1 files changed, 114 insertions, 217 deletions

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index b22d2e1ca5c0..4fccdfa25716 100644
--- a/kernel/rcu/tree.c
+++ b/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);
@@ -711,44 +709,6 @@ static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
 }
 
 /*
- * 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.
  *
@@ -1642,18 +1602,30 @@ static unsigned long rcu_cbs_completed(struct rcu_state *rsp,
 		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.
 	 */
 	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,
-				unsigned long c, const char *s)
+/* 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,
 				      rnp->completed, c, rnp->level,
@@ -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;
-	}
+	struct rcu_state *rsp = rdp->rsp;
+	struct rcu_node *rnp_root;
 
 	/*
-	 * 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.
+	 * 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->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;
+	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);
+		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. */
 	}
 
-	/*
-	 * 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).
-	 */
-	if (rnp != rnp_root)
-		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"));
+	/* If GP already in progress, just leave, otherwise start one. */
+	if (rnp_root->gpnum != rnp_root->completed) {
+		trace_rcu_this_gp(rnp_root, rdp, c, TPS("Startedleafroot"));
 		goto unlock_out;
 	}
-
-	/* 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 (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("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;
 }
 
@@ -1758,16 +1701,16 @@ out:
  * 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,
-			    needmore ? TPS("CleanupMore") : TPS("Cleanup"));
+	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))
@@ -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;
@@ -2147,7 +2091,7 @@ 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);
@@ -2157,21 +2101,25 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
 	}
 	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);
 }
 
@@ -2283,71 +2231,6 @@ 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
  * kthread if another grace period is required.  Whether we wake
@@ -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? */
-	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 (needwake)
-			rcu_gp_kthread_wake(rsp);
-	} else {
-		local_irq_restore(flags);
+	/* No grace period and unregistered callbacks? */
+	if (!rcu_gp_in_progress(rsp) &&
+	    rcu_segcblist_is_enabled(&rdp->cblist)) {
+		local_irq_save(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);
+		}
 	}
 
 	/* 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?  */
@@ -3861,6 +3751,7 @@ 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 +3763,15 @@ 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",
@@ -4168,6 +4062,7 @@ 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 +4094,8 @@ 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"