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net/mlx5e: Prevent stale XSK buffer release on refill retry

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When an XDP redirect to an AF_XDP socket fails because its RX ring is
full, the XSK core frees the buffer. During the subsequent batched refill
of a legacy cyclic RQ, mlx5e also releases the WQE's XSK buffer before
allocating a replacement. If that refill succeeds only partially, a WQE
left without a replacement retains its old buffer pointer.

The buffer can meanwhile be allocated to another WQE. A later refill
retry can then free the live buffer through the stale pointer and publish
the same UMEM frame twice.

Mark the WQE as released immediately after the driver-side free. The flag
is already cleared when a replacement buffer is assigned, so refill
retries no longer release stale pointers.

The failure is silent and produces no kernel warning or splat. A
standalone legacy cyclic-RQ zero-copy libxsk reproducer, using 64-byte UDP
traffic offered at 12 Mpps, detected it: stock stopped after 2,854,914
packets in 4.094 seconds, with 4,542 xdp_rx_ring_full events and 64
ownership/double-publication errors. With this change it processed
356,904,225 packets in 30 seconds despite 571,405 xdp_rx_ring_full events,
with no ownership or data errors.

Fixes: 3f93f82988 ("net/mlx5e: RX, Defer page release in legacy rq for better recycling")
Cc: stable@vger.kernel.org
Suggested-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Signed-off-by: Jerome Tollet <jtollet@cisco.com>
Link: https://patch.msgid.link/20260824141645.23700-2-jtollet@cisco.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Jerome Tollet 2026-08-24 16:16:44 +02:00 committed by Jakub Kicinski
parent a5d946466a
commit e01620844c
1 changed files with 5 additions and 2 deletions
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7
drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
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@ -410,8 +410,11 @@ static inline void mlx5e_free_rx_wqe(struct mlx5e_rq *rq,
static void mlx5e_xsk_free_rx_wqe(struct mlx5e_wqe_frag_info *wi)
{
if (!(wi->flags & BIT(MLX5E_WQE_FRAG_SKIP_RELEASE)))
xsk_buff_free(*wi->xskp);
if (wi->flags & BIT(MLX5E_WQE_FRAG_SKIP_RELEASE))
return;
xsk_buff_free(*wi->xskp);
wi->flags |= BIT(MLX5E_WQE_FRAG_SKIP_RELEASE);
}
static void mlx5e_dealloc_rx_wqe(struct mlx5e_rq *rq, u16 ix)