1 files changed, 144 insertions, 51 deletions

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index c569da65b421..4cd170b2d655 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -24,11 +24,12 @@ static bool rcu_rdp_is_offloaded(struct rcu_data *rdp)
 	 * timers have their own means of synchronization against the
 	 * offloaded state updaters.
 	 */
-	RCU_LOCKDEP_WARN(
+	RCU_NOCB_LOCKDEP_WARN(
 		!(lockdep_is_held(&rcu_state.barrier_mutex) ||
 		  (IS_ENABLED(CONFIG_HOTPLUG_CPU) && lockdep_is_cpus_held()) ||
-		  rcu_lockdep_is_held_nocb(rdp) ||
-		  (!(IS_ENABLED(CONFIG_PREEMPT_COUNT) && preemptible()) &&
+		  lockdep_is_held(&rdp->nocb_lock) ||
+		  lockdep_is_held(&rcu_state.nocb_mutex) ||
+		  ((!(IS_ENABLED(CONFIG_PREEMPT_COUNT) && preemptible()) || softirq_count()) &&
 		   rdp == this_cpu_ptr(&rcu_data)) ||
 		  rcu_current_is_nocb_kthread(rdp)),
 		"Unsafe read of RCU_NOCB offloaded state"
@@ -182,9 +183,9 @@ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
 	switch (blkd_state) {
 	case 0:
 	case                RCU_EXP_TASKS:
-	case                RCU_EXP_TASKS + RCU_GP_BLKD:
+	case                RCU_EXP_TASKS | RCU_GP_BLKD:
 	case RCU_GP_TASKS:
-	case RCU_GP_TASKS + RCU_EXP_TASKS:
+	case RCU_GP_TASKS | RCU_EXP_TASKS:
 
 		/*
 		 * Blocking neither GP, or first task blocking the normal
@@ -197,10 +198,10 @@ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
 
 	case                                              RCU_EXP_BLKD:
 	case                                RCU_GP_BLKD:
-	case                                RCU_GP_BLKD + RCU_EXP_BLKD:
-	case RCU_GP_TASKS +                               RCU_EXP_BLKD:
-	case RCU_GP_TASKS +                 RCU_GP_BLKD + RCU_EXP_BLKD:
-	case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
+	case                                RCU_GP_BLKD | RCU_EXP_BLKD:
+	case RCU_GP_TASKS |                               RCU_EXP_BLKD:
+	case RCU_GP_TASKS |                 RCU_GP_BLKD | RCU_EXP_BLKD:
+	case RCU_GP_TASKS | RCU_EXP_TASKS | RCU_GP_BLKD | RCU_EXP_BLKD:
 
 		/*
 		 * First task arriving that blocks either GP, or first task
@@ -213,9 +214,9 @@ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
 		list_add_tail(&t->rcu_node_entry, &rnp->blkd_tasks);
 		break;
 
-	case                RCU_EXP_TASKS +               RCU_EXP_BLKD:
-	case                RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
-	case RCU_GP_TASKS + RCU_EXP_TASKS +               RCU_EXP_BLKD:
+	case                RCU_EXP_TASKS |               RCU_EXP_BLKD:
+	case                RCU_EXP_TASKS | RCU_GP_BLKD | RCU_EXP_BLKD:
+	case RCU_GP_TASKS | RCU_EXP_TASKS |               RCU_EXP_BLKD:
 
 		/*
 		 * Second or subsequent task blocking the expedited GP.
@@ -226,8 +227,8 @@ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
 		list_add(&t->rcu_node_entry, rnp->exp_tasks);
 		break;
 
-	case RCU_GP_TASKS +                 RCU_GP_BLKD:
-	case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD:
+	case RCU_GP_TASKS |                 RCU_GP_BLKD:
+	case RCU_GP_TASKS | RCU_EXP_TASKS | RCU_GP_BLKD:
 
 		/*
 		 * Second or subsequent task blocking the normal GP.
@@ -274,6 +275,7 @@ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
 		rcu_report_exp_rdp(rdp);
 	else
 		WARN_ON_ONCE(rdp->cpu_no_qs.b.exp);
+	ASSERT_EXCLUSIVE_WRITER_SCOPED(rdp->cpu_no_qs.b.exp);
 }
 
