linux-kernel - Re: [patch, minor] workqueue: consistently use 'err' in __create_workqueue

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Message-ID: <20080729110250.GA177@tv-sign.ru>
Date:	Tue, 29 Jul 2008 15:02:50 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Dmitry Adamushko <dmitry.adamushko@...il.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: [patch, minor]  workqueue: consistently use 'err' in __create_workqueue_key()

On 07/28, Dmitry Adamushko wrote:
> 
> I guess error handling is a bit illogical in __create_workqueue_key()

Please see below,

>  		for_each_possible_cpu(cpu) {
>  			cwq = init_cpu_workqueue(wq, cpu);
> -			if (err || !cpu_online(cpu))
> +			if (!cpu_online(cpu))
>  				continue;
>  			err = create_workqueue_thread(cwq, cpu);
> +			if (err)
> +				break;

This was done on purpose. The code above does init_cpu_workqueue(cpu)
for each possible cpu, even if we fail to create cwq->thread for some
cpu. This way destroy_workqueue() (called below) shouldn't worry about
the partially initialized workqueues.

The patch above should work, but it assumes that destroy_workqueue()
must do nothing with cwq if cwq->thread == NULL, this is not very
robust.

And, more importantly. Let's suppose __create_workqueue_key() does
"break" and drops cpu_add_remove_lock. Then we race with cpu-hotplug
which can hit the uninitialized cwq. This is fixable, but needs other
complication.

Oleg.

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