Merge tag 'next.2025.05.17a' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux

Pull RCU updates from Joel Fernandes:
 - Removed swake_up_one_online() workaround
 - Reverted an incorrect rcuog wake-up fix from offline softirq
 - Rust RCU Guard methods marked as inline
 - Updated MAINTAINERS with Joel’s and Zqiang's new email address
 - Replaced magic constant in rcu_seq_done_exact() with named constant
 - Added warning mechanism to validate rcu_seq_done_exact()
 - Switched SRCU polling API to use rcu_seq_done_exact()
 - Commented on redundant delta check in rcu_seq_done_exact()
 - Made ->gpwrap tests in rcutorture more frequent
 - Fixed reuse of ARM64 images in rcutorture
 - rcutorture improved to check Kconfig and reader conflict handling
 - Extracted logic from rcu_torture_one_read() for clarity
 - Updated LWN RCU API documentation links
 - Enabled --do-rt in torture.sh for CONFIG_PREEMPT_RT
 - Added tests for SRCU up/down reader primitives
 - Added comments and delays checks in rcutorture
 - Deprecated srcu_read_lock_lite() and srcu_read_unlock_lite() via checkpatch
 - Added --do-normal and --do-no-normal to torture.sh
 - Added RCU Rust binding tests to torture.sh
 - Reduced CPU overcommit and removed MAXSMP/CPUMASK_OFFSTACK in TREE01
 - Replaced kmalloc() with kcalloc() in rcuscale
 - Refined listRCU example code for stale data elimination
 - Fixed hardirq count bug for x86 in cpu_stall_cputime
 - Added safety checks in rcu/nocb for offloaded rdp access
 - Other miscellaneous changes

* tag 'next.2025.05.17a' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux: (27 commits)
  rcutorture: Fix issue with re-using old images on ARM64
  rcutorture: Remove MAXSMP and CPUMASK_OFFSTACK from TREE01
  rcutorture: Reduce TREE01 CPU overcommit
  torture: Check for "Call trace:" as well as "Call Trace:"
  rcutorture: Perform more frequent testing of ->gpwrap
  torture: Add testing of RCU's Rust bindings to torture.sh
  torture: Add --do-{,no-}normal to torture.sh
  checkpatch: Deprecate srcu_read_lock_lite() and srcu_read_unlock_lite()
  rcutorture: Comment invocations of tick_dep_set_task()
  rcu/nocb: Add Safe checks for access offloaded rdp
  rcuscale: using kcalloc() to relpace kmalloc()
  doc/RCU/listRCU: refine example code for eliminating stale data
  doc: Update LWN RCU API links in whatisRCU.rst
  Revert "rcu/nocb: Fix rcuog wake-up from offline softirq"
  rust: sync: rcu: Mark Guard methods as inline
  rcu/cpu_stall_cputime: fix the hardirq count for x86 architecture
  rcu: Remove swake_up_one_online() bandaid
  MAINTAINERS: Update Zqiang's email address
  rcutorture: Make torture.sh --do-rt use CONFIG_PREEMPT_RT
  srcu: Use rcu_seq_done_exact() for polling API
  ...

1 files changed, 46 insertions, 38 deletions

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 659f83e71048..e8a4b720d7d2 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -80,6 +80,15 @@ static void rcu_sr_normal_gp_cleanup_work(struct work_struct *);
 static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, rcu_data) = {
 	.gpwrap = true,
 };
+
+int rcu_get_gpwrap_count(int cpu)
+{
+	struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+
+	return READ_ONCE(rdp->gpwrap_count);
+}
+EXPORT_SYMBOL_GPL(rcu_get_gpwrap_count);
+
 static struct rcu_state rcu_state = {
 	.level = { &rcu_state.node[0] },
 	.gp_state = RCU_GP_IDLE,
@@ -757,6 +766,25 @@ void rcu_request_urgent_qs_task(struct task_struct *t)
 	smp_store_release(per_cpu_ptr(&rcu_data.rcu_urgent_qs, cpu), true);
 }
 
+static unsigned long seq_gpwrap_lag = ULONG_MAX / 4;
+
+/**
+ * rcu_set_gpwrap_lag - Set RCU GP sequence overflow lag value.
+ * @lag_gps: Set overflow lag to this many grace period worth of counters
+ * which is used by rcutorture to quickly force a gpwrap situation.
+ * @lag_gps = 0 means we reset it back to the boot-time value.
+ */
+void rcu_set_gpwrap_lag(unsigned long lag_gps)
+{
+	unsigned long lag_seq_count;
+
+	lag_seq_count = (lag_gps == 0)
+			? ULONG_MAX / 4
+			: lag_gps << RCU_SEQ_CTR_SHIFT;
+	WRITE_ONCE(seq_gpwrap_lag, lag_seq_count);
+}
+EXPORT_SYMBOL_GPL(rcu_set_gpwrap_lag);
+
 /*
  * When trying to report a quiescent state on behalf of some other CPU,
  * it is our responsibility to check for and handle potential overflow
@@ -767,9 +795,11 @@ void rcu_request_urgent_qs_task(struct task_struct *t)
 static void rcu_gpnum_ovf(struct rcu_node *rnp, struct rcu_data *rdp)
 {
 	raw_lockdep_assert_held_rcu_node(rnp);
-	if (ULONG_CMP_LT(rcu_seq_current(&rdp->gp_seq) + ULONG_MAX / 4,
-			 rnp->gp_seq))
+	if (ULONG_CMP_LT(rcu_seq_current(&rdp->gp_seq) + seq_gpwrap_lag,
+			 rnp->gp_seq)) {
 		WRITE_ONCE(rdp->gpwrap, true);
+		WRITE_ONCE(rdp->gpwrap_count, READ_ONCE(rdp->gpwrap_count) + 1);
+	}
 	if (ULONG_CMP_LT(rdp->rcu_iw_gp_seq + ULONG_MAX / 4, rnp->gp_seq))
 		rdp->rcu_iw_gp_seq = rnp->gp_seq + ULONG_MAX / 4;
 }
@@ -801,6 +831,10 @@ static int rcu_watching_snap_save(struct rcu_data *rdp)
 	return 0;
 }
 