 /*
@@ -484,13 +486,16 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
 	struct rcu_node *rnp;
 	union rcu_special special;
 
+	rdp = this_cpu_ptr(&rcu_data);
+	if (rdp->defer_qs_iw_pending == DEFER_QS_PENDING)
+		rdp->defer_qs_iw_pending = DEFER_QS_IDLE;
+
 	/*
 	 * If RCU core is waiting for this CPU to exit its critical section,
 	 * report the fact that it has exited.  Because irqs are disabled,
 	 * t->rcu_read_unlock_special cannot change.
 	 */
 	special = t->rcu_read_unlock_special;
-	rdp = this_cpu_ptr(&rcu_data);
 	if (!special.s && !rdp->cpu_no_qs.b.exp) {
 		local_irq_restore(flags);
 		return;
@@ -532,7 +537,6 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
 		WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq &&
 			     (!empty_norm || rnp->qsmask));
 		empty_exp = sync_rcu_exp_done(rnp);
-		smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
 		np = rcu_next_node_entry(t, rnp);
 		list_del_init(&t->rcu_node_entry);
 		t->rcu_blocked_node = NULL;
@@ -622,10 +626,98 @@ notrace void rcu_preempt_deferred_qs(struct task_struct *t)
  */
 static void rcu_preempt_deferred_qs_handler(struct irq_work *iwp)
 {
+	unsigned long flags;
 	struct rcu_data *rdp;
 
 	rdp = container_of(iwp, struct rcu_data, defer_qs_iw);
-	rdp->defer_qs_iw_pending = false;
+	local_irq_save(flags);
+
+	/*
+	 * If the IRQ work handler happens to run in the middle of RCU read-side
+	 * critical section, it could be ineffective in getting the scheduler's
+	 * attention to report a deferred quiescent state (the whole point of the
+	 * IRQ work). For this reason, requeue the IRQ work.
+	 *
+	 * Basically, we want to avoid following situation:
+	 * 1. rcu_read_unlock() queues IRQ work (state -> DEFER_QS_PENDING)
+	 * 2. CPU enters new rcu_read_lock()
+	 * 3. IRQ work runs but cannot report QS due to rcu_preempt_depth() > 0
+	 * 4. rcu_read_unlock() does not re-queue work (state still PENDING)
+	 * 5. Deferred QS reporting does not happen.
+	 */
+	if (rcu_preempt_depth() > 0)
+		WRITE_ONCE(rdp->defer_qs_iw_pending, DEFER_QS_IDLE);
+
+	local_irq_restore(flags);
+}
+
+/*
+ * Check if expedited grace period processing during unlock is needed.
+ *
+ * This function determines whether expedited handling is required based on:
+ * 1. Task blocking an expedited grace period (based on a heuristic, could be
+ *    false-positive, see below.)
+ * 2. CPU participating in an expedited grace period
+ * 3. Strict grace period mode requiring expedited handling
+ * 4. RCU priority deboosting needs when interrupts were disabled
+ *
+ * @t: The task being checked
+ * @rdp: The per-CPU RCU data
+ * @rnp: The RCU node for this CPU
+ * @irqs_were_disabled: Whether interrupts were disabled before rcu_read_unlock()
+ *
+ * Returns true if expedited processing of the rcu_read_unlock() is needed.
+ */
+static bool rcu_unlock_needs_exp_handling(struct task_struct *t,
+				      struct rcu_data *rdp,
+				      struct rcu_node *rnp,
+				      bool irqs_were_disabled)
+{
+	/*
+	 * Check if this task is blocking an expedited grace period. If the
+	 * task was preempted within an RCU read-side critical section and is
+	 * on the expedited grace period blockers list (exp_tasks), we need
+	 * expedited handling to unblock the expedited GP. This is not an exact
+	 * check because 't' might not be on the exp_tasks list at all - its
+	 * just a fast heuristic that can be false-positive sometimes.
+	 */
+	if (t->rcu_blocked_node && READ_ONCE(t->rcu_blocked_node->exp_tasks))
+		return true;
+
+	/*
+	 * Check if this CPU is participating in an expedited grace period.
+	 * The expmask bitmap tracks which CPUs need to check in for the
+	 * current expedited GP. If our CPU's bit is set, we need expedited
+	 * handling to help complete the expedited GP.
+	 */
+	if (rdp->grpmask & READ_ONCE(rnp->expmask))
+		return true;
+
+	/*
+	 * In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, all grace periods
+	 * are treated as short for testing purposes even if that means
+	 * disturbing the system more. Check if either:
+	 * - This CPU has not yet reported a quiescent state, or
+	 * - This task was preempted within an RCU critical section
+	 * In either case, require expedited handling for strict GP mode.
+	 */
+	if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) &&
+	    ((rdp->grpmask & READ_ONCE(rnp->qsmask)) || t->rcu_blocked_node))
+		return true;
+
+	/*
+	 * RCU priority boosting case: If a task is subject to RCU priority
+	 * boosting and exits an RCU read-side critical section with interrupts
+	 * disabled, we need expedited handling to ensure timely deboosting.
+	 * Without this, a low-priority task could incorrectly run at high
+	 * real-time priority for an extended period degrading real-time
+	 * responsiveness. This applies to all CONFIG_RCU_BOOST=y kernels,
+	 * not just to PREEMPT_RT.
+	 */
+	if (IS_ENABLED(CONFIG_RCU_BOOST) && irqs_were_disabled && t->rcu_blocked_node)
+		return true;
+
+	return false;
 }
 
