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From: Marek Lindner <mareklindner@neomailbox.ch>
Date: Tue, 16 Jun 2015 22:38:20 +0800
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Subject: Re: [B.A.T.M.A.N.] [PATCHv3 maint 5/5] batman-adv: Fix potential
	synchronization issues in mcast tvlv handler
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To: b.a.t.m.a.n@lists.open-mesh.org, Linus =?ISO-8859-1?Q?L=FCssing?= <linus.luessing@c0d3.blue>


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On Tuesday, June 16, 2015 22:12:00 Marek Lindner wrote:
> On Tuesday, June 16, 2015 15:17:23 Linus L=FCssing wrote:
> > +               /* flag checks above + mcast_handler_lock prevents =
this */
> > +               if (unlikely(!hlist_unhashed(node)))
> > +                       BUG();
> > +
>=20
> I don't think this will work because hlist_unhashed() checks for node=
=2D>pprev
> being NULL or not. hlist_del_rcu() sets node->pprev to LIST_POISON2.
>=20
> We could also use BUG_ON() for readability. Something like:
>=20
> BUG_ON(node->pprev =3D=3D LIST_POISON2);
>=20
> Though there are not many code sections working with LIST_POISON2 out=
side
> the list handling code.

Correction: Sven pointed out that we should not depend on LIST_POISON2 =
as it=20
may point to some valid code or something utterly random depending on k=
ernel=20
configs.

I had overlooked that you had switched to hlist_del_init_rcu() already =
which=20
makes your check valid. Still, would you consider using BUG_ON() ?

Cheers,
Marek

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