linux-kernel - Re: [PATCH V3] workqueue: fix double unlock bug

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Date:	Tue, 15 Apr 2014 10:43:24 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Daeseok Youn <daeseok.youn@...il.com>
Cc:	laijs@...fujitsu.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3] workqueue: fix double unlock bug

On Tue, Apr 15, 2014 at 08:17:43AM +0900, Daeseok Youn wrote:
> 
> Use default pwq when alloc_unbound_pwq() is failed.
> 
> And remove "if" condition for whether "pwq" is same as "wq->dfl_pwq"
> when wq_calc_node_cpumask() returns false and just use "goto use_dfl_pwq"
> 
> Signed-off-by: Daeseok Youn <daeseok.youn@...il.com>

This is an awfully inadequate patch description.  Can you change it to
something like the following?

  workqueue: fix bugs in wq_update_unbound_numa() failure path

  wq_update_unbound_numa() failure path has the following two bugs.

  * alloc_unbound_pwq() is called without holding wq->mutex; however, if
    the allocation fails, it jumps to out_unlock which tries to unlock
    wq->mutex.

  * The function should switch to dfl_pwq on failure but didn't do so
    after alloc_unbound_pwq() failure.

  Fix it by regrabbing wq->mutex and jumping to use_dfl_pwq on
  alloc_unbound_pwq() failure.
      

> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 0ee63af..0679854 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -4087,10 +4087,7 @@ static void wq_update_unbound_numa(struct workqueue_struct *wq, int cpu,
>  		if (cpumask_equal(cpumask, pwq->pool->attrs->cpumask))
>  			goto out_unlock;
>  	} else {
> -		if (pwq == wq->dfl_pwq)
> -			goto out_unlock;
> -		else
> -			goto use_dfl_pwq;
> +		goto use_dfl_pwq;

And please put this in a separate patch.  Patches which are to be
backported through -stable should be minimal.  Also, please update the
comment above to reflect the change.

Thanks.

-- 
tejun
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