linux-kernel - Re: [PATCH] workqueue: fix double unlock bug

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Date:	Mon, 14 Apr 2014 14:50:40 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Daeseok Youn <daeseok.youn@...il.com>
CC:	<tj@...nel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] workqueue: fix double unlock bug

On 04/14/2014 08:58 AM, Daeseok Youn wrote:
> 
> mutex_unlock() and put_pwq_unlocked() do not need to be called
> when alloc_unbound_pwq() is failed.
> 
> Signed-off-by: Daeseok Youn <daeseok.youn@...il.com>
> ---
>  kernel/workqueue.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 0ee63af..e6e9f6a 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -4100,7 +4100,7 @@ static void wq_update_unbound_numa(struct workqueue_struct *wq, int cpu,
>  	if (!pwq) {
>  		pr_warning("workqueue: allocation failed while updating NUMA affinity of \"%s\"\n",
>  			   wq->name);
> -		goto out_unlock;
> +		return;
>  	}
>  
>  	/*


Nice catch!!!

The supposed correct behavior is documented in the head of
this function. We forgot to do it.

 * If NUMA affinity can't be adjusted due to memory allocation failure, it
 * falls back to @wq->dfl_pwq which may not be optimal but is always
 * correct.

Could you use the following code instead of "goto out_unlock":
		mutex_lock(&wq->mutex);
		if (pwq == wq->dfl_pwq)
			goto out_unlock;
		else
			goto use_dfl_pwq;

Correct&BAD. There are two blocks of suck code in this function:
		if (pwq == wq->dfl_pwq)
			goto out_unlock;
		else
			goto use_dfl_pwq;

You can replace both these two blocks code to the following code:
		goto use_dfl_pwq;

The result is the same as before except it adds some small overhead.
I don't care the small overhead in this function.

Thanks
Lai
		
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