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cpu/hotplug: Don't offline the last non-isolated CPU

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[ Upstream commit 38685e2a04 ]

If a system has isolated CPUs via the "isolcpus=" command line parameter,
then an attempt to offline the last housekeeping CPU will result in a
WARN_ON() when rebuilding the scheduler domains and a subsequent panic due
to and unhandled empty CPU mas in partition_sched_domains_locked().

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));

Thus results in an empty CPU mask which triggers the warning and then the
subsequent crash:

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

Unable to handle kernel paging request at virtual address fffe80027ab37080
 partition_sched_domains_locked+0x318/0x880
 rebuild_sched_domains_locked+0x37c/0x798

Aside of the resulting crash, it does not make any sense to offline the last
last housekeeping CPU.

Prevent this by masking out the non-housekeeping CPUs when selecting a
target CPU for initiating the CPU unplug operation via the work queue.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ran Xiaokai <ran.xiaokai@zte.com.cn>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/202310171709530660462@zte.com.cn
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Ran Xiaokai 2023-10-17 17:09:53 +08:00 committed by Greg Kroah-Hartman
parent f6cc3d85cb
commit 3073f6df78
1 changed files with 7 additions and 4 deletions
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11
kernel/cpu.c
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@ -1523,11 +1523,14 @@ 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)