rcu_state *rsp, struct rcu_data *rdp,
 }
 
 /* Common code for synchronize_{rcu,sched}_expedited() work-done checking. */
-static bool sync_exp_work_done(struct rcu_state *rsp, atomic_long_t *stat,
-			       unsigned long s)
+static bool sync_exp_work_done(struct rcu_state *rsp, unsigned long s)
 {
 	if (rcu_exp_gp_seq_done(rsp, s)) {
 		trace_rcu_exp_grace_period(rsp->name, s, TPS("done"));
 		/* Ensure test happens before caller kfree(). */
 		smp_mb__before_atomic(); /* ^^^ */
-		atomic_long_inc(stat);
 		return true;
 	}
 	return false;
@@ -289,7 +305,7 @@ static bool exp_funnel_lock(struct rcu_state *rsp, unsigned long s)
 	 * promoting locality and is not strictly needed for correctness.
 	 */
 	for (; rnp != NULL; rnp = rnp->parent) {
-		if (sync_exp_work_done(rsp, &rdp->exp_workdone1, s))
+		if (sync_exp_work_done(rsp, s))
 			return true;
 
 		/* Work not done, either wait here or go up. */
@@ -302,8 +318,7 @@ static bool exp_funnel_lock(struct rcu_state *rsp, unsigned long s)
 						  rnp->grplo, rnp->grphi,
 						  TPS("wait"));
 			wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
-				   sync_exp_work_done(rsp,
-						      &rdp->exp_workdone2, s));
+				   sync_exp_work_done(rsp, s));
 			return true;
 		}
 		rnp->exp_seq_rq = s; /* Followers can wait on us. */
@@ -313,7 +328,7 @@ static bool exp_funnel_lock(struct rcu_state *rsp, unsigned long s)
 	}
 	mutex_lock(&rsp->exp_mutex);
 fastpath:
-	if (sync_exp_work_done(rsp, &rdp->exp_workdone3, s)) {
+	if (sync_exp_work_done(rsp, s)) {
 		mutex_unlock(&rsp->exp_mutex);
 		return true;
 	}
@@ -362,23 +377,23 @@ static void sync_sched_exp_online_cleanup(int cpu)
 }
 
 /*
- * Select the nodes that the upcoming expedited grace period needs
- * to wait for.
+ * Select the CPUs within the specified rcu_node that the upcoming
+ * expedited grace period needs to wait for.
  */
-static void sync_rcu_exp_select_cpus(struct rcu_state *rsp,
-				     smp_call_func_t func)
+static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
 {
 	int cpu;
 	unsigned long flags;
+	smp_call_func_t func;
 	unsigned long mask_ofl_test;
 	unsigned long mask_ofl_ipi;
 	int ret;
-	struct rcu_node *rnp;
+	struct rcu_exp_work *rewp =
+		container_of(wp, struct rcu_exp_work, rew_work);
+	struct rcu_node *rnp = container_of(rewp, struct rcu_node, rew);
+	struct rcu_state *rsp = rewp->rew_rsp;
 
-	trace_rcu_exp_grace_period(rsp->name, rcu_exp_gp_seq_endval(rsp), TPS("reset"));
-	sync_exp_reset_tree(rsp);
-	trace_rcu_exp_grace_period(rsp->name, rcu_exp_gp_seq_endval(rsp), TPS("select"));
-	rcu_for_each_leaf_node(rsp, rnp) {
+	func = rewp->rew_func;
 	raw_spin_lock_irqsave_rcu_node(rnp, flags);
 
 	/* Each pass checks a CPU for identity, offline, and idle. */
@@ -404,8 +419,8 @@ static void sync_rcu_exp_select_cpus(struct rcu_state *rsp,
 
