From mboxrd@z Thu Jan  1 00:00:00 1970
From: Boaz Harrosh <bharrosh@panasas.com>
Subject: Re: [PATCH 8/19]: SCST SYSFS interface implementation
Date: Thu, 11 Nov 2010 16:05:43 +0200
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References: <4CC1CA4D.1090609@vlnb.net> <20101022175624.GA13640@kroah.com> <4CC1DAA2.7030602@vlnb.net> <20101022185437.GA9103@kroah.com> <4CD8566D.1020202@vlnb.net> <20101109002829.GA22633@kroah.com> <4CD9A9B8.70708@vlnb.net> <4CDA6CD4.3010308@panasas.com> <4CDAFE6E.7050200@vlnb.net> <4CDBBE80.40908@panasas.com> <20101111120453.GA672@kroah.com>
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To: Greg KH <greg@kroah.com>
Cc: Vladislav Bolkhovitin <vst@vlnb.net>, linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, scst-devel <scst-devel@lists.sourceforge.net>, James Bottomley <James.Bottomley@HansenPartnership.com>, Andrew Morton <akpm@linux-foundation.org>, FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>, Mike Christie <michaelc@cs.wisc.edu>, Vu Pham <vuhuong@mellanox.com>, Bart Van Assche <bart.vanassche@gmail.com>, James Smart <James.Smart@Emulex.Com>, Joe Eykholt <jeykholt@cisco.com>, Andy Yan <ayan@marvell.com>, Chetan Loke <generationgnu@yahoo.com>, Dmitry Torokhov <dmitry.torokhov@gmail.com>, Hannes Reinecke <hare@suse.de>, Richard Sharpe <realrichardsharpe@gmail.com>, Daniel Henrique Debonzi <debonzi@linux.vnet.ibm.com>

On 11/11/2010 02:04 PM, Greg KH wrote:
> On Thu, Nov 11, 2010 at 11:59:28AM +0200, Boaz Harrosh wrote:
>> 4. Exactly Like 3 but without the extra kref member
>>    Only x_put() changes and x_kref_release() now receives
>>    an x_object
>>
>> int x_put(struct object_x *x)
>> {
>> 	if (kobject_put(&x->kobj) == 1)
>> 		// Like above [3] x_kref_release()
>> 		x_kref_release(x);
>> }
> 
> This is racy, please never do this.
> 

The last ref belongs to the core code. 1 means there are no
more external clients on the object. So it can not race with
decrements. But I guess there is a possibility that it can
race with new increments. If it is the case that new increments
can only come from, say, sysfs access, then if we call the
x_put() == 1 after we are unregistered from sysfs and no new
users are allowed then the counter can only go down and we
have the last reference. No?

Like I said option 4 is delicate it must be done carefully.

> thanks,
> 
> greg k-h

Thanks
Boaz