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

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Message-ID: <20141211105647.4e3a25d8@thinkpad-w530>
Date:	Thu, 11 Dec 2014 10:56:47 +0100
From:	David Hildenbrand <dahi@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	linux-kernel@...r.kernel.org, heiko.carstens@...ibm.com,
	borntraeger@...ibm.com, rafael.j.wysocki@...el.com,
	paulmck@...ux.vnet.ibm.com, peterz@...radead.org, bp@...e.de,
	jkosina@...e.cz
Subject: Re: [PATCH v4] CPU hotplug: active_writer not woken up in some
 cases - deadlock

> 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.
> 

Just checked wait_event(). It is safe against such race conditions as the same
pattern is used is applied internally.

Thanks!

David

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