linux-kernel - Re: [RFC PATCH 2/2] drivers/base: add managed token devres interfaces

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Date:	Thu, 17 Apr 2014 14:50:39 -0600
From:	Shuah Khan <shuah.kh@...sung.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	gregkh@...uxfoundation.org, m.chehab@...sung.com,
	rafael.j.wysocki@...el.com, linux@...ck-us.net, toshi.kani@...com,
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
	shuahkhan@...il.com
Subject: Re: [RFC PATCH 2/2] drivers/base: add managed token devres interfaces

On 04/17/2014 02:10 PM, Tejun Heo wrote:
> On Thu, Apr 17, 2014 at 02:01:32PM -0600, Shuah Khan wrote:
>> Operating on the lock should be atomic, which is what devres_update()
>> is doing. It can be simplified as follows by holding devres_lock
>> in devm_token_lock().
>>
>> spin_lock_irqsave(&dev->devres_lock, flags);
>> if (tkn_ptr->status == TOKEN_DEVRES_FREE)
>> 	tkn_ptr->status = TOKEN_DEVRES_BUSY;
>> spin_unlock_irqrestore(&dev->devres_lock, flags);
>>
>> Is this in-line with what you have in mind?
>
> How is that different from tkn_ptr->status = TOKEN_DEVRES_BUSY?
>

I see what you are saying. The code path doesn't ensure two threads
not getting the lock. I have a bug in here that my rc settings aren't
protected. You probably noticed that the RFC tag on the patch and this
isn't fully cooked yet.

I started working on driver changes that use this token and I might have
to add owner for the token as well. I hope to work these details out and
send a real patch.

thanks,
-- Shuah

-- 
Shuah Khan
Senior Linux Kernel Developer - Open Source Group
Samsung Research America(Silicon Valley)
shuah.kh@...sung.com | (970) 672-0658
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