Messages in this thread Patch in this message | | | Date | Tue, 17 Oct 2023 17:09:53 +0800 (CST) | From | <> | Subject | [PATCH V2] cpu/hotplug: dont offline the last non-isolated CPU |
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From: Ran Xiaokai <ran.xiaokai@zte.com.cn>
If system has some isolate cpus with "isolcpus=" parameter, and user try to offline all the non-isolated CPUs, kernel will first report a warning and then panic when taking the last non-isolated CPU offline.
When offline the last non-isolate cpu, cpuset_hotplug_workfn() rebuild_sched_domains_locked() ndoms = generate_sched_domains(&doms, &attr); cpumask_and(doms[0], top_cpuset.effective_cpus, housekeeping_cpumask(HK_FLAG_DOMAIN));
As isolated cpus are excluded, "doms" passes to partition_sched_domains_locked() will be an empty cpumask.
WARNING: CPU: 4 PID: 80 at kernel/sched/topology.c:2366 build_sched_domains+0x120c/0x1408 Call trace: build_sched_domains+0x120c/0x1408 partition_sched_domains_locked+0x234/0x880 rebuild_sched_domains_locked+0x37c/0x798 rebuild_sched_domains+0x30/0x58 cpuset_hotplug_workfn+0x2a8/0x930 process_scheduled_works+0x178/0x3e0 worker_thread+0x174/0x2f0 ---[ end trace 0000000000000000 ]--- Unable to handle kernel paging request at virtual address fffe80027ab37080 partition_sched_domains_locked+0x318/0x880 rebuild_sched_domains_locked+0x37c/0x798 rebuild_sched_domains+0x30/0x58 cpuset_hotplug_workfn+0x2a8/0x930 process_scheduled_works+0x178/0x3e0 worker_thread+0x174/0x2f0 kthread+0x10c/0x128 ret_from_fork+0x10/0x20 Code: 1a850042 b9441883 f862dae0 8b000021 (f945003b)
Kernel should not panic when user managing CPUs with this meaningless behavior, so we add a check for this, which prevent user taking the last non-isolated CPU offline.
Signed-off-by: Ran Xiaokai <ran.xiaokai@zte.com.cn> Suggested-by: Thomas Gleixner <tglx@linutronix.de> Cc: Yang Yang <yang.yang29@zte.com.cn> Cc: Xuexin Jiang <jiang.xuexin@zte.com.cn> --- kernel/cpu.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/kernel/cpu.c b/kernel/cpu.c index 6de7c6bb74ee..94430ea8b4a5 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -1515,11 +1515,14 @@ static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target) /* * Ensure that the control task does not run on the to be offlined * CPU to prevent a deadlock against cfs_b->period_timer. + * Also keep at least one housekeeping cpu onlined to avoid generating + * an empty sched_domain span. */ - cpu = cpumask_any_but(cpu_online_mask, cpu); - if (cpu >= nr_cpu_ids) - return -EBUSY; - return work_on_cpu(cpu, __cpu_down_maps_locked, &work); + for_each_cpu_and(cpu, cpu_online_mask, housekeeping_cpumask(HK_TYPE_DOMAIN)) { + if (cpu != work.cpu) + return work_on_cpu(cpu, __cpu_down_maps_locked, &work); + } + return -EBUSY; }
static int cpu_down(unsigned int cpu, enum cpuhp_state target) -- 2.15.2
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