From: Maciej Fijalkowski <maciej.fijalkowski@intel•com>
To: Jason Xing <kerneljasonxing@gmail•com>
Cc: <davem@davemloft•net>, <edumazet@google•com>, <kuba@kernel•org>,
<pabeni@redhat•com>, <bjorn@kernel•org>,
<magnus.karlsson@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>, <bpf@vger•kernel.org>,
<netdev@vger•kernel.org>, Jason Xing <kernelxing@tencent•com>
Subject: Re: [PATCH net v4 3/5] xsk: drain continuation descs after overflow in xsk_build_skb()
Date: Wed, 20 May 2026 18:10:31 +0200 [thread overview]
Message-ID: <ag3c9/EF4h7DLQu3@boxer> (raw)
In-Reply-To: <20260520004244.55663-4-kerneljasonxing@gmail.com>
On Wed, May 20, 2026 at 08:42:42AM +0800, Jason Xing wrote:
> From: Jason Xing <kernelxing@tencent•com>
>
> 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 <kernelxing@tencent•com>
> ---
> 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)) {
Hi Jason,
could we get away from introducing dedicated boolean to xdp_sock for
handling this rare case?
> + 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);
It feels a bit off to do this cleanup one-by-one.
I wonder if it could be covered by xsk_drop_skb() where you would walk the
tx ring and store addrs at xsk_addrs and then use xsk_cq_submit_addr_locked() ?
OTOH, in theory the amount of frags after we hit the overflow case could
be well over MAX_SKB_FRAGS again so xsk_addrs wouldn't be able to cover
them.
> +
> + 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
>
next prev parent reply other threads:[~2026-05-20 16:10 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-20 0:42 [PATCH net v4 0/5] xsk: fix meta and publish of cq issues Jason Xing
2026-05-20 0:42 ` [PATCH net v4 1/5] xsk: cache csum_start/csum_offset to fix TOCTOU in xsk_skb_metadata() Jason Xing
2026-05-21 12:04 ` Maciej Fijalkowski
2026-05-20 0:42 ` [PATCH net v4 2/5] xsk: fix buffer leak in xsk_drop_skb() for AF_XDP multi-buffer Tx Jason Xing
2026-05-21 12:05 ` Maciej Fijalkowski
2026-05-20 0:42 ` [PATCH net v4 3/5] xsk: drain continuation descs after overflow in xsk_build_skb() Jason Xing
2026-05-20 16:10 ` Maciej Fijalkowski [this message]
2026-05-20 23:53 ` Jason Xing
2026-05-21 12:02 ` Maciej Fijalkowski
2026-05-21 13:10 ` Jason Xing
2026-05-22 9:06 ` Magnus Karlsson
2026-05-22 9:22 ` Jason Xing
2026-05-20 0:42 ` [PATCH net v4 4/5] xsk: drain continuation descs on invalid descriptor in __xsk_generic_xmit() Jason Xing
2026-05-20 0:42 ` [PATCH net v4 5/5] selftests/xsk: drain CQ to wait for TX completion Jason Xing
2026-05-21 12:23 ` [PATCH net v4 0/5] xsk: fix meta and publish of cq issues Maciej Fijalkowski
2026-05-21 12:41 ` Jason Xing
2026-05-21 12:59 ` Maciej Fijalkowski
2026-05-21 13:07 ` Jason Xing
2026-05-21 14:24 ` Maciej Fijalkowski
2026-05-22 8:55 ` Jason Xing
2026-05-22 13:48 ` Jason Xing
2026-05-22 18:33 ` Maciej Fijalkowski
2026-05-22 23:49 ` Jason Xing
2026-05-26 19:43 ` Maciej Fijalkowski
2026-05-26 23:26 ` Jason Xing
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