Re: [PATCH v4] CPU hotplug: active_writer not woken up in some cases - deadlock

[David Hildenbrand <dahi@linux.vnet.ibm.com>]

> This is subjective, but how about
> 
> 	static bool xxx(void)
> 	{
> 		mutex_lock(&cpu_hotplug.lock);
> 		if (atomic_read(&cpu_hotplug.refcount) == 0)
> 			return true;
> 		mutex_unlock(&cpu_hotplug.lock);
> 		return false;
> 	}
> 
> 	void cpu_hotplug_begin(void)
> 	{
> 		cpu_hotplug.active_writer = current;
> 
> 		cpuhp_lock_acquire();
> 		wait_event(&cpu_hotplug.wq, xxx());
> 	}
> 
> instead?
> 
> Oleg.
> 

[   50.662459] do not call blocking ops when !TASK_RUNNING; state=2 set at [<000000000017340e>] prepare_to_wait_event+0x7a/0x124
[   50.662472] ------------[ cut here ]------------
[   50.662475] WARNING: at kernel/sched/core.c:7301
[   50.662477] Modules linked in:
[   50.662482] CPU: 5 PID: 225 Comm: cpu_start_stop. Not tainted 3.18.0+ #59
[   50.662485] task: 0000000001f94b20 ti: 0000000001ffc000 task.ti: 0000000001ffc000
...

Looks like your suggestion won't work. We can only set the task to
TASK_UNINTERRUPTIBLE after taking the lock.

David