 	/*
 	 * Need to wait for any blocked tasks as well.	Note that
-		 * additional blocking tasks will also block the expedited
-		 * GP until such time as the ->expmask bits are cleared.
+	 * additional blocking tasks will also block the expedited GP
+	 * until such time as the ->expmask bits are cleared.
 	 */
 	if (rcu_preempt_has_tasks(rnp))
 		rnp->exp_tasks = rnp->blkd_tasks.next;
@@ -448,7 +463,43 @@ static void sync_rcu_exp_select_cpus(struct rcu_state *rsp,
 	mask_ofl_test |= mask_ofl_ipi;
 	if (mask_ofl_test)
 		rcu_report_exp_cpu_mult(rsp, rnp, mask_ofl_test, false);
+}
+
+/*
+ * Select the nodes that the upcoming expedited grace period needs
+ * to wait for.
+ */
+static void sync_rcu_exp_select_cpus(struct rcu_state *rsp,
+				     smp_call_func_t func)
+{
+	struct rcu_node *rnp;
+
+	trace_rcu_exp_grace_period(rsp->name, rcu_exp_gp_seq_endval(rsp), TPS("reset"));
+	sync_exp_reset_tree(rsp);
+	trace_rcu_exp_grace_period(rsp->name, rcu_exp_gp_seq_endval(rsp), TPS("select"));
+
+	/* Schedule work for each leaf rcu_node structure. */
+	rcu_for_each_leaf_node(rsp, rnp) {
+		rnp->exp_need_flush = false;
+		if (!READ_ONCE(rnp->expmask))
+			continue; /* Avoid early boot non-existent wq. */
+		rnp->rew.rew_func = func;
+		rnp->rew.rew_rsp = rsp;
+		if (!READ_ONCE(rcu_par_gp_wq) ||
+		    rcu_scheduler_active != RCU_SCHEDULER_RUNNING) {
+			/* No workqueues yet. */
+			sync_rcu_exp_select_node_cpus(&rnp->rew.rew_work);
+			continue;
+		}
+		INIT_WORK(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus);
+		queue_work_on(rnp->grplo, rcu_par_gp_wq, &rnp->rew.rew_work);
+		rnp->exp_need_flush = true;
 	}
+
+	/* Wait for workqueue jobs (if any) to complete. */
+	rcu_for_each_leaf_node(rsp, rnp)
+		if (rnp->exp_need_flush)
+			flush_work(&rnp->rew.rew_work);
 }
 
 static void synchronize_sched_expedited_wait(struct rcu_state *rsp)
@@ -469,9 +520,9 @@ static void synchronize_sched_expedited_wait(struct rcu_state *rsp)
 	for (;;) {
 		ret = swait_event_timeout(
 				rsp->expedited_wq,
-				sync_rcu_preempt_exp_done(rnp_root),
+				sync_rcu_preempt_exp_done_unlocked(rnp_root),
 				jiffies_stall);
-		if (ret > 0 || sync_rcu_preempt_exp_done(rnp_root))
+		if (ret > 0 || sync_rcu_preempt_exp_done_unlocked(rnp_root))
 			return;
 		WARN_ON(ret < 0);  /* workqueues should not be signaled. */
 		if (rcu_cpu_stall_suppress)
@@ -504,7 +555,7 @@ static void synchronize_sched_expedited_wait(struct rcu_state *rsp)
 			rcu_for_each_node_breadth_first(rsp, rnp) {
 				if (rnp == rnp_root)
 					continue; /* printed unconditionally */
-				if (sync_rcu_preempt_exp_done(rnp))
+				if (sync_rcu_preempt_exp_done_unlocked(rnp))
 					continue;
 				pr_cont(" l=%u:%d-%d:%#lx/%c",
 					rnp->level, rnp->grplo, rnp->grphi,
@@ -560,14 +611,6 @@ static void rcu_exp_wait_wake(struct rcu_state *rsp, unsigned long s)
 	mutex_unlock(&rsp->exp_wake_mutex);
 }
 
-/* Let the workqueue handler know what it is supposed to do. */
-struct rcu_exp_work {
-	smp_call_func_t rew_func;
-	struct rcu_state *rew_rsp;
-	unsigned long rew_s;
-	struct work_struct rew_work;
-};
-
 /*
  * Common code to drive an expedited grace period forward, used by
  * workqueues and mid-boot-time tasks.
@@ -633,7 +676,7 @@ static void _synchronize_rcu_expedited(struct rcu_state *rsp,
 	rdp = per_cpu_ptr(rsp->rda, raw_smp_processor_id());
 	rnp = rcu_get_root(rsp);
 	wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
-		   sync_exp_work_done(rsp, &rdp->exp_workdone0, s));
+		   sync_exp_work_done(rsp, s));
 	smp_mb(); /* Workqueue actions happen before return. */
 
