The way the clockevent devices are finally stopped while a CPU is
offlining is currently chaotic. The layout being by order:
1) tick_sched_timer_dying() stops the tick and the underlying clockevent
but only for oneshot case. The periodic tick and its related
clockevent still runs.
2) tick_broadcast_offline() detaches and stops the per-cpu oneshot
broadcast and append it to the released list.
3) Some individual clockevent drivers stop the clockevents (a second time if
the tick is oneshot)
4) Once the CPU is dead, a control CPU remotely detaches and stops
(a 3rd time if oneshot mode) the CPU clockevent and adds it to the
released list.
5) The released list containing the broadcast device released on step 2)
and the remotely detached clockevent from step 4) are unregistered.
These random events can be factorized if the current clockevent is
detached and stopped by the dying CPU at the generic layer, that is
from the dying CPU:
a) Stop the tick
b) Stop/detach the underlying per-cpu oneshot broadcast clockevent
c) Stop/detach the underlying clockevent
d) Release / unregister the clockevents from b) and c)
e) Release / unregister the remaining clockevents from the dying CPU.
This part could be performed by the dying CPU
This way the drivers and the tick layer don't need to care about
clockevent operations during cpuhotplug down. This also unifies the tick
behaviour on offline CPUs between oneshot and periodic modes, avoiding
offline ticks altogether for sanity.
Adopt the simplification and verify no further clockevent can be
registered for the dying CPU after the final release.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
include/linux/tick.h | 2 --
kernel/cpu.c | 2 --
kernel/time/clockevents.c | 33 ++++++++++++++-------------------
3 files changed, 14 insertions(+), 23 deletions(-)
diff --git a/include/linux/tick.h b/include/linux/tick.h
index 72744638c5b0..b0c74bfe0600 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -20,12 +20,10 @@ extern void __init tick_init(void);
extern void tick_suspend_local(void);
/* Should be core only, but XEN resume magic and ARM BL switcher require it */
extern void tick_resume_local(void);
-extern void tick_cleanup_dead_cpu(int cpu);
#else /* CONFIG_GENERIC_CLOCKEVENTS */
static inline void tick_init(void) { }
static inline void tick_suspend_local(void) { }
static inline void tick_resume_local(void) { }
-static inline void tick_cleanup_dead_cpu(int cpu) { }
#endif /* !CONFIG_GENERIC_CLOCKEVENTS */
#if defined(CONFIG_GENERIC_CLOCKEVENTS) && defined(CONFIG_HOTPLUG_CPU)
diff --git a/kernel/cpu.c b/kernel/cpu.c
index d293d52a3e00..895f3287e3f3 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1338,8 +1338,6 @@ static int takedown_cpu(unsigned int cpu)
cpuhp_bp_sync_dead(cpu);
- tick_cleanup_dead_cpu(cpu);
-
/*
* Callbacks must be re-integrated right away to the RCU state machine.
* Otherwise an RCU callback could block a further teardown function
diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
index 4af27994db93..4ac562ef7f40 100644
--- a/kernel/time/clockevents.c
+++ b/kernel/time/clockevents.c
@@ -452,6 +452,9 @@ void clockevents_register_device(struct clock_event_device *dev)
{
unsigned long flags;
+ if (WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id())))
+ return;
+
/* Initialize state to DETACHED */
clockevent_set_state(dev, CLOCK_EVT_STATE_DETACHED);
@@ -618,39 +621,30 @@ void clockevents_resume(void)
#ifdef CONFIG_HOTPLUG_CPU
-# ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST
/**
- * tick_offline_cpu - Take CPU out of the broadcast mechanism
+ * tick_offline_cpu - Shutdown all clock events related
+ * to this CPU and take it out of the
+ * broadcast mechanism.
* @cpu: The outgoing CPU
*
- * Called on the outgoing CPU after it took itself offline.
+ * Called by the dying CPU during teardown.
*/
void tick_offline_cpu(unsigned int cpu)
-{
- raw_spin_lock(&clockevents_lock);
- tick_broadcast_offline(cpu);
- raw_spin_unlock(&clockevents_lock);
-}
-# endif
-
-/**
- * tick_cleanup_dead_cpu - Cleanup the tick and clockevents of a dead cpu
- * @cpu: The dead CPU
- */
-void tick_cleanup_dead_cpu(int cpu)
{
struct clock_event_device *dev, *tmp;
- unsigned long flags;
- raw_spin_lock_irqsave(&clockevents_lock, flags);
+ raw_spin_lock(&clockevents_lock);
+ tick_broadcast_offline(cpu);
tick_shutdown(cpu);
+
/*
* Unregister the clock event devices which were
- * released from the users in the notify chain.
+ * released above.
