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Date: Wed, 14 Oct 2026 13:06:18 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: Nicolai Buchwitz <nb@tipi-net.de>
Cc: "David S. Miller" <davem@davemloft.net>, Eric Dumazet
 <edumazet@kernel.org>, Paolo Abeni <pabeni@redhat.com>, Simon Horman
 <horms@kernel.org>, Oleksij Rempel <o.rempel@pengutronix.de>, Maxime
 Chevallier <maxime.chevallier@bootlin.com>, Andrew Lunn
 <andrew+netdev@lunn.ch>, Maxime Coquelin <mcoquelin.stm32@gmail.com>,
 Alexandre Torgue <alexandre.torgue@foss.st.com>, Jose Abreu
 <Jose.Abreu@synopsys.com>, Saeed Mahameed <saeedm@nvidia.com>, Tariq Toukan
 <tariqt@nvidia.com>, Mark Bloch <mbloch@nvidia.com>, Leon Romanovsky
 <leon@kernel.org>, Dragos Tatulea <dtatulea@nvidia.com>, Alexei Lazar
 <alazar@nvidia.com>, netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
 linux-stm32@st-md-mailman.stormreply.com,
 linux-arm-kernel@lists.infradead.org, linux-rdma@vger.kernel.org
Subject: Re: [PATCH net-next 0/3] net: use skb_share_check() in loopback
 selftest hooks
Message-ID: <20261014130618.4c50f817@kernel.org>
In-Reply-To: <20261007-nb-net-selftest-shared-net-v1-0-458369bfa1ba@tipi-net.de>
References: <20261007-nb-net-selftest-shared-net-v1-0-458369bfa1ba@tipi-net.de>
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On Wed, 07 Oct 2026 20:29:21 +0200 Nicolai Buchwitz wrote:
> The loopback selftest hooks can get a shared skb when another handler
> is bound to the device. Linearizing a non-linear frame then hits
> BUG_ON(skb_shared()) in pskb_expand_head().
> 
> Stumbled over this on RPi CM4 (bcmgenet, with jumbo series applied +
> WIP selftest patches) with a packet socket open at the same time as
> running ethtool -t.
> 
> stmmac and mlx5 seem to have the same pattern, xgbe already handles
> shared skbs. Patches 2 and 3 are compile tested only.
> 
> As the impact is pretty limited and doesn't seem to bother anyone in
> the wild, I've chosen net-next, but kept the Fixes tags. That matches
> what Paolo suggested during the LPC track.

Wonder if we should follow up and rename skb_unshare to skb_unclone_full
or some such? The "share" in the name is quite confusing for people who
haven't been around for 10+ years..