[PATCH 6.18 044/333] net/mlx5e: RX, Fix XDP multi-buf frag counting for legacy RQ

Greg Kroah-Hartman
2026-03-17T17:07:14Z

From: Dragos Tatulea <dtatulea@nvidia.com>

[ Upstream commit a6413e6f6c9d9bb9833324cb3753582f7bc0f2fa ]

XDP multi-buf programs can modify the layout of the XDP buffer when the
program calls bpf_xdp_pull_data() or bpf_xdp_adjust_tail(). The
referenced commit in the fixes tag corrected the assumption in the mlx5
driver that the XDP buffer layout doesn't change during a program
execution. However, this fix introduced another issue: the dropped
fragments still need to be counted on the driver side to avoid page
fragment reference counting issues.

Such issue can be observed with the
test_xdp_native_adjst_tail_shrnk_data selftest when using a payload of
3600 and shrinking by 256 bytes (an upcoming selftest patch): the last
fragment gets released by the XDP code but doesn't get tracked by the
driver. This results in a negative pp_ref_count during page release and
the following splat:

WARNING: include/net/page_pool/helpers.h:297 at mlx5e_page_release_fragmented.isra.0+0x4a/0x50 [mlx5_core], CPU#12: ip/3137
Modules linked in: [...]
CPU: 12 UID: 0 PID: 3137 Comm: ip Not tainted 6.19.0-rc3+ #12 NONE
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
RIP: 0010:mlx5e_page_release_fragmented.isra.0+0x4a/0x50 [mlx5_core]
[...]
Call Trace:
<TASK>
mlx5e_dealloc_rx_wqe+0xcb/0x1a0 [mlx5_core]
mlx5e_free_rx_descs+0x7f/0x110 [mlx5_core]
mlx5e_close_rq+0x50/0x60 [mlx5_core]
mlx5e_close_queues+0x36/0x2c0 [mlx5_core]
mlx5e_close_channel+0x1c/0x50 [mlx5_core]
mlx5e_close_channels+0x45/0x80 [mlx5_core]
mlx5e_safe_switch_params+0x1a5/0x230 [mlx5_core]
mlx5e_change_mtu+0xf3/0x2f0 [mlx5_core]
netif_set_mtu_ext+0xf1/0x230
do_setlink.isra.0+0x219/0x1180
rtnl_newlink+0x79f/0xb60
rtnetlink_rcv_msg+0x213/0x3a0
netlink_rcv_skb+0x48/0xf0
netlink_unicast+0x24a/0x350
netlink_sendmsg+0x1ee/0x410
__sock_sendmsg+0x38/0x60
____sys_sendmsg+0x232/0x280
___sys_sendmsg+0x78/0xb0
__sys_sendmsg+0x5f/0xb0
[...]
do_syscall_64+0x57/0xc50

This patch fixes the issue by doing page frag counting on all the
original XDP buffer fragments for all relevant XDP actions (XDP_TX ,
XDP_REDIRECT and XDP_PASS). This is basically reverting to the original
counting before the commit in the fixes tag.

As frag_page is still pointing to the original tail, the nr_frags
parameter to xdp_update_skb_frags_info() needs to be calculated
in a different way to reflect the new nr_frags.

Fixes: afd5ba577c10 ("net/mlx5e: RX, Fix generating skb from non-linear xdp_buff for legacy RQ")
Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Amery Hung <ameryhung@gmail.com>
Link: https://patch.msgid.link/20260305142634.1813208-6-tariqt@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/ethernet/mellanox/mlx5/core/en_rx.c | 11 ++++-------
1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
index 348c451473cd6..2ffa4e6b8c373 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
@@ -1759,6 +1759,7 @@ mlx5e_skb_from_cqe_nonlinear(struct mlx5e_rq *rq, struct mlx5e_wqe_frag_info *wi
struct skb_shared_info *sinfo;
u32 frag_consumed_bytes;
struct bpf_prog *prog;
+ u8 nr_frags_free = 0;
struct sk_buff *skb;
dma_addr_t addr;
u32 truesize;
@@ -1801,15 +1802,13 @@ mlx5e_skb_from_cqe_nonlinear(struct mlx5e_rq *rq, struct mlx5e_wqe_frag_info *wi

prog = rcu_dereference(rq->xdp_prog);
if (prog) {
- u8 nr_frags_free, old_nr_frags = sinfo->nr_frags;
+ u8 old_nr_frags = sinfo->nr_frags;

if (mlx5e_xdp_handle(rq, prog, mxbuf)) {
if (__test_and_clear_bit(MLX5E_RQ_FLAG_XDP_XMIT,
rq->flags)) {
struct mlx5e_wqe_frag_info *pwi;

- wi -= old_nr_frags - sinfo->nr_frags;
-
for (pwi = head_wi; pwi < wi; pwi++)
pwi->frag_page->frags++;
}
@@ -1817,10 +1816,8 @@ mlx5e_skb_from_cqe_nonlinear(struct mlx5e_rq *rq, struct mlx5e_wqe_frag_info *wi
}

nr_frags_free = old_nr_frags - sinfo->nr_frags;
- if (unlikely(nr_frags_free)) {
- wi -= nr_frags_free;
+ if (unlikely(nr_frags_free))
truesize -= nr_frags_free * frag_info->frag_stride;
- }
}

skb = mlx5e_build_linear_skb(
@@ -1836,7 +1833,7 @@ mlx5e_skb_from_cqe_nonlinear(struct mlx5e_rq *rq, struct mlx5e_wqe_frag_info *wi

if (xdp_buff_has_frags(&mxbuf->xdp)) {
/* sinfo->nr_frags is reset by build_skb, calculate again. */
- xdp_update_skb_frags_info(skb, wi - head_wi - 1,
+ xdp_update_skb_frags_info(skb, wi - head_wi - nr_frags_free - 1,
sinfo->xdp_frags_size, truesize,
xdp_buff_get_skb_flags(&mxbuf->xdp));

--
2.51.0