linux-kernel - Re: [PATCH] workqueue: Fix possible unexpectedly worker wakeup before started

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Message-ID: <530561DF.90304@cn.fujitsu.com>
Date:	Thu, 20 Feb 2014 10:01:03 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Tejun Heo <tj@...nel.org>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] workqueue: Fix possible unexpectedly worker wakeup before
 started

On 02/20/2014 09:50 AM, Lai Jiangshan wrote:
> On 02/20/2014 08:11 AM, Tejun Heo wrote:
>> Hello, Lai.
>>
>> On Wed, Feb 19, 2014 at 11:47:58AM +0800, Lai Jiangshan wrote:
>>> If a worker is wokenup unexpectedly, it will start to work incorretly.
>>> Although it hardly happen, we should catch it and wait for being started
>>> if it does happen.
>>
>> Can this actually happen?  If so, how?
> 
> I don't think it can happen.
> It depends on the system outside of workqueue.
> 
> I'm afraid someone see the task and wake up it.
> workqueue protect itself.

I was extremely nervously, please drop the patch.
I also don't like too much protective code in workqueue.

> 
>>
>>> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
>>> ---
>>>  kernel/workqueue.c |    6 ++++++
>>>  1 files changed, 6 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
>>> index 82ef9f3..bee5fe1 100644
>>> --- a/kernel/workqueue.c
>>> +++ b/kernel/workqueue.c
>>> @@ -2284,6 +2284,12 @@ static int worker_thread(void *__worker)
>>>  	struct worker *worker = __worker;
>>>  	struct worker_pool *pool = worker->pool;
>>>  
>>> +	if (WARN_ON_ONCE(!(worker->flags & WORKER_STARTED))) {
>>
>> And if this is something which can legitimately happen, why are we
>> triggering WARN on it?
> 
> If it happens, it means there is something wrong in the system.
> 
>>
>>> +		/* The worker is wokenup unexpectedly before started */
>>> +		mutex_lock(&pool->manager_mutex);
>>> +		mutex_unlock(&pool->manager_mutex);
>>
>> And what does these mutex cycling achieve (they need comment)?
> 
> Synchronize the manager to finish.
> 
>>
>> Thanks.
>>
> 
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