From 2c61eff508d6d9601d61e105c452295a7eda1344 Mon Sep 17 00:00:00 2001
From: Greg Kroah-Hartman <gregkh@google.com>
Date: Mon, 18 Dec 2023 18:44:38 +0000
Subject: [PATCH] Revert "hrtimers: Push pending hrtimers away from outgoing
 CPU earlier"

This reverts commit 9a2fc41acb69dd4e2a58d0c04346c3333c2341fc 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 699559b17912..41bd07c5d934 100644
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -145,7 +145,6 @@ enum cpuhp_state {
 	CPUHP_AP_ARM_CORESIGHT_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 d729b12accf6..1e9e5b177519 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -497,9 +497,9 @@ 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 cdc04c7fc412..12292633cfa8 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1464,7 +1464,7 @@ 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",
@@ -1531,12 +1531,6 @@ 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 bf74f43e42af..8512f06f0ebe 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1922,22 +1922,29 @@ 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],
@@ -1948,13 +1955,15 @@ 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;
 }