 	/* Let the next expedited grace period start. */

kernel/rcu/tree_plugin.h

@@ -182,7 +182,7 @@ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
 
 	raw_lockdep_assert_held_rcu_node(rnp);
 	WARN_ON_ONCE(rdp->mynode != rnp);
-	WARN_ON_ONCE(rnp->level != rcu_num_lvls - 1);
+	WARN_ON_ONCE(!rcu_is_leaf_node(rnp));
 
 	/*
 	 * Decide where to queue the newly blocked task.  In theory,
@@ -383,6 +383,50 @@ static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
 	return rnp->gp_tasks != NULL;
 }
 
+/*
+ * Preemptible RCU implementation for rcu_read_lock().
+ * Just increment ->rcu_read_lock_nesting, shared state will be updated
+ * if we block.
+ */
+void __rcu_read_lock(void)
+{
+	current->rcu_read_lock_nesting++;
+	barrier();  /* critical section after entry code. */
+}
+EXPORT_SYMBOL_GPL(__rcu_read_lock);
+
+/*
+ * Preemptible RCU implementation for rcu_read_unlock().
+ * Decrement ->rcu_read_lock_nesting.  If the result is zero (outermost
+ * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
+ * invoke rcu_read_unlock_special() to clean up after a context switch
+ * in an RCU read-side critical section and other special cases.
+ */
+void __rcu_read_unlock(void)
+{
+	struct task_struct *t = current;
+
+	if (t->rcu_read_lock_nesting != 1) {
+		--t->rcu_read_lock_nesting;
+	} else {
+		barrier();  /* critical section before exit code. */
+		t->rcu_read_lock_nesting = INT_MIN;
+		barrier();  /* assign before ->rcu_read_unlock_special load */
+		if (unlikely(READ_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;
+	}
+#ifdef CONFIG_PROVE_LOCKING
+	{
+		int rrln = READ_ONCE(t->rcu_read_lock_nesting);
+
+		WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
+	}
+#endif /* #ifdef CONFIG_PROVE_LOCKING */
+}
+EXPORT_SYMBOL_GPL(__rcu_read_unlock);
+
 /*
  * Advance a ->blkd_tasks-list pointer to the next entry, instead
  * returning NULL if at the end of the list.
@@ -489,7 +533,7 @@ void rcu_read_unlock_special(struct task_struct *t)
 		rnp = t->rcu_blocked_node;
 		raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
 		WARN_ON_ONCE(rnp != t->rcu_blocked_node);
-		WARN_ON_ONCE(rnp->level != rcu_num_lvls - 1);
+		WARN_ON_ONCE(!rcu_is_leaf_node(rnp));
 		empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);
 		empty_exp = sync_rcu_preempt_exp_done(rnp);
 		smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
@@ -685,15 +729,6 @@ static void rcu_preempt_check_callbacks(void)
 		t->rcu_read_unlock_special.b.need_qs = true;
 }
 
-#ifdef CONFIG_RCU_BOOST
-
-static void rcu_preempt_do_callbacks(void)
-{
-	rcu_do_batch(rcu_state_p, this_cpu_ptr(rcu_data_p));
-}
-
-#endif /* #ifdef CONFIG_RCU_BOOST */
-
 /**
  * call_rcu() - Queue an RCU callback for invocation after a grace period.
  * @head: structure to be used for queueing the RCU updates.
@@ -1140,7 +1175,7 @@ static void rcu_kthread_do_work(void)
 {
 	rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data));
 	rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data));
-	rcu_preempt_do_callbacks();
+	rcu_do_batch(&rcu_preempt_state, this_cpu_ptr(&rcu_preempt_data));
 }
 
 static void rcu_cpu_kthread_setup(unsigned int cpu)
@@ -1607,7 +1642,7 @@ static int rcu_oom_notify(struct notifier_block *self,
 
 	for_each_online_cpu(cpu) {
 		smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
-		cond_resched_rcu_qs();
+		cond_resched_tasks_rcu_qs();
 	}
 
 	/* Unconditionally decrement: no need to wake ourselves up. */
@@ -1780,19 +1815,6 @@ static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
 	swake_up_all(sq);
 }
 
