[PATCH net v3] net: Lock lower level devices when updating features

[PATCH net v3] net: Lock lower level devices when updating features

[Cosmin Ratiu]

__netdev_update_features() expects the netdevice to be ops-locked, but
it gets called recursively on the lower level netdevices to sync their
features, and nothing locks those.

This commit fixes that, with the assumption that it shouldn't be possible
for both higher-level and lover-level netdevices to require the instance
lock, because that would lead to lock dependency warnings.

Without this, playing with higher level (e.g. vxlan) netdevices on top
of netdevices with instance locking enabled can run into issues:

WARNING: CPU: 59 PID: 206496 at ./include/net/netdev_lock.h:17 netif_napi_add_weight_locked+0x753/0xa60
[...]
Call Trace:
 <TASK>
 mlx5e_open_channel+0xc09/0x3740 [mlx5_core]
 mlx5e_open_channels+0x1f0/0x770 [mlx5_core]
 mlx5e_safe_switch_params+0x1b5/0x2e0 [mlx5_core]
 set_feature_lro+0x1c2/0x330 [mlx5_core]
 mlx5e_handle_feature+0xc8/0x140 [mlx5_core]
 mlx5e_set_features+0x233/0x2e0 [mlx5_core]
 __netdev_update_features+0x5be/0x1670
 __netdev_update_features+0x71f/0x1670
 dev_ethtool+0x21c5/0x4aa0
 dev_ioctl+0x438/0xae0
 sock_ioctl+0x2ba/0x690
 __x64_sys_ioctl+0xa78/0x1700
 do_syscall_64+0x6d/0x140
 entry_SYSCALL_64_after_hwframe+0x4b/0x53
 </TASK>

Fixes: 7e4d784f5810 ("net: hold netdev instance lock during rtnetlink operations")
Signed-off-by: Cosmin Ratiu <cratiu@nvidia.com>
---
 net/core/dev.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/core/dev.c b/net/core/dev.c
index 1be7cb73a602..521ce3936801 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -10453,6 +10453,7 @@ static void netdev_sync_lower_features(struct net_device *upper,
 		if (!(features & feature) && (lower->features & feature)) {
 			netdev_dbg(upper, "Disabling feature %pNF on lower dev %s.\n",
 				   &feature, lower->name);
+			netdev_lock_ops(lower);
 			lower->wanted_features &= ~feature;
 			__netdev_update_features(lower);
 
@@ -10461,6 +10462,7 @@ static void netdev_sync_lower_features(struct net_device *upper,
 					    &feature, lower->name);
 			else
 				netdev_features_change(lower);
+			netdev_unlock_ops(lower);
 		}
 	}
 }
-- 
2.45.0

Re: [PATCH net v3] net: Lock lower level devices when updating features

[Stanislav Fomichev]

On 05/09, Cosmin Ratiu wrote:
> __netdev_update_features() expects the netdevice to be ops-locked, but
> it gets called recursively on the lower level netdevices to sync their
> features, and nothing locks those.
> 
> This commit fixes that, with the assumption that it shouldn't be possible
> for both higher-level and lover-level netdevices to require the instance
> lock, because that would lead to lock dependency warnings.
> 
> Without this, playing with higher level (e.g. vxlan) netdevices on top
> of netdevices with instance locking enabled can run into issues:
> 
> WARNING: CPU: 59 PID: 206496 at ./include/net/netdev_lock.h:17 netif_napi_add_weight_locked+0x753/0xa60
> [...]
> Call Trace:
>  <TASK>
>  mlx5e_open_channel+0xc09/0x3740 [mlx5_core]
>  mlx5e_open_channels+0x1f0/0x770 [mlx5_core]
>  mlx5e_safe_switch_params+0x1b5/0x2e0 [mlx5_core]
>  set_feature_lro+0x1c2/0x330 [mlx5_core]
>  mlx5e_handle_feature+0xc8/0x140 [mlx5_core]
>  mlx5e_set_features+0x233/0x2e0 [mlx5_core]
>  __netdev_update_features+0x5be/0x1670
>  __netdev_update_features+0x71f/0x1670
>  dev_ethtool+0x21c5/0x4aa0
>  dev_ioctl+0x438/0xae0
>  sock_ioctl+0x2ba/0x690
>  __x64_sys_ioctl+0xa78/0x1700
>  do_syscall_64+0x6d/0x140
>  entry_SYSCALL_64_after_hwframe+0x4b/0x53
>  </TASK>
> 
> Fixes: 7e4d784f5810 ("net: hold netdev instance lock during rtnetlink operations")
> Signed-off-by: Cosmin Ratiu <cratiu@nvidia.com>

Acked-by: Stanislav Fomichev <sdf@fomichev.me>

Re: [PATCH net v3] net: Lock lower level devices when updating features

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Fri, 9 May 2025 10:28:50 +0300 you wrote:
> __netdev_update_features() expects the netdevice to be ops-locked, but
> it gets called recursively on the lower level netdevices to sync their
> features, and nothing locks those.
> 
> This commit fixes that, with the assumption that it shouldn't be possible
> for both higher-level and lover-level netdevices to require the instance
> lock, because that would lead to lock dependency warnings.
> 
> [...]

Here is the summary with links:
  - [net,v3] net: Lock lower level devices when updating features
    https://git.kernel.org/netdev/net/c/af5f54b0ef9e

You are awesome, thank you!
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