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From: "Linus Lüssing" <linus.luessing@web.de>
To: The list for a Better Approach To Mobile Ad-hoc Networking
	<b.a.t.m.a.n@lists.open-mesh.org>
Subject: Re: [B.A.T.M.A.N.] [PATCH 2/7] batman-adv: Correct rcu refcounting for softif_neigh
Date: Thu, 10 Feb 2011 13:45:44 +0100	[thread overview]
Message-ID: <20110210124544.GC13038@Sellars> (raw)
In-Reply-To: <1296832896-30081-3-git-send-email-linus.luessing@ascom.ch>

On Fri, Feb 04, 2011 at 04:21:31PM +0100, Linus Lüssing wrote:
> @@ -143,8 +140,11 @@ static struct softif_neigh *softif_neigh_get(struct bat_priv *bat_priv,
>  		if (softif_neigh->vid != vid)
>  			continue;
>  
> +		if (!atomic_inc_not_zero(&softif_neigh->refcount))
> +			continue;
> +
>  		softif_neigh->last_seen = jiffies;
> -		goto found;
> +		goto out;
>  	}
Hmm, we could do a rcu_read_unlock() here, already, I think. Would
it be better to do so, keeping the rcu grace period as small as
possible?
>  
>  	softif_neigh = kzalloc(sizeof(struct softif_neigh), GFP_ATOMIC);
> @@ -154,15 +154,14 @@ static struct softif_neigh *softif_neigh_get(struct bat_priv *bat_priv,
>  	memcpy(softif_neigh->addr, addr, ETH_ALEN);
>  	softif_neigh->vid = vid;
>  	softif_neigh->last_seen = jiffies;
> -	kref_init(&softif_neigh->refcount);
> +	/* initialize with 2 - caller decrements counter by one */
> +	atomic_set(&softif_neigh->refcount, 2);
>  
>  	INIT_HLIST_NODE(&softif_neigh->list);
>  	spin_lock_bh(&bat_priv->softif_neigh_lock);
>  	hlist_add_head_rcu(&softif_neigh->list, &bat_priv->softif_neigh_list);
>  	spin_unlock_bh(&bat_priv->softif_neigh_lock);
>  
> -found:
> -	kref_get(&softif_neigh->refcount);
>  out:
>  	rcu_read_unlock();
>  	return softif_neigh;

The rest of the new atomic handling seems fine. Just two more
things I noticed while reading the softif_neigh specific code:
bat_priv->softif_neigh needs to be changed to a rcu-protected
pointer.

There's a race condition in softif_neigh_seq_print_text(), between
the rcu_read_unlock() and rcu_read_lock() the number of
softif_neigh's can have increased and there's no check for
accidentally writing outside of the allocated buffer.