-/*
- * Set the root rcu_node structure's ->need_future_gp field
- * based on the sum of those of all rcu_node structures.  This does
- * double-count the root rcu_node structure's requests, but this
- * is necessary to handle the possibility of a rcu_nocb_kthread()
- * having awakened during the time that the rcu_node structures
- * were being updated for the end of the previous grace period.
- */
-static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
-{
-	rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq;
-}
-
 static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
 {
 	return &rnp->nocb_gp_wq[rnp->completed & 0x1];
@@ -1966,7 +1988,7 @@ static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
 			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
 					    TPS("WakeOvf"));
 		} else {
-			wake_nocb_leader_defer(rdp, RCU_NOCB_WAKE,
+			wake_nocb_leader_defer(rdp, RCU_NOCB_WAKE_FORCE,
 					       TPS("WakeOvfIsDeferred"));
 		}
 		rdp->qlen_last_fqs_check = LONG_MAX / 2;
@@ -2048,7 +2070,8 @@ static void rcu_nocb_wait_gp(struct rcu_data *rdp)
 	struct rcu_node *rnp = rdp->mynode;
 
 	raw_spin_lock_irqsave_rcu_node(rnp, flags);
-	needwake = rcu_start_future_gp(rnp, rdp, &c);
+	c = rcu_cbs_completed(rdp->rsp, rnp);
+	needwake = rcu_start_this_gp(rnp, rdp, c);
 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 	if (needwake)
 		rcu_gp_kthread_wake(rdp->rsp);
@@ -2057,7 +2080,7 @@ static void rcu_nocb_wait_gp(struct rcu_data *rdp)
 	 * Wait for the grace period.  Do so interruptibly to avoid messing
 	 * up the load average.
 	 */
-	trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait"));
+	trace_rcu_this_gp(rnp, rdp, c, TPS("StartWait"));
 	for (;;) {
 		swait_event_interruptible(
 			rnp->nocb_gp_wq[c & 0x1],
@@ -2065,9 +2088,9 @@ static void rcu_nocb_wait_gp(struct rcu_data *rdp)
 		if (likely(d))
 			break;
 		WARN_ON(signal_pending(current));
-		trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait"));
+		trace_rcu_this_gp(rnp, rdp, c, TPS("ResumeWait"));
 	}
-	trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait"));
+	trace_rcu_this_gp(rnp, rdp, c, TPS("EndWait"));
 	smp_mb(); /* Ensure that CB invocation happens after GP end. */
 }
 
@@ -2236,7 +2259,7 @@ static int rcu_nocb_kthread(void *arg)
 				cl++;
 			c++;
 			local_bh_enable();
-			cond_resched_rcu_qs();
+			cond_resched_tasks_rcu_qs();
 			list = next;
 		}
 		trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
@@ -2292,7 +2315,7 @@ static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
 void __init rcu_init_nohz(void)
 {
 	int cpu;
-	bool need_rcu_nocb_mask = true;
+	bool need_rcu_nocb_mask = false;
 	struct rcu_state *rsp;
 
 #if defined(CONFIG_NO_HZ_FULL)
@@ -2315,7 +2338,7 @@ void __init rcu_init_nohz(void)
 #endif /* #if defined(CONFIG_NO_HZ_FULL) */
 
 	if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
-		pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
+		pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");
 		cpumask_and(rcu_nocb_mask, cpu_possible_mask,
 			    rcu_nocb_mask);
 	}
@@ -2495,10 +2518,6 @@ static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
 {
 }
 
-static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
-{
-}
-
 static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
 {
 	return NULL;
@@ -2587,8 +2606,7 @@ static bool rcu_nohz_full_cpu(struct rcu_state *rsp)
 }
 
 /*
- * Bind the grace-period kthread for the sysidle flavor of RCU to the
- * timekeeping CPU.
+ * Bind the RCU grace-period kthreads to the housekeeping CPU.
  */
 static void rcu_bind_gp_kthread(void)
 {

kernel/rcu/update.c

@@ -226,54 +226,6 @@ core_initcall(rcu_set_runtime_mode);
 
