From c077094653060ee433a89a8f523e0684f6e1ed4b Mon Sep 17 00:00:00 2001
From: Greg Kroah-Hartman <gregkh@google.com>
Date: Mon, 18 Dec 2023 19:17:03 +0000
Subject: [PATCH] Revert "hrtimers: Push pending hrtimers away from outgoing
 CPU earlier"

This reverts commit 75b5016ce325f1ef9c63e5398a1064cf8a7a7354 which is
commit 5c0930ccaad5a74d74e8b18b648c5eb21ed2fe94 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: Ifdc5474de6e7488eb24959df1697b61b2e3e7880
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
---
 include/linux/cpuhotplug.h |  1 -
 include/linux/hrtimer.h    |  4 ++--
 kernel/cpu.c               |  8 +-------
 kernel/time/hrtimer.c      | 33 +++++++++++++++++++++------------
 4 files changed, 24 insertions(+), 22 deletions(-)

diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index 5f27891ace9d..310ecf18a253 100644
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -195,7 +195,6 @@ enum cpuhp_state {
 	CPUHP_AP_ARM_CORESIGHT_CTI_STARTING,
 	CPUHP_AP_ARM64_ISNDEP_STARTING,
 	CPUHP_AP_SMPCFD_DYING,
-	CPUHP_AP_HRTIMERS_DYING,
 	CPUHP_AP_X86_TBOOT_DYING,
 	CPUHP_AP_ARM_CACHE_B15_RAC_DYING,
 	CPUHP_AP_ONLINE,
diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 0186aac0e72c..f5d43920ecd6 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -534,9 +534,9 @@ extern void sysrq_timer_list_show(void);
 
 int hrtimers_prepare_cpu(unsigned int cpu);
 #ifdef CONFIG_HOTPLUG_CPU
-int hrtimers_cpu_dying(unsigned int cpu);
+int hrtimers_dead_cpu(unsigned int cpu);
 #else
-#define hrtimers_cpu_dying	NULL
+#define hrtimers_dead_cpu	NULL
 #endif
 
 #endif
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 551468d9c5a8..0e4d362e9082 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1733,7 +1733,7 @@ static struct cpuhp_step cpuhp_hp_states[] = {
 	[CPUHP_HRTIMERS_PREPARE] = {
 		.name			= "hrtimers:prepare",
 		.startup.single		= hrtimers_prepare_cpu,
-		.teardown.single	= NULL,
+		.teardown.single	= hrtimers_dead_cpu,
 	},
 	[CPUHP_SMPCFD_PREPARE] = {
 		.name			= "smpcfd:prepare",
@@ -1800,12 +1800,6 @@ static struct cpuhp_step cpuhp_hp_states[] = {
 		.startup.single		= NULL,
 		.teardown.single	= smpcfd_dying_cpu,
 	},
-	[CPUHP_AP_HRTIMERS_DYING] = {
-		.name			= "hrtimers:dying",
-		.startup.single		= NULL,
-		.teardown.single	= hrtimers_cpu_dying,
-	},
-
 	/* Entry state on starting. Interrupts enabled from here on. Transient
 	 * state for synchronsization */
 	[CPUHP_AP_ONLINE] = {
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 5561dabc9b22..e4f0e3b0c4f4 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -2216,22 +2216,29 @@ static void migrate_hrtimer_list(struct hrtimer_clock_base *old_base,
 	}
 }
 
-int hrtimers_cpu_dying(unsigned int dying_cpu)
+int hrtimers_dead_cpu(unsigned int scpu)
 {
 	struct hrtimer_cpu_base *old_base, *new_base;
-	int i, ncpu = cpumask_first(cpu_active_mask);
+	int i;
 
-	tick_cancel_sched_timer(dying_cpu);
-
-	old_base = this_cpu_ptr(&hrtimer_bases);
-	new_base = &per_cpu(hrtimer_bases, ncpu);
+	BUG_ON(cpu_online(scpu));
+	tick_cancel_sched_timer(scpu);
 
+	/*
+	 * this BH disable ensures that raise_softirq_irqoff() does
+	 * not wakeup ksoftirqd (and acquire the pi-lock) while
+	 * holding the cpu_base lock
+	 */
+	local_bh_disable();
+	local_irq_disable();
+	old_base = &per_cpu(hrtimer_bases, scpu);
+	new_base = this_cpu_ptr(&hrtimer_bases);
 	/*
 	 * The caller is globally serialized and nobody else
 	 * takes two locks at once, deadlock is not possible.
 	 */
-	raw_spin_lock(&old_base->lock);
-	raw_spin_lock_nested(&new_base->lock, SINGLE_DEPTH_NESTING);
+	raw_spin_lock(&new_base->lock);
+	raw_spin_lock_nested(&old_base->lock, SINGLE_DEPTH_NESTING);
 
 	for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) {
 		migrate_hrtimer_list(&old_base->clock_base[i],
@@ -2242,13 +2249,15 @@ int hrtimers_cpu_dying(unsigned int dying_cpu)
 	 * The migration might have changed the first expiring softirq
 	 * timer on this CPU. Update it.
 	 */
-	__hrtimer_get_next_event(new_base, HRTIMER_ACTIVE_SOFT);
-	/* Tell the other CPU to retrigger the next event */
-	smp_call_function_single(ncpu, retrigger_next_event, NULL, 0);
+	hrtimer_update_softirq_timer(new_base, false);
 
-	raw_spin_unlock(&new_base->lock);
 	raw_spin_unlock(&old_base->lock);
+	raw_spin_unlock(&new_base->lock);
 
+	/* Check, if we got expired work to do */
+	__hrtimer_peek_ahead_timers();
+	local_irq_enable();
+	local_bh_enable();
 	return 0;
 }