[PATCH net v4] batman-adv: Fix double-hold of meshif when getting enabled

[PATCH net v4] batman-adv: Fix double-hold of meshif when getting enabled

[Sven Eckelmann]

It was originally meant to replace the dev_hold with netdev_hold. But this
was missed in batadv_hardif_enable_interface(). As result, there was an
imbalance and a hang when trying to remove the mesh-interface with
(previously) active hard-interfaces:

  unregister_netdevice: waiting for batadv0 to become free. Usage count = 3

Fixes: 00b35530811f ("batman-adv: adopt netdev_hold() / netdev_put()")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
---
This patch is skipping Simon's normal PR submission to get this problem
fixed faster in Linus' tree. This currently creates quite a lot of wrong
bisect results for syzkaller and it would be better to have this fixed
sooner than later.
---
Changes in v4:
- added Suggested-by: Eric Dumazet <edumazet@google.com>
- added Reported-by: of various syzkaller reports which were affected (during
  bisecting) by this problem
- resubmission after 24h cooldown time
- added kernel message during hang to commit message
- Link to v3: https://lore.kernel.org/r/20250409073524.557189-1-sven@narfation.org
Changes in v3:
- fix submitter address
- Link to v2: https://lore.kernel.org/r/20250409073304.556841-1-sw@simonwunderlich.de
Changes in v2:
- add missing commit message
- Link to v1: https://lore.kernel.org/r/20250409073000.556263-1-sven@narfation.org
---
 net/batman-adv/hard-interface.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/net/batman-adv/hard-interface.c b/net/batman-adv/hard-interface.c
index f145f96626531053bbf8f58a31f28f625a9d80f9..7cd4bdcee43935b9e5fb7d1696430909b7af67b4 100644
--- a/net/batman-adv/hard-interface.c
+++ b/net/batman-adv/hard-interface.c
@@ -725,7 +725,6 @@ int batadv_hardif_enable_interface(struct batadv_hard_iface *hard_iface,
 
 	kref_get(&hard_iface->refcount);
 
-	dev_hold(mesh_iface);
 	netdev_hold(mesh_iface, &hard_iface->meshif_dev_tracker, GFP_ATOMIC);
 	hard_iface->mesh_iface = mesh_iface;
 	bat_priv = netdev_priv(hard_iface->mesh_iface);

---
base-commit: 61f96e684edd28ca40555ec49ea1555df31ba619
change-id: 20250410-double_hold_fix-8f0a87f72ad9

Best regards,
-- 
Sven Eckelmann <sven@narfation.org>

Re: [PATCH net v4] batman-adv: Fix double-hold of meshif when getting enabled

[Simon Horman]

On Thu, Apr 10, 2025 at 08:58:51PM +0200, Sven Eckelmann wrote:
> It was originally meant to replace the dev_hold with netdev_hold. But this
> was missed in batadv_hardif_enable_interface(). As result, there was an
> imbalance and a hang when trying to remove the mesh-interface with
> (previously) active hard-interfaces:
> 
>   unregister_netdevice: waiting for batadv0 to become free. Usage count = 3
> 
> Fixes: 00b35530811f ("batman-adv: adopt netdev_hold() / netdev_put()")
> Signed-off-by: Sven Eckelmann <sven@narfation.org>
> ---
> This patch is skipping Simon's normal PR submission to get this problem
> fixed faster in Linus' tree. This currently creates quite a lot of wrong
> bisect results for syzkaller and it would be better to have this fixed
> sooner than later.
> ---
> Changes in v4:
> - added Suggested-by: Eric Dumazet <edumazet@google.com>
> - added Reported-by: of various syzkaller reports which were affected (during
>   bisecting) by this problem

FWIIW, I don't see those tags at the bottom of the commit message.

> - resubmission after 24h cooldown time
> - added kernel message during hang to commit message
> - Link to v3: https://lore.kernel.org/r/20250409073524.557189-1-sven@narfation.org
> Changes in v3:
> - fix submitter address
> - Link to v2: https://lore.kernel.org/r/20250409073304.556841-1-sw@simonwunderlich.de
> Changes in v2:
> - add missing commit message
> - Link to v1: https://lore.kernel.org/r/20250409073000.556263-1-sven@narfation.org

...