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Fix a CPU hotplug related deadlock between the task which initiates

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and controls a CPU hot-unplug operation vs. the CFS bandwidth timer.
 
 Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'smp-urgent-2023-09-02' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull CPU hotplug fix from Ingo Molnar:
 "Fix a CPU hotplug related deadlock between the task which initiates
  and controls a CPU hot-unplug operation vs. the CFS bandwidth timer"

* tag 'smp-urgent-2023-09-02' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  cpu/hotplug: Prevent self deadlock on CPU hot-unplug
This commit is contained in:
Linus Torvalds 2023-09-02 08:58:49 -07:00
commit 23dfeae882
1 changed files with 23 additions and 1 deletions
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24
kernel/cpu.c
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@ -1487,8 +1487,22 @@ out:
return ret;
}
struct cpu_down_work {
unsigned int cpu;
enum cpuhp_state target;
};
static long __cpu_down_maps_locked(void *arg)
{
struct cpu_down_work *work = arg;
return _cpu_down(work->cpu, 0, work->target);
}
static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
{
struct cpu_down_work work = { .cpu = cpu, .target = target, };
/*
* If the platform does not support hotplug, report it explicitly to
* differentiate it from a transient offlining failure.
@ -1497,7 +1511,15 @@ static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
return -EOPNOTSUPP;
if (cpu_hotplug_disabled)
return -EBUSY;
return _cpu_down(cpu, 0, target);
/*
* Ensure that the control task does not run on the to be offlined
* CPU to prevent a deadlock against cfs_b->period_timer.
*/
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);
}
static int cpu_down(unsigned int cpu, enum cpuhp_state target)