[PATCH 6.18 220/333] batman-adv: Avoid double-rtnl_lock ELP metric worker

Greg Kroah-Hartman
2026-03-17T17:20:48Z

From: Sven Eckelmann <sven@narfation.org>

commit cfc83a3c71517b59c1047db57da31e26a9dc2f33 upstream.

batadv_v_elp_get_throughput() might be called when the RTNL lock is already
held. This could be problematic when the work queue item is cancelled via
cancel_delayed_work_sync() in batadv_v_elp_iface_disable(). In this case,
an rtnl_lock() would cause a deadlock.

To avoid this, rtnl_trylock() was used in this function to skip the
retrieval of the ethtool information in case the RTNL lock was already
held.

But for cfg80211 interfaces, batadv_get_real_netdev() was called - which
also uses rtnl_lock(). The approach for __ethtool_get_link_ksettings() must
also be used instead and the lockless version __batadv_get_real_netdev()
has to be called.

Cc: stable@vger.kernel.org
Fixes: 8c8ecc98f5c6 ("batman-adv: Drop unmanaged ELP metric worker")
Reported-by: Christian Schmidbauer <github@grische.xyz>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Tested-by: Sören Skaarup <freifunk_nordm4nn@gmx.de>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/batman-adv/bat_v_elp.c | 10 +++++++++-
net/batman-adv/hard-interface.c | 8 ++++----
net/batman-adv/hard-interface.h | 1 +
3 files changed, 14 insertions(+), 5 deletions(-)

--- a/net/batman-adv/bat_v_elp.c
+++ b/net/batman-adv/bat_v_elp.c
@@ -111,7 +111,15 @@ static bool batadv_v_elp_get_throughput(
/* unsupported WiFi driver version */
goto default_throughput;

- real_netdev = batadv_get_real_netdev(hard_iface->net_dev);
+ /* only use rtnl_trylock because the elp worker will be cancelled while
+ * the rntl_lock is held. the cancel_delayed_work_sync() would otherwise
+ * wait forever when the elp work_item was started and it is then also
+ * trying to rtnl_lock
+ */
+ if (!rtnl_trylock())
+ return false;
+ real_netdev = __batadv_get_real_netdev(hard_iface->net_dev);
+ rtnl_unlock();
if (!real_netdev)
goto default_throughput;

--- a/net/batman-adv/hard-interface.c
+++ b/net/batman-adv/hard-interface.c
@@ -204,7 +204,7 @@ static bool batadv_is_valid_iface(const
}

/**
- * batadv_get_real_netdevice() - check if the given netdev struct is a virtual
+ * __batadv_get_real_netdev() - check if the given netdev struct is a virtual
* interface on top of another 'real' interface
* @netdev: the device to check
*
@@ -214,7 +214,7 @@ static bool batadv_is_valid_iface(const
* Return: the 'real' net device or the original net device and NULL in case
* of an error.
*/
-static struct net_device *batadv_get_real_netdevice(struct net_device *netdev)
+struct net_device *__batadv_get_real_netdev(struct net_device *netdev)
{
struct batadv_hard_iface *hard_iface = NULL;
struct net_device *real_netdev = NULL;
@@ -267,7 +267,7 @@ struct net_device *batadv_get_real_netde
struct net_device *real_netdev;

rtnl_lock();
- real_netdev = batadv_get_real_netdevice(net_device);
+ real_netdev = __batadv_get_real_netdev(net_device);
rtnl_unlock();

return real_netdev;
@@ -336,7 +336,7 @@ static u32 batadv_wifi_flags_evaluate(st
if (batadv_is_cfg80211_netdev(net_device))
wifi_flags |= BATADV_HARDIF_WIFI_CFG80211_DIRECT;

- real_netdev = batadv_get_real_netdevice(net_device);
+ real_netdev = __batadv_get_real_netdev(net_device);
if (!real_netdev)
return wifi_flags;

--- a/net/batman-adv/hard-interface.h
+++ b/net/batman-adv/hard-interface.h
@@ -67,6 +67,7 @@ enum batadv_hard_if_bcast {

extern struct notifier_block batadv_hard_if_notifier;

+struct net_device *__batadv_get_real_netdev(struct net_device *net_device);
struct net_device *batadv_get_real_netdev(struct net_device *net_device);
bool batadv_is_cfg80211_hardif(struct batadv_hard_iface *hard_iface);
bool batadv_is_wifi_hardif(struct batadv_hard_iface *hard_iface);