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[34.85.207.234]) by smtp.gmail.com with ESMTPSA id 00721157ae682-84cabe2570fsm14237647b3.38.2026.08.22.13.55.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 22 Aug 2026 13:55:52 -0700 (PDT) Date: Sat, 22 Aug 2026 16:55:52 -0400 From: Willem de Bruijn To: Ilya Maximets , Jakub Kicinski , Ilya Maximets Cc: Norbert Szetei , netdev@vger.kernel.org, "David S. Miller" , Eric Dumazet , Paolo Abeni , Simon Horman , Aaron Conole , Eelco Chaudron , Steffen Klassert , Kuan-Ting Chen , "Michael S. Tsirkin" , linux-kernel@vger.kernel.org, dev@openvswitch.org, Jongmin Jang , Willem de Bruijn Message-ID: In-Reply-To: <86c61c39-901e-489e-aec9-fafe639276e7@ovn.org> References: <34c64d08-0484-4f3b-b61a-ed68115d01a4@ovn.org> <20260821170950.3e278b1f@kernel.org> <86c61c39-901e-489e-aec9-fafe639276e7@ovn.org> Subject: Re: [PATCH net v3 0/3] net: don't strip zerocopy frag markers from a forwarded skb Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Ilya Maximets wrote: > On 8/22/26 2:09 AM, Jakub Kicinski wrote: > > On Fri, 21 Aug 2026 23:45:41 +0200 Ilya Maximets wrote: > >> Unfortunately, this needs a rebase now that a conflicting change > >> for skb_zerocopy() was merged: > > > > Ugh, I was supposed to merge this first, wasn't I? Sorry. > > Not a huge deal, I guess, the conflict is mechanical and the patches > are simple. I can take care of manual backports once we get the > 'failed to apply' emails. Just a bit of busy work. > > > I was hoping for Willem to TAL since skb_tx_error() is a tx ZC > > thing, now I realized that he wasn't CCed :S (please do so on v4) > > FWIW, I CCed a few people on v1 to have a conversation about a proper > fix, but that wasn't fruitful. So, if I were Norbert, I wouldn't > include them for the new versions either as doing so always feels like > me being annoying. :) Having a look now. > For now, the plan is to get v4 of these targeted fixes into net and > stable and then remove skb_tx_error() entirely once net-next is open, > as it seems to have lost all of its prior meaning. The original use case in tun_net_xmit introduced in commit 149d36f7187c ("tun: report orphan frags errors to zero copy callback") still exists. Not sure you can remove the function entirely. The bug is hit when this function is called with a cloned or shared skb. The original zerocopy path through tun_net_xmit was probably expected to not have this problem. Commit 0110d6f22f39 ("tun: orphan an skb on tx") explains why this orphan in tun_net_xmit was needed: a (vhost) zerocopy skb injected in tap1 arriving at tap2 and not being read there indefinitely. Such loops are not allowed for zerocopy. Commit 868eefeb17d4 ("tun: orphan frags on xmit") then added the frags orphan. Since an skb can be cloned on this tap to tap path, e.g., with a packet socket, I think the bug goes back to the original commit that introduced the first caller of skb_tx_error, commit 149d36f7187c ("tun: report orphan frags errors to zero copy callback") If respinning it may be worthile to link to this thread.