Cheers, Linus

  reply	other threads:[~2011-02-10 12:45 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-01-30  1:52 [B.A.T.M.A.N.] Reordered rcu refcounting Sven Eckelmann
2011-01-30  1:52 ` [B.A.T.M.A.N.] [PATCH 1/4] batman-adv: Correct rcu refcounting for gw_node Sven Eckelmann
2011-02-02 17:37   ` [B.A.T.M.A.N.] [PATCH] " Linus Lüssing
2011-02-02 19:49     ` Marek Lindner
2011-02-02 20:43       ` Linus Lüssing
2011-02-02 21:42     ` Sven Eckelmann
2011-02-03  0:19       ` Marek Lindner
2011-02-03  9:55       ` Linus Lüssing
2011-02-03 10:01         ` Sven Eckelmann
2011-02-03 14:43     ` [B.A.T.M.A.N.] [PATCH 1/3] " Linus Lüssing
2011-02-03 17:56       ` Sven Eckelmann
2011-02-03 14:43     ` [B.A.T.M.A.N.] [PATCH 2/3] batman-adv: add __rcu annotations " Linus Lüssing
2011-02-03 14:43     ` [B.A.T.M.A.N.] [PATCH 3/3] batman-adv: Increase orig_node refcount before releasing rcu read lock Linus Lüssing
2011-01-30  1:52 ` [B.A.T.M.A.N.] [PATCH 2/4] batman-adv: Correct rcu refcounting for softif_neigh Sven Eckelmann
2011-01-30  1:52 ` [B.A.T.M.A.N.] [PATCH 3/4] batman-adv: Correct rcu refcounting for batman_if Sven Eckelmann
2011-01-30  1:52 ` [B.A.T.M.A.N.] [PATCH 4/4] batman-adv: Correct rcu refcounting for neigh_node Sven Eckelmann
2011-01-30 15:20   ` [B.A.T.M.A.N.] [PATCHv2 " Sven Eckelmann
2011-02-03 17:02 ` [B.A.T.M.A.N.] Reordered rcu refcounting Marek Lindner
2011-02-03 17:03   ` [B.A.T.M.A.N.] [PATCH 1/4] batman-adv: Correct rcu refcounting for gw_node Marek Lindner
2011-02-03 17:03   ` [B.A.T.M.A.N.] [PATCH 2/4] batman-adv: Correct rcu refcounting for softif_neigh Marek Lindner
2011-02-03 17:03   ` [B.A.T.M.A.N.] [PATCH 3/4] batman-adv: Correct rcu refcounting for batman_if Marek Lindner
2011-02-03 17:03   ` [B.A.T.M.A.N.] [PATCH 4/4] batman-adv: Correct rcu refcounting for neigh_node Marek Lindner
2011-02-04 12:59     ` [B.A.T.M.A.N.] [PATCHv2 " Marek Lindner
2011-02-04 15:21   ` [B.A.T.M.A.N.] Reordered rcu refcounting, v3 Linus Lüssing
2011-02-04 15:21   ` [B.A.T.M.A.N.] [PATCH 1/7] batman-adv: Correct rcu refcounting for gw_node Linus Lüssing
2011-02-10 11:01     ` Linus Lüssing
2011-02-04 15:21   ` [B.A.T.M.A.N.] [PATCH 2/7] batman-adv: Correct rcu refcounting for softif_neigh Linus Lüssing
2011-02-10 12:45     ` Linus Lüssing [this message]
2011-02-10 13:57       ` Marek Lindner
2011-02-12 21:23         ` Linus Lüssing
2011-02-04 15:21   ` [B.A.T.M.A.N.] [PATCH 3/7] batman-adv: Correct rcu refcounting for batman_if Linus Lüssing
2011-02-04 15:21   ` [B.A.T.M.A.N.] [PATCH 4/7] batman-adv: Correct rcu refcounting for neigh_node Linus Lüssing
2011-02-04 15:21   ` [B.A.T.M.A.N.] [PATCH 5/7] batman-adv: Make bat_priv->curr_gw an rcu protected pointer Linus Lüssing
2011-02-08 13:18     ` Marek Lindner
2011-02-10 10:42       ` Linus Lüssing
2011-02-10 14:25         ` Marek Lindner
2011-02-12 21:21           ` Linus Lüssing
2011-02-12 21:21           ` [B.A.T.M.A.N.] [PATCHv2 " Linus Lüssing
2011-02-13 21:09             ` Marek Lindner
2011-02-04 15:21   ` [B.A.T.M.A.N.] [PATCH 6/7] batman-adv: add __rcu annotations for gw_node Linus Lüssing
2011-02-13 21:10     ` Marek Lindner
2011-02-04 15:21   ` [B.A.T.M.A.N.] [PATCH 7/7] batman-adv: Increase orig_node refcount before releasing rcu read lock Linus Lüssing
2011-02-04 16:33     ` [B.A.T.M.A.N.] [PATCHv2 " Linus Lüssing
2011-02-13 21:11     ` [B.A.T.M.A.N.] [PATCH " Marek Lindner

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