*/
list_for_each_entry_safe(dev, tmp, &clockevents_released, list)
list_del(&dev->list);
+
/*
* Now check whether the CPU has left unused per cpu devices
*/
@@ -662,7 +656,8 @@ void tick_cleanup_dead_cpu(int cpu)
list_del(&dev->list);
}
}
- raw_spin_unlock_irqrestore(&clockevents_lock, flags);
+
+ raw_spin_unlock(&clockevents_lock);
}
#endif
--
2.46.0Hi Frederic,
kernel test robot noticed the following build errors:
[auto build test ERROR on tip/timers/core]
[also build test ERROR on tip/smp/core tegra/for-next linus/master v6.12-rc4 next-20241018]
[cannot apply to tip/timers/nohz daniel-lezcano/clockevents/next]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]
url: https://github.com/intel-lab-lkp/linux/commits/Frederic-Weisbecker/clockevents-Improve-clockevents_notify_released-comment/20241018-010807
base: tip/timers/core
patch link: https://lore.kernel.org/r/20241017165041.6954-3-frederic%40kernel.org
patch subject: [PATCH 02/10] clockevents: Shutdown and unregister current clockevents at CPUHP_AP_TICK_DYING
config: s390-allnoconfig (https://download.01.org/0day-ci/archive/20241021/202410211134.JXHThFcy-lkp@intel.com/config)
compiler: clang version 20.0.0git (https://github.com/llvm/llvm-project bfe84f7085d82d06d61c632a7bad1e692fd159e4)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20241021/202410211134.JXHThFcy-lkp@intel.com/reproduce)
If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202410211134.JXHThFcy-lkp@intel.com/
All errors (new ones prefixed by >>):
In file included from kernel/time/clockevents.c:10:
In file included from include/linux/clockchips.h:14:
In file included from include/linux/clocksource.h:22:
In file included from arch/s390/include/asm/io.h:93:
include/asm-generic/io.h:548:31: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
548 | val = __raw_readb(PCI_IOBASE + addr);
| ~~~~~~~~~~ ^
include/asm-generic/io.h:561:61: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
561 | val = __le16_to_cpu((__le16 __force)__raw_readw(PCI_IOBASE + addr));
| ~~~~~~~~~~ ^
include/uapi/linux/byteorder/big_endian.h:37:59: note: expanded from macro '__le16_to_cpu'
37 | #define __le16_to_cpu(x) __swab16((__force __u16)(__le16)(x))
| ^
include/uapi/linux/swab.h:102:54: note: expanded from macro '__swab16'
102 | #define __swab16(x) (__u16)__builtin_bswap16((__u16)(x))
| ^
In file included from kernel/time/clockevents.c:10:
In file included from include/linux/clockchips.h:14:
In file included from include/linux/clocksource.h:22:
In file included from arch/s390/include/asm/io.h:93:
include/asm-generic/io.h:574:61: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
574 | val = __le32_to_cpu((__le32 __force)__raw_readl(PCI_IOBASE + addr));
| ~~~~~~~~~~ ^
include/uapi/linux/byteorder/big_endian.h:35:59: note: expanded from macro '__le32_to_cpu'
35 | #define __le32_to_cpu(x) __swab32((__force __u32)(__le32)(x))
| ^
include/uapi/linux/swab.h:115:54: note: expanded from macro '__swab32'
115 | #define __swab32(x) (__u32)__builtin_bswap32((__u32)(x))
| ^
In file included from kernel/time/clockevents.c:10:
In file included from include/linux/clockchips.h:14:
In file included from include/linux/clocksource.h:22:
In file included from arch/s390/include/asm/io.h:93:
include/asm-generic/io.h:585:33: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
585 | __raw_writeb(value, PCI_IOBASE + addr);
| ~~~~~~~~~~ ^
include/asm-generic/io.h:595:59: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
595 | __raw_writew((u16 __force)cpu_to_le16(value), PCI_IOBASE + addr);
| ~~~~~~~~~~ ^
include/asm-generic/io.h:605:59: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
605 | __raw_writel((u32 __force)cpu_to_le32(value), PCI_IOBASE + addr);
| ~~~~~~~~~~ ^
include/asm-generic/io.h:693:20: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
693 | readsb(PCI_IOBASE + addr, buffer, count);
| ~~~~~~~~~~ ^
include/asm-generic/io.h:701:20: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
701 | readsw(PCI_IOBASE + addr, buffer, count);
| ~~~~~~~~~~ ^
include/asm-generic/io.h:709:20: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
709 | readsl(PCI_IOBASE + addr, buffer, count);
| ~~~~~~~~~~ ^
include/asm-generic/io.h:718:21: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
718 | writesb(PCI_IOBASE + addr, buffer, count);
| ~~~~~~~~~~ ^
include/asm-generic/io.h:727:21: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
727 | writesw(PCI_IOBASE + addr, buffer, count);
| ~~~~~~~~~~ ^
include/asm-generic/io.h:736:21: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
736 | writesl(PCI_IOBASE + addr, buffer, count);
| ~~~~~~~~~~ ^
In file included from kernel/time/clockevents.c:13:
In file included from include/linux/module.h:19:
In file included from include/linux/elf.h:6:
In file included from arch/s390/include/asm/elf.h:181:
In file included from arch/s390/include/asm/mmu_context.h:11:
In file included from arch/s390/include/asm/pgalloc.h:18:
In file included from include/linux/mm.h:2213:
include/linux/vmstat.h:518:36: warning: arithmetic between different enumeration types ('enum node_stat_item' and 'enum lru_list') [-Wenum-enum-conversion]
518 | return node_stat_name(NR_LRU_BASE + lru) + 3; // skip "nr_"
| ~~~~~~~~~~~ ^ ~~~
>> kernel/time/clockevents.c:632:6: error: redefinition of 'tick_offline_cpu'
632 | void tick_offline_cpu(unsigned int cpu)
| ^
kernel/time/tick-internal.h:148:20: note: previous definition is here
148 | static inline void tick_offline_cpu(unsigned int cpu) { }
| ^
13 warnings and 1 error generated.
