linux-kernel - Re: [PATCH 05/11 V5] workqueue: Add @bind arguement back without change any thing

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Date:	Fri, 07 Sep 2012 10:11:56 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Tejun Heo <tj@...nel.org>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 05/11 V5] workqueue: Add @bind arguement back without
 change any thing

On 09/07/2012 12:51 AM, Tejun Heo wrote:
> Hello, Lai.
> 
> On Thu, Sep 06, 2012 at 09:04:06AM +0800, Lai Jiangshan wrote:
>>> This doesn't change anything.  You're just moving the test to the
>>> caller with comments there explaining how it won't change even if
>>> gcwq->lock is released.  It seems more confusing to me.  The flag is
>>> still protected by manager_mutex.  How is this an improvement?
>>>
>>
>> Some other bit of gcwq->flags is accessed(modified) without manager_mutex.
>> making gcwq->flags be accessed only form gcwq->lock C.S. will help the reviewer.
>>
>> I don't like adding special things/code when not-absolutely-required.
> 
> I really fail to see this.  The flag has to stay stable while
> manage_mutex is held no matter where you test it. 

Only one bit is stable, the whole flags can be changed outside.

I prefer the whole byte or short or int or long is protected under the same synchronization.
I don't prefer different bit uses different synchronization.

> It doesn't make any
> it any more readable whether you test it inside gcwq->lock with the
> comment saying "this won't change while manager_mutex is held" or just
> test it while manager_mutex is held.  It is a synchronization oddity
> no matter what and as long as it's well documented, I don't really see
> the point in the change.
> 

When I read "gcwq->flags & GCWQ_DISASSOCIATED" in create_worker, I thought:
WTF, gcwq->flags can be change by other, is it correct?. When I saw the comments claim
it is correct, I have to use about 30 mins to check whether it is correct in several
places of code in workqueue.c(include check does flags has internal state in all gcwq->lock).
I'm not good on it, but I think there are some reviewers will be confused like me.

Thanks,
Lai
will be 


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