linux-kernel - Re: [PATCH 1/2] kref: add kref_test_and

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Date:	Wed, 05 Jan 2011 14:35:04 +0100
From:	Jerome Marchand <jmarchan@...hat.com>
To:	Greg KH <greg@...ah.com>
CC:	Vivek Goyal <vgoyal@...hat.com>, Jens Axboe <jaxboe@...ionio.com>,
	Satoru Takeuchi <takeuchi_satoru@...fujitsu.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] kref: add kref_test_and_get

On 01/04/2011 09:57 PM, Greg KH wrote:
> On Tue, Jan 04, 2011 at 04:52:26PM +0100, Jerome Marchand wrote:
>>
>> Add kref_test_and_get() function, which atomically add a reference only if
>> refcount is not zero. This prevent to add a reference to an object that is
>> already being removed.
> 
> We just removed a function like this recently as it really isn't the
> solution for what you need here at all.

What function are you talking about? kref_set? If yes, I don't see the
similarity between this function and mine.

Regards
Jerome

> 
> Please use a lock that protects the desctruction of the kref, like the
> rest of the kernel, to keep someone from grabing a reference while the
> device could be going away.  That's the only way to safely do this.
> 
> See the archives for why this overall, isn't a good idea for a kref to
> have this type of function.
> 
> thanks,
> 
> greg k-h

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