Commit 23dfeae8 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

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
parents c39cbc5b 2b8272ff

kernel/cpu.c

+23 −1
Original line number Diff line number Diff line
@@ -1487,8 +1487,22 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen, 
	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)