 /*
@@ -647,18 +739,14 @@ static void rcu_read_unlock_special(struct task_struct *t)
 	local_irq_save(flags);
 	irqs_were_disabled = irqs_disabled_flags(flags);
 	if (preempt_bh_were_disabled || irqs_were_disabled) {
-		bool expboost; // Expedited GP in flight or possible boosting.
+		bool needs_exp; // Expedited handling needed.
 		struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
 		struct rcu_node *rnp = rdp->mynode;
 
-		expboost = (t->rcu_blocked_node && READ_ONCE(t->rcu_blocked_node->exp_tasks)) ||
-			   (rdp->grpmask & READ_ONCE(rnp->expmask)) ||
-			   (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) &&
-			   ((rdp->grpmask & READ_ONCE(rnp->qsmask)) || t->rcu_blocked_node)) ||
-			   (IS_ENABLED(CONFIG_RCU_BOOST) && irqs_were_disabled &&
-			    t->rcu_blocked_node);
+		needs_exp = rcu_unlock_needs_exp_handling(t, rdp, rnp, irqs_were_disabled);
+
 		// Need to defer quiescent state until everything is enabled.
-		if (use_softirq && (in_hardirq() || (expboost && !irqs_were_disabled))) {
+		if (use_softirq && (in_hardirq() || (needs_exp && !irqs_were_disabled))) {
 			// Using softirq, safe to awaken, and either the
 			// wakeup is free or there is either an expedited
 			// GP in flight or a potential need to deboost.
@@ -671,17 +759,11 @@ static void rcu_read_unlock_special(struct task_struct *t)
 			set_tsk_need_resched(current);
 			set_preempt_need_resched();
 			if (IS_ENABLED(CONFIG_IRQ_WORK) && irqs_were_disabled &&
-			    expboost && !rdp->defer_qs_iw_pending && cpu_online(rdp->cpu)) {
+			    needs_exp && rdp->defer_qs_iw_pending != DEFER_QS_PENDING &&
+			    cpu_online(rdp->cpu)) {
 				// Get scheduler to re-evaluate and call hooks.
 				// If !IRQ_WORK, FQS scan will eventually IPI.
-				if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) &&
-				    IS_ENABLED(CONFIG_PREEMPT_RT))
-					rdp->defer_qs_iw = IRQ_WORK_INIT_HARD(
-								rcu_preempt_deferred_qs_handler);
-				else
-					init_irq_work(&rdp->defer_qs_iw,
-						      rcu_preempt_deferred_qs_handler);
-				rdp->defer_qs_iw_pending = true;
+				rdp->defer_qs_iw_pending = DEFER_QS_PENDING;
 				irq_work_queue_on(&rdp->defer_qs_iw, rdp->cpu);
 			}
 		}
@@ -820,6 +902,10 @@ dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
 	}
 }
 
+static void rcu_preempt_deferred_qs_init(struct rcu_data *rdp)
+{
+	rdp->defer_qs_iw = IRQ_WORK_INIT_HARD(rcu_preempt_deferred_qs_handler);
+}
 #else /* #ifdef CONFIG_PREEMPT_RCU */
 