+#ifndef arch_irq_stat_cpu
+#define arch_irq_stat_cpu(cpu) 0
+#endif
+
 /*
  * Returns positive if the specified CPU has passed through a quiescent state
  * by virtue of being in or having passed through an dynticks idle state since
@@ -936,9 +970,9 @@ static int rcu_watching_snap_recheck(struct rcu_data *rdp)
 			rsrp->cputime_irq     = kcpustat_field(kcsp, CPUTIME_IRQ, cpu);
 			rsrp->cputime_softirq = kcpustat_field(kcsp, CPUTIME_SOFTIRQ, cpu);
 			rsrp->cputime_system  = kcpustat_field(kcsp, CPUTIME_SYSTEM, cpu);
-			rsrp->nr_hardirqs = kstat_cpu_irqs_sum(rdp->cpu);
-			rsrp->nr_softirqs = kstat_cpu_softirqs_sum(rdp->cpu);
-			rsrp->nr_csw = nr_context_switches_cpu(rdp->cpu);
+			rsrp->nr_hardirqs = kstat_cpu_irqs_sum(cpu) + arch_irq_stat_cpu(cpu);
+			rsrp->nr_softirqs = kstat_cpu_softirqs_sum(cpu);
+			rsrp->nr_csw = nr_context_switches_cpu(cpu);
 			rsrp->jiffies = jiffies;
 			rsrp->gp_seq = rdp->gp_seq;
 		}
@@ -1060,38 +1094,6 @@ static bool rcu_future_gp_cleanup(struct rcu_node *rnp)
 	return needmore;
 }
 
-static void swake_up_one_online_ipi(void *arg)
-{
-	struct swait_queue_head *wqh = arg;
-
-	swake_up_one(wqh);
-}
-
-static void swake_up_one_online(struct swait_queue_head *wqh)
-{
-	int cpu = get_cpu();
-
-	/*
-	 * If called from rcutree_report_cpu_starting(), wake up
-	 * is dangerous that late in the CPU-down hotplug process. The
-	 * scheduler might queue an ignored hrtimer. Defer the wake up
-	 * to an online CPU instead.
-	 */
-	if (unlikely(cpu_is_offline(cpu))) {
-		int target;
-
-		target = cpumask_any_and(housekeeping_cpumask(HK_TYPE_RCU),
-					 cpu_online_mask);
-
-		smp_call_function_single(target, swake_up_one_online_ipi,
-					 wqh, 0);
-		put_cpu();
-	} else {
-		put_cpu();
-		swake_up_one(wqh);
-	}
-}
-
 /*
  * Awaken the grace-period kthread.  Don't do a self-awaken (unless in an
  * interrupt or softirq handler, in which case we just might immediately
@@ -1116,7 +1118,7 @@ static void rcu_gp_kthread_wake(void)
 		return;
 	WRITE_ONCE(rcu_state.gp_wake_time, jiffies);
 	WRITE_ONCE(rcu_state.gp_wake_seq, READ_ONCE(rcu_state.gp_seq));
-	swake_up_one_online(&rcu_state.gp_wq);
+	swake_up_one(&rcu_state.gp_wq);
 }
 
 /*
@@ -1798,6 +1800,7 @@ static noinline_for_stack bool rcu_gp_init(void)
 	struct rcu_data *rdp;
 	struct rcu_node *rnp = rcu_get_root();
 	bool start_new_poll;
+	unsigned long old_gp_seq;
 
 	WRITE_ONCE(rcu_state.gp_activity, jiffies);
 	raw_spin_lock_irq_rcu_node(rnp);
@@ -1825,7 +1828,12 @@ static noinline_for_stack bool rcu_gp_init(void)
 	 */
 	start_new_poll = rcu_sr_normal_gp_init();
 	/* Record GP times before starting GP, hence rcu_seq_start(). */
+	old_gp_seq = rcu_state.gp_seq;
 	rcu_seq_start(&rcu_state.gp_seq);
+	/* Ensure that rcu_seq_done_exact() guardband doesn't give false positives. */
+	WARN_ON_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) &&
+		     rcu_seq_done_exact(&old_gp_seq, rcu_seq_snap(&rcu_state.gp_seq)));
+
 	ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq);
 	trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("start"));
 	rcu_poll_gp_seq_start(&rcu_state.gp_seq_polled_snap);