 #endif /* #if !defined(CONFIG_TINY_RCU) || defined(CONFIG_SRCU) */
 
-#ifdef CONFIG_PREEMPT_RCU
-
-/*
- * Preemptible RCU implementation for rcu_read_lock().
- * Just increment ->rcu_read_lock_nesting, shared state will be updated
- * if we block.
- */
-void __rcu_read_lock(void)
-{
-	current->rcu_read_lock_nesting++;
-	barrier();  /* critical section after entry code. */
-}
-EXPORT_SYMBOL_GPL(__rcu_read_lock);
-
-/*
- * Preemptible RCU implementation for rcu_read_unlock().
- * Decrement ->rcu_read_lock_nesting.  If the result is zero (outermost
- * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
- * invoke rcu_read_unlock_special() to clean up after a context switch
- * in an RCU read-side critical section and other special cases.
- */
-void __rcu_read_unlock(void)
-{
-	struct task_struct *t = current;
-
-	if (t->rcu_read_lock_nesting != 1) {
-		--t->rcu_read_lock_nesting;
-	} else {
-		barrier();  /* critical section before exit code. */
-		t->rcu_read_lock_nesting = INT_MIN;
-		barrier();  /* assign before ->rcu_read_unlock_special load */
-		if (unlikely(READ_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;
-	}
-#ifdef CONFIG_PROVE_LOCKING
-	{
-		int rrln = READ_ONCE(t->rcu_read_lock_nesting);
-
-		WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
-	}
-#endif /* #ifdef CONFIG_PROVE_LOCKING */
-}
-EXPORT_SYMBOL_GPL(__rcu_read_unlock);
-
-#endif /* #ifdef CONFIG_PREEMPT_RCU */
-
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 static struct lock_class_key rcu_lock_key;
 struct lockdep_map rcu_lock_map =
@@ -624,7 +576,7 @@ EXPORT_SYMBOL_GPL(call_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
+ * cond_resched_tasks_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

kernel/sched/core.c

@@ -5025,20 +5025,6 @@ int __cond_resched_lock(spinlock_t *lock)
 }
 EXPORT_SYMBOL(__cond_resched_lock);
 
-int __sched __cond_resched_softirq(void)
-{
-	BUG_ON(!in_softirq());
-
-	if (should_resched(SOFTIRQ_DISABLE_OFFSET)) {
-		local_bh_enable();
-		preempt_schedule_common();
-		local_bh_disable();
-		return 1;
-	}
-	return 0;
-}
-EXPORT_SYMBOL(__cond_resched_softirq);
-
 /**
  * yield - yield the current processor to other threads.
  *

kernel/softirq.c

@@ -145,8 +145,7 @@ static void __local_bh_enable(unsigned int cnt)
 }
 
 /*
- * Special-case - softirqs can safely be enabled in
- * cond_resched_softirq(), or by __do_softirq(),
+ * Special-case - softirqs can safely be enabled by __do_softirq(),
  * without processing still-pending softirqs:
  */
 void _local_bh_enable(void)

kernel/torture.c

@@ -574,7 +574,7 @@ void stutter_wait(const char *title)
 {
 	int spt;
 
-	cond_resched_rcu_qs();
+	cond_resched_tasks_rcu_qs();
 	spt = READ_ONCE(stutter_pause_test);
 	for (; spt; spt = READ_ONCE(stutter_pause_test)) {
 		if (spt == 1) {

kernel/trace/trace_benchmark.c

@@ -159,13 +159,13 @@ static int benchmark_event_kthread(void *arg)
 		 * wants to run, schedule in, but if the CPU is idle,
 		 * we'll keep burning cycles.
 		 *
-		 * Note the _rcu_qs() version of cond_resched() will
+		 * Note the tasks_rcu_qs() version of cond_resched() will
 		 * notify synchronize_rcu_tasks() that this thread has
 		 * passed a quiescent state for rcu_tasks. Otherwise
 		 * this thread will never voluntarily schedule which would
 		 * block synchronize_rcu_tasks() indefinitely.
 		 */
-		cond_resched();
+		cond_resched_tasks_rcu_qs();
 	}
 
 	return 0;

