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

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Date:	Thu, 11 Apr 2013 07:05:43 +0200
From:	Veaceslav Falico <vfalico@...hat.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Greg KH <gregkh@...uxfoundation.org>, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, bhelgaas@...gle.com
Subject: Re: [PATCH] module: add kset_obj_exists() and use it

On Thu, Apr 11, 2013 at 11:28:06AM +0930, Rusty Russell wrote:
>Greg KH <gregkh@...uxfoundation.org> writes:
>
>> 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, I'm shocked!  Surely you've been doing this long enough to know
>that we don't use that kind of language on lkml?
>
>To restore the list's reputation as a hostile pressure cooker powered by
>the smouldering remains of flame-roasted newcomers, allow me to correct
>your reply:
>
>        "NAK.  And you smell."

Got it :). Thank you for your input and your patch, I'll come back with a
proper fix when I'll have one.

Thanks all.

>
>Crisis averted,
>Rusty.
>PS.  Thanks :)
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