This is a note to let you know that I've just added the patch titled
hrtimers: Push pending hrtimers away from outgoing CPU earlier
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
hrtimers-push-pending-hrtimers-away-from-outgoing-cp.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 052a7117914ed4824dda3350818af593662d07ca
Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Date: Tue Nov 7 15:57:13 2023 +0100
hrtimers: Push pending hrtimers away from outgoing CPU earlier
[ Upstream commit 5c0930ccaad5a74d74e8b18b648c5eb21ed2fe94 ]
2b8272ff4a70 ("cpu/hotplug: Prevent self deadlock on CPU hot-unplug")
solved the straight forward CPU hotplug deadlock vs. the scheduler
bandwidth timer. Yu discovered a more involved variant where a task which
has a bandwidth timer started on the outgoing CPU holds a lock and then
gets throttled. If the lock required by one of the CPU hotplug callbacks
the hotplug operation deadlocks because the unthrottling timer event is not
handled on the dying CPU and can only be recovered once the control CPU
reaches the hotplug state which pulls the pending hrtimers from the dead
CPU.
Solve this by pushing the hrtimers away from the dying CPU in the dying
callbacks. Nothing can queue a hrtimer on the dying CPU at that point because
all other CPUs spin in stop_machine() with interrupts disabled and once the
operation is finished the CPU is marked offline.
Reported-by: Yu Liao <liaoyu15@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Liu Tie <liutie4@xxxxxxxxxx>
Link: https://lore.kernel.org/r/87a5rphara.ffs@tglx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index 71a0a5ffdbb1a..dd9f035be63f7 100644
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -139,6 +139,7 @@ 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 542b4fa2cda9b..3bdaa92a2cab3 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -508,9 +508,9 @@ extern void sysrq_timer_list_show(void);
int hrtimers_prepare_cpu(unsigned int cpu);
#ifdef CONFIG_HOTPLUG_CPU
-int hrtimers_dead_cpu(unsigned int cpu);
+int hrtimers_cpu_dying(unsigned int cpu);
#else
-#define hrtimers_dead_cpu NULL
+#define hrtimers_cpu_dying NULL
#endif
#endif
diff --git a/kernel/cpu.c b/kernel/cpu.c
index c9ca190ec0347..34c09c3d37bc6 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1418,7 +1418,7 @@ static struct cpuhp_step cpuhp_hp_states[] = {
[CPUHP_HRTIMERS_PREPARE] = {
.name = "hrtimers:prepare",
.startup.single = hrtimers_prepare_cpu,
- .teardown.single = hrtimers_dead_cpu,
+ .teardown.single = NULL,
},
[CPUHP_SMPCFD_PREPARE] = {
.name = "smpcfd:prepare",
@@ -1485,6 +1485,12 @@ 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 8512f06f0ebef..bf74f43e42af0 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1922,29 +1922,22 @@ static void migrate_hrtimer_list(struct hrtimer_clock_base *old_base,
}
}
-int hrtimers_dead_cpu(unsigned int scpu)
+int hrtimers_cpu_dying(unsigned int dying_cpu)
{
struct hrtimer_cpu_base *old_base, *new_base;
- int i;
+ int i, ncpu = cpumask_first(cpu_active_mask);
- BUG_ON(cpu_online(scpu));
- tick_cancel_sched_timer(scpu);
+ tick_cancel_sched_timer(dying_cpu);
+
+ old_base = this_cpu_ptr(&hrtimer_bases);
+ new_base = &per_cpu(hrtimer_bases, ncpu);
- /*
- * 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(&new_base->lock);
- raw_spin_lock_nested(&old_base->lock, SINGLE_DEPTH_NESTING);
+ raw_spin_lock(&old_base->lock);
+ raw_spin_lock_nested(&new_base->lock, SINGLE_DEPTH_NESTING);
for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) {
migrate_hrtimer_list(&old_base->clock_base[i],
@@ -1955,15 +1948,13 @@ int hrtimers_dead_cpu(unsigned int scpu)
* The migration might have changed the first expiring softirq
* timer on this CPU. Update it.
*/
- hrtimer_update_softirq_timer(new_base, false);
+ __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);
- raw_spin_unlock(&old_base->lock);
raw_spin_unlock(&new_base->lock);
+ raw_spin_unlock(&old_base->lock);
- /* Check, if we got expired work to do */
- __hrtimer_peek_ahead_timers();
- local_irq_enable();
- local_bh_enable();
return 0;
}
