Re: [PATCH] module: add kset_obj_exists() and use it

[Veaceslav Falico]

On Thu, Apr 11, 2013 at 11:28:06AM +0930, Rusty Russell wrote:
> Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> 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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