netdev - Re: [PATCH net-next 1/2] net: vlan: Replace BUG() with WARN_ON_ONCE() in vlan_dev

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Message-ID: <20250611171540.27715f36@kernel.org>
Date: Wed, 11 Jun 2025 17:15:40 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Gal Pressman <gal@...dia.com>
Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Andrew Lunn
 <andrew+netdev@...n.ch>, <netdev@...r.kernel.org>, Alex Lazar
 <alazar@...dia.com>, "Dragos Tatulea" <dtatulea@...dia.com>
Subject: Re: [PATCH net-next 1/2] net: vlan: Replace BUG() with
 WARN_ON_ONCE() in vlan_dev_* stubs

On Tue, 10 Jun 2025 10:26:10 +0300 Gal Pressman wrote:
> This code should not be reached, as callers of these functions should
> always check for is_vlan_dev() first, but the usage of BUG() is not
> recommended, replace it with WARN_ON() instead.

Did you try something along the lines of:

diff --git a/include/linux/if_vlan.h b/include/linux/if_vlan.h
index 38456b42cdb5..f24af2988fd9 100644
--- a/include/linux/if_vlan.h
+++ b/include/linux/if_vlan.h
@@ -81,7 +81,8 @@ extern void vlan_ioctl_set(int (*hook)(struct net *, void __user *));

 static inline bool is_vlan_dev(const struct net_device *dev)
 {
-        return dev->priv_flags & IFF_802_1Q_VLAN;
+        return IS_ENABLED(CONFIG_VLAN_8021Q) &&
+               dev->priv_flags & IFF_802_1Q_VLAN;
 }

 #define skb_vlan_tag_present(__skb)    (!!(__skb)->vlan_all)

This should let the compiler eliminate the dead code completely,
assuming it truly dead. We can still replace the BUG()s as 
a of cleanup but I think the above is strictly preferable as 
a solution to your problem?