tools/testing/selftests/rcutorture/bin/kvm-find-errors.sh

+#!/bin/sh
+#
+# Invoke a text editor on all console.log files for all runs with diagnostics,
+# that is, on all such files having a console.log.diags counterpart.
+# Note that both console.log.diags and console.log are passed to the
+# editor (currently defaulting to "vi"), allowing the user to get an
+# idea of what to search for in the console.log file.
+#
+# Usage: kvm-find-errors.sh directory
+#
+# The "directory" above should end with the date/time directory, for example,
+# "tools/testing/selftests/rcutorture/res/2018.02.25-14:27:27".
+
+rundir="${1}"
+if test -z "$rundir" -o ! -d "$rundir"
+then
+	echo Usage: $0 directory
+fi
+editor=${EDITOR-vi}
+
+# Find builds with errors
+files=
+for i in ${rundir}/*/Make.out
+do
+	if egrep -q "error:|warning:" < $i
+	then
+		egrep "error:|warning:" < $i > $i.diags
+		files="$files $i.diags $i"
+	fi
+done
+if test -n "$files"
+then
+	$editor $files
+else
+	echo No build errors.
+fi
+if grep -q -e "--buildonly" < ${rundir}/log
+then
+	echo Build-only run, no console logs to check.
+fi
+
+# Find console logs with errors
+files=
+for i in ${rundir}/*/console.log
+do
+	if test -r $i.diags
+	then
+		files="$files $i.diags $i"
+	fi
+done
+if test -n "$files"
+then
+	$editor $files
+else
+	echo No errors in console logs.
+fi

tools/testing/selftests/rcutorture/bin/kvm-recheck-rcu.sh

@@ -34,11 +34,15 @@ fi
 
 configfile=`echo $i | sed -e 's/^.*\///'`
 ngps=`grep ver: $i/console.log 2> /dev/null | tail -1 | sed -e 's/^.* ver: //' -e 's/ .*$//'`
+stopstate="`grep 'End-test grace-period state: g' $i/console.log 2> /dev/null |
+	    tail -1 | sed -e 's/^\[[ 0-9.]*] //' |
+	    awk '{ print \"[\" $1 \" \" $5 \" \" $6 \" \" $7 \"]\"; }' |
+	    tr -d '\012\015'`"
 if test -z "$ngps"
 then
-	echo "$configfile -------"
+	echo "$configfile ------- " $stopstate
 else
-	title="$configfile ------- $ngps grace periods"
+	title="$configfile ------- $ngps GPs"
 	dur=`sed -e 's/^.* rcutorture.shutdown_secs=//' -e 's/ .*$//' < $i/qemu-cmd 2> /dev/null`
 	if test -z "$dur"
 	then
@@ -46,9 +50,9 @@ else
 	else
 		ngpsps=`awk -v ngps=$ngps -v dur=$dur '
 			BEGIN { print ngps / dur }' < /dev/null`
-		title="$title ($ngpsps per second)"
+		title="$title ($ngpsps/s)"
 	fi
-	echo $title
+	echo $title $stopstate
 	nclosecalls=`grep --binary-files=text 'torture: Reader Batch' $i/console.log | tail -1 | awk '{for (i=NF-8;i<=NF;i++) sum+=$i; } END {print sum}'`
 	if test -z "$nclosecalls"
 	then

tools/testing/selftests/rcutorture/bin/kvm-recheck.sh

@@ -48,10 +48,6 @@ do
 				cat $i/Make.oldconfig.err
 			fi
 			parse-build.sh $i/Make.out $configfile
-			if test "$TORTURE_SUITE" != rcuperf
-			then
-				parse-torture.sh $i/console.log $configfile
-			fi
 			parse-console.sh $i/console.log $configfile
 			if test -r $i/Warnings
 			then

tools/testing/selftests/rcutorture/bin/kvm-test-1-run.sh

@@ -267,5 +267,4 @@ then
 	echo Unknown PID, cannot kill qemu command
 fi
 
-parse-torture.sh $resdir/console.log $title
 parse-console.sh $resdir/console.log $title

tools/testing/selftests/rcutorture/bin/parse-console.sh

@@ -24,57 +24,146 @@
 #
 # Authors: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
 
+T=${TMPDIR-/tmp}/parse-console.sh.$$
 file="$1"
 title="$2"
 
