linux-kernel - Re: [PATCH] module: add kset_obj

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Message-ID: <20130410172713.GB1881@kroah.com>
Date:	Wed, 10 Apr 2013 10:27:13 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Veaceslav Falico <vfalico@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	rusty@...tcorp.com.au, bhelgaas@...gle.com
Subject: Re: [PATCH] module: add kset_obj_exists() and use it

On Tue, Apr 09, 2013 at 01:22:09PM +0200, Veaceslav Falico wrote:
> Add a new function, kset_obj_exists(), which is identical to
> kset_find_obj() but doesn't take a reference to the kobject
> found and only returns bool if found/not found.
> 
> The main purpose would be to avoid the possible race scenario,
> when we could get the reference in between the kref_put() and
> kobject_release() functions (i.e. kref_put() already ran,
> refcount became 0, but the kobject_release() function still
> didn't run, and we try to get via kobject_get() and thus ending
> up with a released kobject). It can be triggered, for example,
> by running insmod/rmmod bonding in parallel, which ends up in
> a race between kset_obj_find() in mod_sysfs_init() and rmmod's
> mod_sysfs_fini()/kobject_put().

As Rusty points out, this isn't a kobject issue that can be solved with
a new api call, but rather, the user of the kobject code needs to be
fixed, with something like his proposed patch instead.

So, because of this, I can't take this patch, sorry.

greg k-h
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