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Tue, 19 May 2026 17:43:17 -0700 (PDT) Received: from KERNELXING-MC1.tencent.com ([2408:8207:1923:2c20:f1df:d520:8103:19c8]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-36951059f4dsm14746277a91.0.2026.05.19.17.43.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 19 May 2026 17:43:16 -0700 (PDT) From: Jason Xing To: davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, bjorn@kernel.org, magnus.karlsson@intel.com, maciej.fijalkowski@intel.com, jonathan.lemon@gmail.com, sdf@fomichev.me, ast@kernel.org, daniel@iogearbox.net, hawk@kernel.org, john.fastabend@gmail.com, horms@kernel.org, andrew+netdev@lunn.ch Cc: bpf@vger.kernel.org, netdev@vger.kernel.org, Jason Xing Subject: [PATCH net v4 3/5] xsk: drain continuation descs after overflow in xsk_build_skb() Date: Wed, 20 May 2026 08:42:42 +0800 Message-Id: <20260520004244.55663-4-kerneljasonxing@gmail.com> X-Mailer: git-send-email 2.33.0 In-Reply-To: <20260520004244.55663-1-kerneljasonxing@gmail.com> References: <20260520004244.55663-1-kerneljasonxing@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Jason Xing When a multi-buffer packet exceeds MAX_SKB_FRAGS and triggers -EOVERFLOW, only the current descriptor is released from the TX ring. The remaining continuation descriptors of the same packet stay in the ring. Since xs->skb is set to NULL after the drop, the TX loop picks up these leftover frags and misinterprets each one as the beginning of a new packet, corrupting the packet stream. Fix this by adding a drain_cont flag to xdp_sock. When overflow occurs and the dropped descriptor has XDP_PKT_CONTD set, the flag is raised, so we have a chance to examine and handle the potential remaining descs of this big overflow'ed skb. When the last fragment (without XDP_PKT_CONTD) is processed, the flag is cleared and the loop continues to process subsequent descriptors with the remaining budget. This behavior follows how previous xmit path treats overflow packets. Closes: https://lore.kernel.org/all/20260425041726.85FB3C2BCB2@smtp.kernel.org/ Fixes: cf24f5a5feea ("xsk: add support for AF_XDP multi-buffer on Tx path") Signed-off-by: Jason Xing --- include/net/xdp_sock.h | 1 + net/xdp/xsk.c | 19 +++++++++++++++++++ 2 files changed, 20 insertions(+) diff --git a/include/net/xdp_sock.h b/include/net/xdp_sock.h index ebac60a3d8a1..8b51876efbed 100644 --- a/include/net/xdp_sock.h +++ b/include/net/xdp_sock.h @@ -80,6 +80,7 @@ struct xdp_sock { * call of __xsk_generic_xmit(). */ struct sk_buff *skb; + bool drain_cont; struct list_head map_list; /* Protects map_list */ diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c index 0a6203c42576..f4add7be8c93 100644 --- a/net/xdp/xsk.c +++ b/net/xdp/xsk.c @@ -1062,11 +1062,30 @@ static int __xsk_generic_xmit(struct sock *sk) goto out; } + if (unlikely(xs->drain_cont)) { + unsigned long flags; + u32 idx; + + spin_lock_irqsave(&xs->pool->cq_prod_lock, flags); + idx = xskq_get_prod(xs->pool->cq); + xskq_prod_write_addr(xs->pool->cq, idx, desc.addr); + xskq_prod_submit_n(xs->pool->cq, 1); + spin_unlock_irqrestore(&xs->pool->cq_prod_lock, flags); + + xs->tx->invalid_descs++; + xskq_cons_release(xs->tx); + if (!xp_mb_desc(&desc)) + xs->drain_cont = false; + continue; + } + skb = xsk_build_skb(xs, &desc); if (IS_ERR(skb)) { err = PTR_ERR(skb); if (err != -EOVERFLOW) goto out; + if (xp_mb_desc(&desc)) + xs->drain_cont = true; err = 0; continue; } -- 2.43.7