+trap 'rm -f $T.seq $T.diags' 0
+
 . functions.sh
 
+# Check for presence and readability of console output file
+if test -f "$file" -a -r "$file"
+then
+	:
+else
+	echo $title unreadable console output file: $file
+	exit 1
+fi
 if grep -Pq '\x00' < $file
 then
 	print_warning Console output contains nul bytes, old qemu still running?
 fi
-egrep 'Badness|WARNING:|Warn|BUG|===========|Call Trace:|Oops:|detected stalls on CPUs/tasks:|self-detected stall on CPU|Stall ended before state dump start|\?\?\? Writer stall state|rcu_.*kthread starved for' < $file | grep -v 'ODEBUG: ' | grep -v 'Warning: unable to open an initial console' > $1.diags
-if test -s $1.diags
+cat /dev/null > $file.diags
+
+# Check for proper termination, except that rcuperf runs don't indicate this.
+if test "$TORTURE_SUITE" != rcuperf
 then
-	print_warning Assertion failure in $file $title
-	# cat $1.diags
+	# check for abject failure
+
+	if grep -q FAILURE $file || grep -q -e '-torture.*!!!' $file
+	then
+		nerrs=`grep --binary-files=text '!!!' $file |
+		tail -1 |
+		awk '
+		{
+			for (i=NF-8;i<=NF;i++)
+				sum+=$i;
+		}
+		END { print sum }'`
+		print_bug $title FAILURE, $nerrs instances
+		exit
+	fi
+
+	grep --binary-files=text 'torture:.*ver:' $file |
+	egrep --binary-files=text -v '\(null\)|rtc: 000000000* ' |
+	sed -e 's/^(initramfs)[^]]*] //' -e 's/^\[[^]]*] //' |
+	awk '
+	BEGIN	{
+		ver = 0;
+		badseq = 0;
+		}
+
+		{
+		if (!badseq && ($5 + 0 != $5 || $5 <= ver)) {
+			badseqno1 = ver;
+			badseqno2 = $5;
+			badseqnr = NR;
+			badseq = 1;
+		}
+		ver = $5
+		}
+
+	END	{
+		if (badseq) {
+			if (badseqno1 == badseqno2 && badseqno2 == ver)
+				print "GP HANG at " ver " torture stat " badseqnr;
+			else
+				print "BAD SEQ " badseqno1 ":" badseqno2 " last:" ver " version " badseqnr;
+		}
+		}' > $T.seq
+
+	if grep -q SUCCESS $file
+	then
+		if test -s $T.seq
+		then
+			print_warning $title `cat $T.seq`
+			echo "   " $file
+			exit 2
+		fi
+	else
+		if grep -q "_HOTPLUG:" $file
+		then
+			print_warning HOTPLUG FAILURES $title `cat $T.seq`
+			echo "   " $file
+			exit 3
+		fi
+		echo $title no success message, `grep --binary-files=text 'ver:' $file | wc -l` successful version messages
+		if test -s $T.seq
+		then
+			print_warning $title `cat $T.seq`
+		fi
+		exit 2
+	fi
+fi | tee -a $file.diags
+
+egrep 'Badness|WARNING:|Warn|BUG|===========|Call Trace:|Oops:|detected stalls on CPUs/tasks:|self-detected stall on CPU|Stall ended before state dump start|\?\?\? Writer stall state|rcu_.*kthread starved for' < $file |
+grep -v 'ODEBUG: ' |
+grep -v 'Warning: unable to open an initial console' > $T.diags
+if test -s $T.diags
+then
+	print_warning "Assertion failure in $file $title"
+	# cat $T.diags
 	summary=""
-	n_badness=`grep -c Badness $1`
+	n_badness=`grep -c Badness $file`
 	if test "$n_badness" -ne 0
 	then
 		summary="$summary  Badness: $n_badness"
 	fi
-	n_warn=`grep -v 'Warning: unable to open an initial console' $1 | egrep -c 'WARNING:|Warn'`
+	n_warn=`grep -v 'Warning: unable to open an initial console' $file | egrep -c 'WARNING:|Warn'`
 	if test "$n_warn" -ne 0
 	then
 		summary="$summary  Warnings: $n_warn"
 	fi
-	n_bugs=`egrep -c 'BUG|Oops:' $1`
+	n_bugs=`egrep -c 'BUG|Oops:' $file`
 	if test "$n_bugs" -ne 0
 	then
 		summary="$summary  Bugs: $n_bugs"
 	fi
-	n_calltrace=`grep -c 'Call Trace:' $1`
+	n_calltrace=`grep -c 'Call Trace:' $file`
 	if test "$n_calltrace" -ne 0
 	then
 		summary="$summary  Call Traces: $n_calltrace"
 	fi
-	n_lockdep=`grep -c =========== $1`
+	n_lockdep=`grep -c =========== $file`
 	if test "$n_badness" -ne 0
 	then
 		summary="$summary  lockdep: $n_badness"
 	fi
-	n_stalls=`egrep -c 'detected stalls on CPUs/tasks:|self-detected stall on CPU|Stall ended before state dump start|\?\?\? Writer stall state' $1`
+	n_stalls=`egrep -c 'detected stalls on CPUs/tasks:|self-detected stall on CPU|Stall ended before state dump start|\?\?\? Writer stall state' $file`
 	if test "$n_stalls" -ne 0
 	then
 		summary="$summary  Stalls: $n_stalls"
 	fi
-	n_starves=`grep -c 'rcu_.*kthread starved for' $1`
+	n_starves=`grep -c 'rcu_.*kthread starved for' $file`
 	if test "$n_starves" -ne 0
 	then
 		summary="$summary  Starves: $n_starves"
 	fi
 	print_warning Summary: $summary
-else
-	rm $1.diags
+	cat $T.diags >> $file.diags
+fi
+if ! test -s $file.diags
+then
+	rm -f $file.diags
 fi