 /*
@@ -831,8 +917,17 @@ void rcu_read_unlock_strict(void)
 {
 	struct rcu_data *rdp;
 
-	if (irqs_disabled() || preempt_count() || !rcu_state.gp_kthread)
+	if (irqs_disabled() || in_atomic_preempt_off() || !rcu_state.gp_kthread)
 		return;
+
+	/*
+	 * rcu_report_qs_rdp() can only be invoked with a stable rdp and
+	 * from the local CPU.
+	 *
+	 * The in_atomic_preempt_off() check ensures that we come here holding
+	 * the last preempt_count (which will get dropped once we return to
+	 * __rcu_read_unlock().
+	 */
 	rdp = this_cpu_ptr(&rcu_data);
 	rdp->cpu_no_qs.b.norm = false;
 	rcu_report_qs_rdp(rdp);
@@ -869,7 +964,7 @@ static void rcu_qs(void)
 
 /*
  * Register an urgently needed quiescent state.  If there is an
- * emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight
+ * emergency, invoke rcu_momentary_eqs() to do a heavy-weight
  * dyntick-idle quiescent state visible to other CPUs, which will in
  * some cases serve for expedited as well as normal grace periods.
  * Either way, register a lightweight quiescent state.
@@ -889,7 +984,7 @@ void rcu_all_qs(void)
 	this_cpu_write(rcu_data.rcu_urgent_qs, false);
 	if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs))) {
 		local_irq_save(flags);
-		rcu_momentary_dyntick_idle();
+		rcu_momentary_eqs();
 		local_irq_restore(flags);
 	}
 	rcu_qs();
@@ -909,7 +1004,7 @@ void rcu_note_context_switch(bool preempt)
 		goto out;
 	this_cpu_write(rcu_data.rcu_urgent_qs, false);
 	if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs)))
-		rcu_momentary_dyntick_idle();
+		rcu_momentary_eqs();
 out:
 	rcu_tasks_qs(current, preempt);
 	trace_rcu_utilization(TPS("End context switch"));
@@ -973,13 +1068,16 @@ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
  */
 static void rcu_flavor_sched_clock_irq(int user)
 {
-	if (user || rcu_is_cpu_rrupt_from_idle()) {
+	if (user || rcu_is_cpu_rrupt_from_idle() ||
+	     (IS_ENABLED(CONFIG_PREEMPT_COUNT) &&
+	      (preempt_count() == HARDIRQ_OFFSET))) {
 
 		/*
 		 * Get here if this CPU took its interrupt from user
-		 * mode or from the idle loop, and if this is not a
-		 * nested interrupt.  In this case, the CPU is in
-		 * a quiescent state, so note it.
+		 * mode, from the idle loop without this being a nested
+		 * interrupt, or while not holding the task preempt count
+		 * (with PREEMPT_COUNT=y). In this case, the CPU is in a
+		 * quiescent state, so note it.
 		 *
 		 * No memory barrier is required here because rcu_qs()
 		 * references only CPU-local variables that other CPUs
@@ -1007,6 +1105,8 @@ dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
 	WARN_ON_ONCE(!list_empty(&rnp->blkd_tasks));
 }
 
+static void rcu_preempt_deferred_qs_init(struct rcu_data *rdp) { }
+
 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
 
 /*
@@ -1216,16 +1316,13 @@ static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
 	raw_spin_lock_irqsave_rcu_node(rnp, flags);
 	rnp->boost_kthread_task = t;
 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+
 	sp.sched_priority = kthread_prio;
 	sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+	rcu_thread_affine_rnp(t, rnp);
 	wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
 }
 
-static struct task_struct *rcu_boost_task(struct rcu_node *rnp)
-{
-	return READ_ONCE(rnp->boost_kthread_task);
-}
-
 #else /* #ifdef CONFIG_RCU_BOOST */
 
 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
@@ -1242,10 +1339,6 @@ static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
 {
 }
 
-static struct task_struct *rcu_boost_task(struct rcu_node *rnp)
-{
-	return NULL;
-}
 #endif /* #else #ifdef CONFIG_RCU_BOOST */
 
 /*