linux-kernel - Re: [PATCH v5] CPU hotplug: active_writer not woken up in some cases

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Message-ID: <20141214192931.GB6372@redhat.com>
Date:	Sun, 14 Dec 2014 20:29:31 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	David Hildenbrand <dahi@...ux.vnet.ibm.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 v5] CPU hotplug: active_writer not woken up in some
	cases - deadlock

On 12/12, David Hildenbrand wrote:
>
>  void get_online_cpus(void)
>  {
> @@ -103,8 +95,7 @@ void get_online_cpus(void)
>  		return;
>  	cpuhp_lock_acquire_read();
>  	mutex_lock(&cpu_hotplug.lock);
> -	apply_puts_pending(65536);
> -	cpu_hotplug.refcount++;
> +	atomic_inc(&cpu_hotplug.refcount);
>  	mutex_unlock(&cpu_hotplug.lock);

I think the patch is fine.

I am wondering if it makes sense to add

	if (atomic_inc_not_zero(&cpu_hotplug.refcount))
		return;

before mutex_lock(). But even if I am right we can do this later.

Oleg.

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