tools/testing/selftests/rcutorture/bin/parse-torture.sh

-#!/bin/bash
-#
-# Check the console output from a torture run for goodness.
-# The "file" is a pathname on the local system, and "title" is
-# a text string for error-message purposes.
-#
-# The file must contain torture output, but can be interspersed
-# with other dmesg text, as in console-log output.
-#
-# Usage: parse-torture.sh file title
-#
-# This program is free software; you can redistribute it and/or modify
-# it under the terms of the GNU General Public License as published by
-# the Free Software Foundation; either version 2 of the License, or
-# (at your option) any later version.
-#
-# This program is distributed in the hope that it will be useful,
-# but WITHOUT ANY WARRANTY; without even the implied warranty of
-# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-# GNU General Public License for more details.
-#
-# You should have received a copy of the GNU General Public License
-# along with this program; if not, you can access it online at
-# http://www.gnu.org/licenses/gpl-2.0.html.
-#
-# Copyright (C) IBM Corporation, 2011
-#
-# Authors: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
-
-T=${TMPDIR-/tmp}/parse-torture.sh.$$
-file="$1"
-title="$2"
-
-trap 'rm -f $T.seq' 0
-
-. functions.sh
-
-# check for presence of torture output file.
-
-if test -f "$file" -a -r "$file"
-then
-	:
-else
-	echo $title unreadable torture output file: $file
-	exit 1
-fi
-
-# check for abject failure
-
-if grep -q FAILURE $file || grep -q -e '-torture.*!!!' $file
-then
-	nerrs=`grep --binary-files=text '!!!' $file | tail -1 | awk '{for (i=NF-8;i<=NF;i++) sum+=$i; } END {print sum}'`
-	print_bug $title FAILURE, $nerrs instances
-	echo "   " $url
-	exit
-fi
-
-grep --binary-files=text 'torture:.*ver:' $file | egrep --binary-files=text -v '\(null\)|rtc: 000000000* ' | sed -e 's/^(initramfs)[^]]*] //' -e 's/^\[[^]]*] //' |
-awk '
-BEGIN	{
-	ver = 0;
-	badseq = 0;
-	}
-
-	{
-	if (!badseq && ($5 + 0 != $5 || $5 <= ver)) {
-		badseqno1 = ver;
-		badseqno2 = $5;
-		badseqnr = NR;
-		badseq = 1;
-	}
-	ver = $5
-	}
-
-END	{
-	if (badseq) {
-		if (badseqno1 == badseqno2 && badseqno2 == ver)
-			print "GP HANG at " ver " torture stat " badseqnr;
-		else
-			print "BAD SEQ " badseqno1 ":" badseqno2 " last:" ver " version " badseqnr;
-	}
-	}' > $T.seq
-
-if grep -q SUCCESS $file
-then
-	if test -s $T.seq
-	then
-		print_warning $title $title `cat $T.seq`
-		echo "   " $file
-		exit 2
-	fi
-else
-	if grep -q "_HOTPLUG:" $file
-	then
-		print_warning HOTPLUG FAILURES $title `cat $T.seq`
-		echo "   " $file
-		exit 3
-	fi
-	echo $title no success message, `grep --binary-files=text 'ver:' $file | wc -l` successful version messages
-	if test -s $T.seq
-	then
-		print_warning $title `cat $T.seq`
-	fi
-	exit 2
-fi