vim +/tick_offline_cpu +632 kernel/time/clockevents.c
1b72d43237980e Thomas Gleixner 2019-03-21 623
1b72d43237980e Thomas Gleixner 2019-03-21 624 /**
86e36067908464 Frederic Weisbecker 2024-10-17 625 * tick_offline_cpu - Shutdown all clock events related
86e36067908464 Frederic Weisbecker 2024-10-17 626 * to this CPU and take it out of the
86e36067908464 Frederic Weisbecker 2024-10-17 627 * broadcast mechanism.
1b72d43237980e Thomas Gleixner 2019-03-21 628 * @cpu: The outgoing CPU
1b72d43237980e Thomas Gleixner 2019-03-21 629 *
86e36067908464 Frederic Weisbecker 2024-10-17 630 * Called by the dying CPU during teardown.
1b72d43237980e Thomas Gleixner 2019-03-21 631 */
1b72d43237980e Thomas Gleixner 2019-03-21 @632 void tick_offline_cpu(unsigned int cpu)
d316c57ff6bfad Thomas Gleixner 2007-02-16 633 {
bb6eddf7676e1c Thomas Gleixner 2009-12-10 634 struct clock_event_device *dev, *tmp;
0b858e6ff9a38b Li Zefan 2008-02-08 635
86e36067908464 Frederic Weisbecker 2024-10-17 636 raw_spin_lock(&clockevents_lock);
d316c57ff6bfad Thomas Gleixner 2007-02-16 637
86e36067908464 Frederic Weisbecker 2024-10-17 638 tick_broadcast_offline(cpu);
a49b116dcb1265 Thomas Gleixner 2015-04-03 639 tick_shutdown(cpu);
86e36067908464 Frederic Weisbecker 2024-10-17 640
d316c57ff6bfad Thomas Gleixner 2007-02-16 641 /*
d316c57ff6bfad Thomas Gleixner 2007-02-16 642 * Unregister the clock event devices which were
86e36067908464 Frederic Weisbecker 2024-10-17 643 * released above.
d316c57ff6bfad Thomas Gleixner 2007-02-16 644 */
bb6eddf7676e1c Thomas Gleixner 2009-12-10 645 list_for_each_entry_safe(dev, tmp, &clockevents_released, list)
bb6eddf7676e1c Thomas Gleixner 2009-12-10 646 list_del(&dev->list);
86e36067908464 Frederic Weisbecker 2024-10-17 647
bb6eddf7676e1c Thomas Gleixner 2009-12-10 648 /*
bb6eddf7676e1c Thomas Gleixner 2009-12-10 649 * Now check whether the CPU has left unused per cpu devices
bb6eddf7676e1c Thomas Gleixner 2009-12-10 650 */
bb6eddf7676e1c Thomas Gleixner 2009-12-10 651 list_for_each_entry_safe(dev, tmp, &clockevent_devices, list) {
bb6eddf7676e1c Thomas Gleixner 2009-12-10 652 if (cpumask_test_cpu(cpu, dev->cpumask) &&
ea9d8e3f45404d Xiaotian Feng 2010-01-07 653 cpumask_weight(dev->cpumask) == 1 &&
ea9d8e3f45404d Xiaotian Feng 2010-01-07 654 !tick_is_broadcast_device(dev)) {
472c4a9437d3c6 Viresh Kumar 2015-05-21 655 BUG_ON(!clockevent_state_detached(dev));
bb6eddf7676e1c Thomas Gleixner 2009-12-10 656 list_del(&dev->list);
bb6eddf7676e1c Thomas Gleixner 2009-12-10 657 }
bb6eddf7676e1c Thomas Gleixner 2009-12-10 658 }
86e36067908464 Frederic Weisbecker 2024-10-17 659
86e36067908464 Frederic Weisbecker 2024-10-17 660 raw_spin_unlock(&clockevents_lock);
d316c57ff6bfad Thomas Gleixner 2007-02-16 661 }
a49b116dcb1265 Thomas Gleixner 2015-04-03 662 #endif
501f867064e95f Thomas Gleixner 2013-04-25 663
--
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