netdev - Re: [B.A.T.M.A.N.] batman-adv: gpf in batadv_slide_own_bcast

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Date:	Tue, 26 Feb 2013 13:52:46 +0800
From:	Marek Lindner <lindner_marek@...oo.de>
To:	b.a.t.m.a.n@...ts.open-mesh.org
Cc:	Sasha Levin <sasha.levin@...cle.com>,
	Antonio Quartulli <ordex@...istici.org>,
	netdev@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Simon Wunderlich <siwu@....tu-chemnitz.de>,
	Dave Jones <davej@...hat.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [B.A.T.M.A.N.] batman-adv: gpf in batadv_slide_own_bcast_window

On Saturday, February 23, 2013 02:37:06 Sasha Levin wrote:
> I'm confused about how batadv_orig_hash_del_if removes an interface from
> the hashtable. I see the hashtable is using rcu to protect it, but when we
> delete an entry we free it straight away by calling
> batadv_orig_node_del_if() and not going through kfree_rcu().
> 
> Is there a reason behind doing that, or might it be the cause of the
> problem we're seeing here?

Maybe I am overlooking something but it seems to me access to this memory is 
protected by the same lock: orig_node->ogm_cnt_lock
Before batadv_orig_node_del_if() is called this lock is acquired and 
batadv_slide_own_bcast_window() also attempts acquire the orig_node-
>ogm_cnt_lock spinlock before writing to this chunk of memory.

Do we know for certain that batadv_orig_hash_del_if() is involved or is that a 
guess at this point ? If you ask me the next for-loop in 
batadv_orig_hash_del_if() looks more suspicious than the first one. The 
interfaces get renumbered without any protection. Could be a regression from 
the orig_hash_lock removal (the comments refer to a now inexisting lock).

Cheers,
Marek
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