From patchwork Sat Mar 5 12:28:26 2011 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sven Eckelmann X-Patchwork-Id: 877 Return-Path: Received: from v3-1039.vlinux.de (narfation.org [79.140.41.39]) by open-mesh.org (Postfix) with ESMTPS id 749C71542B3 for ; Sat, 5 Mar 2011 13:29:50 +0100 (CET) Authentication-Results: open-mesh.org; dkim=pass (1024-bit key) header.i=@narfation.org; dkim-adsp=pass Received: from sven-desktop.home.narfation.org (i59F6B254.versanet.de [89.246.178.84]) by v3-1039.vlinux.de (Postfix) with ESMTPSA id 0C5659405E; Sat, 5 Mar 2011 13:29:51 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=narfation.org; s=mail; t=1299328192; bh=cb7rSNb7fP9l3SlLEHdi6Pr7lsP0VW4qyu6WMYSXzUo=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References; b=Dnwz2EjwHZp8H+Id9Slm1Pq8kej/+MArt0HDM2xa8LGhe+H6Cy+HiTe0n6T9oSUep 9jrIGojq/77SSIBQJGzOcXw2bVQnJWj+uAcGOW+0N/8+3WgOFas+h07Qkfhk5F200x RdoCZnhM7anOYoneB8NIYS9iK1tZcwPH7CDxKUmo= From: Sven Eckelmann To: davem@davemloft.net Date: Sat, 5 Mar 2011 13:28:26 +0100 Message-Id: <1299328122-21468-13-git-send-email-sven@narfation.org> X-Mailer: git-send-email 1.7.2.3 In-Reply-To: <1299328122-21468-1-git-send-email-sven@narfation.org> References: <1299328122-21468-1-git-send-email-sven@narfation.org> Cc: netdev@vger.kernel.org, b.a.t.m.a.n@lists.open-mesh.org, Marek Lindner Subject: [B.A.T.M.A.N.] [PATCH 12/28] batman-adv: Correct rcu refcounting for gw_node X-BeenThere: b.a.t.m.a.n@lists.open-mesh.org X-Mailman-Version: 2.1.13 Precedence: list Reply-To: The list for a Better Approach To Mobile Ad-hoc Networking List-Id: The list for a Better Approach To Mobile Ad-hoc Networking List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 05 Mar 2011 12:29:50 -0000 From: Marek Lindner It might be possible that 2 threads access the same data in the same rcu grace period. The first thread calls call_rcu() to decrement the refcount and free the data while the second thread increases the refcount to use the data. To avoid this race condition all refcount operations have to be atomic. Reported-by: Sven Eckelmann Signed-off-by: Marek Lindner --- net/batman-adv/gateway_client.c | 37 ++++++++++++++++--------------------- net/batman-adv/types.h | 2 +- 2 files changed, 17 insertions(+), 22 deletions(-) diff --git a/net/batman-adv/gateway_client.c b/net/batman-adv/gateway_client.c index 429a013..517e001 100644 --- a/net/batman-adv/gateway_client.c +++ b/net/batman-adv/gateway_client.c @@ -28,20 +28,18 @@ #include #include -static void gw_node_free_ref(struct kref *refcount) +static void gw_node_free_rcu(struct rcu_head *rcu) { struct gw_node *gw_node; - gw_node = container_of(refcount, struct gw_node, refcount); + gw_node = container_of(rcu, struct gw_node, rcu); kfree(gw_node); } -static void gw_node_free_rcu(struct rcu_head *rcu) +static void gw_node_free_ref(struct gw_node *gw_node) { - struct gw_node *gw_node; - - gw_node = container_of(rcu, struct gw_node, rcu); - kref_put(&gw_node->refcount, gw_node_free_ref); + if (atomic_dec_and_test(&gw_node->refcount)) + call_rcu(&gw_node->rcu, gw_node_free_rcu); } void *gw_get_selected(struct bat_priv *bat_priv) @@ -61,25 +59,26 @@ void gw_deselect(struct bat_priv *bat_priv) bat_priv->curr_gw = NULL; if (gw_node) - kref_put(&gw_node->refcount, gw_node_free_ref); + gw_node_free_ref(gw_node); } -static struct gw_node *gw_select(struct bat_priv *bat_priv, - struct gw_node *new_gw_node) +static void gw_select(struct bat_priv *bat_priv, struct gw_node *new_gw_node) { struct gw_node *curr_gw_node = bat_priv->curr_gw; - if (new_gw_node) - kref_get(&new_gw_node->refcount); + if (new_gw_node && !atomic_inc_not_zero(&new_gw_node->refcount)) + new_gw_node = NULL; bat_priv->curr_gw = new_gw_node; - return curr_gw_node; + + if (curr_gw_node) + gw_node_free_ref(curr_gw_node); } void gw_election(struct bat_priv *bat_priv) { struct hlist_node *node; - struct gw_node *gw_node, *curr_gw_tmp = NULL, *old_gw_node = NULL; + struct gw_node *gw_node, *curr_gw_tmp = NULL; uint8_t max_tq = 0; uint32_t max_gw_factor = 0, tmp_gw_factor = 0; int down, up; @@ -174,14 +173,10 @@ void gw_election(struct bat_priv *bat_priv) curr_gw_tmp->orig_node->gw_flags, curr_gw_tmp->orig_node->router->tq_avg); - old_gw_node = gw_select(bat_priv, curr_gw_tmp); + gw_select(bat_priv, curr_gw_tmp); } rcu_read_unlock(); - - /* the kfree() has to be outside of the rcu lock */ - if (old_gw_node) - kref_put(&old_gw_node->refcount, gw_node_free_ref); } void gw_check_election(struct bat_priv *bat_priv, struct orig_node *orig_node) @@ -242,7 +237,7 @@ static void gw_node_add(struct bat_priv *bat_priv, memset(gw_node, 0, sizeof(struct gw_node)); INIT_HLIST_NODE(&gw_node->list); gw_node->orig_node = orig_node; - kref_init(&gw_node->refcount); + atomic_set(&gw_node->refcount, 1); spin_lock_bh(&bat_priv->gw_list_lock); hlist_add_head_rcu(&gw_node->list, &bat_priv->gw_list); @@ -325,7 +320,7 @@ void gw_node_purge(struct bat_priv *bat_priv) gw_deselect(bat_priv); hlist_del_rcu(&gw_node->list); - call_rcu(&gw_node->rcu, gw_node_free_rcu); + gw_node_free_ref(gw_node); } diff --git a/net/batman-adv/types.h b/net/batman-adv/types.h index 084604a..cfbeb45 100644 --- a/net/batman-adv/types.h +++ b/net/batman-adv/types.h @@ -98,7 +98,7 @@ struct gw_node { struct hlist_node list; struct orig_node *orig_node; unsigned long deleted; - struct kref refcount; + atomic_t refcount; struct rcu_head rcu; };