linux-kernel - Re: [PATCH 2/2] block: fix accounting bug on cross partition merges

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Message-ID: <20110105155816.GD2072@kroah.com>
Date:	Wed, 5 Jan 2011 07:58:16 -0800
From:	Greg KH <greg@...ah.com>
To:	Jens Axboe <jaxboe@...ionio.com>
Cc:	Jerome Marchand <jmarchan@...hat.com>,
	Vivek Goyal <vgoyal@...hat.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 2/2] block: fix accounting bug on cross partition merges

On Wed, Jan 05, 2011 at 02:55:51PM +0100, Jens Axboe wrote:
> On 2011-01-04 22:00, Greg KH wrote:
> > On Tue, Jan 04, 2011 at 04:55:13PM +0100, Jerome Marchand wrote:
> >> Also add a refcount to struct hd_struct to keep the partition in
> >> memory as long as users exist. We use kref_test_and_get() to ensure
> >> we don't add a reference to a partition which is going away.
> > 
> > No, don't do this, use a kref correctly and no such function should be
> > needed.
> > 
> >> +	} else {
> >> +		part = disk_map_sector_rcu(rq->rq_disk, blk_rq_pos(rq));
> > 
> > That is the function that should properly increment the reference count
> > on the object.  If the object is "being removed", then it will return
> > NULL and you need to check that.  Do that and you do not need to add:
> 
> It doesn't matter if you do it in there of after the fact, since the
> "lock" (RCU) is being held across the call. See my original suggestion
> here:
> 
> https://lkml.org/lkml/2010/12/17/275

Ok, that's fine, just do it without adding that kref function and I have
no objection :)

thanks,

greg k-h
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