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Date: Wed, 05 Jan 2011 14:35:04 +0100
From: Jerome Marchand <jmarchan@redhat.com>
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To: Greg KH <greg@kroah.com>
CC: Vivek Goyal <vgoyal@redhat.com>, Jens Axboe <jaxboe@fusionio.com>,
        Satoru Takeuchi <takeuchi_satoru@jp.fujitsu.com>,
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        Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>,
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Subject: Re: [PATCH 1/2] kref: add kref_test_and_get
References: <4D025154.8030400@redhat.com> <20101210165553.GE31737@redhat.com> <4D07D2AC.6000500@fusionio.com> <4D0B68AF.80804@redhat.com> <4D0BB4A1.8080305@fusionio.com> <4D13664C.3020500@redhat.com> <20101223153915.GE9502@redhat.com> <4D13810B.8000304@redhat.com> <20101224192916.GB2082@redhat.com> <4D23423A.60707@redhat.com> <20110104205720.GA4180@kroah.com>
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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