Re: [PATCH net v4 2/2] xsk: Fix zero-copy AF_XDP fragment drop
From: Jakub Kicinski <kuba@kernel.org>
Date: 2026-02-19 22:55:31
On Tue, 17 Feb 2026 21:08:51 +0000 Nikhil P. Rao wrote:
quoted hunk ↗ jump to hunk
AF_XDP should ensure that only a complete packet is sent to application. In the zero-copy case, if the Rx queue gets full as fragments are being enqueued, the remaining fragments are dropped. For the multi-buffer case, add a check to ensure that the Rx queue has enough space for all fragments of a packet before starting to enqueue them. Fixes: 24ea50127ecf ("xsk: support mbuf on ZC RX") Acked-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com> Signed-off-by: Nikhil P. Rao <redacted> --- net/xdp/xsk.c | 23 +++++++++++++++-------- 1 file changed, 15 insertions(+), 8 deletions(-)diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c index f2ec4f78bbb6..f7f816a5cb80 100644 --- a/net/xdp/xsk.c +++ b/net/xdp/xsk.c@@ -167,25 +167,32 @@ static int xsk_rcv_zc(struct xdp_sock *xs, struct xdp_buff *xdp, u32 len) struct xdp_buff_xsk *pos, *tmp; struct list_head *xskb_list; u32 contd = 0; + u32 num_desc; int err; - if (frags) + if (frags) { + num_desc = xdp_get_shared_info_from_buff(xdp)->nr_frags + 1; contd = XDP_PKT_CONTD;
[1]
+ } else {
+ err = __xsk_rcv_zc(xs, xskb, len, contd);
+ if (err)
+ goto err;
+ return 0;
+ }
- err = __xsk_rcv_zc(xs, xskb, len, contd);
- if (err)
+ if (xskq_prod_nb_free(xs->rx, num_desc) < num_desc) {
We can pull this check into the branch at [1]
It will let us preserve the existing flow.
Either that or handle the non-frag case fully upfront:
if (likely(!frags)) {
err = __xsk_rcv_zc(xs, xskb, len, 0);
if (err)
goto err;
return 0;
}
As is you have a weird mix of the two.
+ xs->rx_queue_full++; + err = -ENOBUFS; goto err; - if (likely(!frags)) - return 0; + } + __xsk_rcv_zc(xs, xskb, len, contd);
Personal preference perhaps but removing error checking always gives me pause. Maybe: bool frag_fail; frag_fail = __xsk_rcv_zc(xs, xskb, len, contd); list_for_each... ... frag_fail |= __xsk_rcv_zc(xs, xskb, len, contd); DEBUG_NET_WARN_ON_ONCE(frag_fail); ?
xskb_list = &xskb->pool->xskb_list;
list_for_each_entry_safe(pos, tmp, xskb_list, list_node) {
if (list_is_singular(xskb_list))
contd = 0;
len = pos->xdp.data_end - pos->xdp.data;
- err = __xsk_rcv_zc(xs, pos, len, contd);
- if (err)
- goto err;
+ __xsk_rcv_zc(xs, pos, len, contd);
list_del_init(&pos->list_node);
}
-- pw-bot: cr