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From: Lai Jiangshan <laijs@cn.fujitsu.com>
To: Tejun Heo <tj@kernel.org>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH 05/11 V5] workqueue: Add @bind arguement back without change any thing
Date: Fri, 07 Sep 2012 10:11:56 +0800	[thread overview]
Message-ID: <504957EC.60305@cn.fujitsu.com> (raw)
In-Reply-To: <20120906165145.GE29092@google.com>

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 



  reply	other threads:[~2012-09-07  2:10 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-09-05 10:37 [PATCH 00/11 V5] workqueue: reimplement unbind/rebind Lai Jiangshan
2012-09-05 10:37 ` [PATCH 01/11 V5] workqueue: ensure the wq_worker_sleeping() see the right flags Lai Jiangshan
2012-09-05 10:37 ` [PATCH 02/11 V5] workqueue: async idle rebinding Lai Jiangshan
2012-09-05 18:06   ` Tejun Heo
2012-09-06  1:28     ` Lai Jiangshan
2012-09-05 10:37 ` [PATCH 03/11 V5] workqueue: new day don't need WORKER_REBIND for busy rebinding Lai Jiangshan
2012-09-05 18:31   ` Tejun Heo
2012-09-06  2:10     ` Lai Jiangshan
2012-09-05 10:37 ` [PATCH 04/11 V5] workqueue: remove WORKER_REBIND Lai Jiangshan
2012-09-05 10:37 ` [PATCH 05/11 V5] workqueue: Add @bind arguement back without change any thing Lai Jiangshan
2012-09-05 19:49   ` Tejun Heo
2012-09-06  1:04     ` Lai Jiangshan
2012-09-06 16:51       ` Tejun Heo
2012-09-07  2:11         ` Lai Jiangshan [this message]
2012-09-07 19:37           ` Tejun Heo
2012-09-05 10:37 ` [PATCH 06/11 V5] workqueue: unbind manager Lai Jiangshan
2012-09-05 10:37 ` [PATCH 07/11 V5] workqueue: rebind manager Lai Jiangshan
2012-09-05 10:37 ` [PATCH 08/11 V5] workqueue: unbind newly created worker Lai Jiangshan
2012-09-05 10:37 ` [PATCH 09/11 V5] workqueue: rebind " Lai Jiangshan
2012-09-05 16:19   ` Lai Jiangshan
2012-09-05 10:37 ` [PATCH 10/11 V5] workqueue: unbind/rebind without manager_mutex Lai Jiangshan
2012-09-05 20:04   ` Tejun Heo
2012-09-06 10:44     ` Lai Jiangshan
2012-09-06 17:00       ` Tejun Heo
2012-09-05 10:37 ` [PATCH 11/11 V5] workqueue: remove manager_mutex Lai Jiangshan

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