linux-kernel - In function cpu_stop_cpu_callback, BUG_ON(stopper->thread || stopper->enabled || !list_empty(&stopper->works)) is triggered while restarting sometimes.

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Date:	Fri, 3 Aug 2012 01:13:03 +0800
From:	chpoph <chpoph@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: In function cpu_stop_cpu_callback, BUG_ON(stopper->thread ||
 stopper->enabled || !list_empty(&stopper->works)) is triggered while
 restarting sometimes.

In function cpu_stop_cpu_callback, BUG_ON(stopper->thread ||
stopper->enabled || !list_empty(&stopper->works)) is triggered
sometimes.
/* manage stopper for a cpu, mostly lifted from sched migration thread mgmt */
static int __cpuinit cpu_stop_cpu_callback(struct notifier_block *nfb,
                                           unsigned long action, void *hcpu)
{
        ..................................
        switch (action & ~CPU_TASKS_FROZEN) {
        case CPU_UP_PREPARE:
                BUG_ON(stopper->thread || stopper->enabled ||
                       !list_empty(&stopper->works));
         .................................
}

Before actually hardware restarting, machine_restart(cmd) will be called.

void machine_restart(char *cmd)
{
        machine_shutdown();
        arm_pm_restart(reboot_mode, cmd);
        ......................
}

after machine_shutdown(), all other cpus are set offline only by
settting the cpumask. if userspace software which regulators cpu are
running before arm_pm_restart(), it may set set another cpu online and
cpu_up(cpu) is called. At this situation, BUG_ON(stopper->thread ||
stopper->enabled || !list_empty(&stopper->works)) is triggered in
cpu_stop_cpu_callback.

Is it needed to preempt disable before calling machine_shutdown()?
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