linux-kernel - Re: kobject_init_and

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Message-ID: <20200603002205.GE6578@ziepe.ca>
Date:   Tue, 2 Jun 2020 21:22:05 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     James Bottomley <James.Bottomley@...senPartnership.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Wang Hai <wanghai38@...wei.com>, cl@...ux.com,
        penberg@...nel.org, rientjes@...gle.com, iamjoonsoo.kim@....com,
        akpm@...ux-foundation.org, khlebnikov@...dex-team.ru,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: kobject_init_and_add is easy to misuse

On Tue, Jun 02, 2020 at 02:51:10PM -0700, James Bottomley wrote:

> My first thought was "what?  I got suckered into creating a patch",
> thanks ;-)  But now I look, all the error paths do unwind back to the
> initial state, so kfree() on error looks to be completely correct. 

It doesn't fully unwind if the kobject is put into a kset, then
another thread can get the kref during kset_find_obj() and kfree() won't
wait for the kref to go to 0. It must use put.

Jason