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Message-Id: <20251017143103.2620164-3-maciej.fijalkowski@intel.com>
Date: Fri, 17 Oct 2025 16:31:03 +0200
From: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To: bpf@...r.kernel.org,
ast@...nel.org,
daniel@...earbox.net,
hawk@...nel.org,
ilias.apalodimas@...aro.org,
toke@...hat.com,
lorenzo@...nel.org,
kuba@...nel.org
Cc: netdev@...r.kernel.org,
magnus.karlsson@...el.com,
andrii@...nel.org,
stfomichev@...il.com,
aleksander.lobakin@...el.com,
Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Subject: [PATCH v2 bpf 2/2] veth: update mem type in xdp_buff
Veth calls skb_pp_cow_data() which makes the underlying memory to
originate from system page_pool. For CONFIG_DEBUG_VM=y and XDP program
that uses bpf_xdp_adjust_tail(), following splat was observed:
[ 32.204881] BUG: Bad page state in process test_progs pfn:11c98b
[ 32.207167] page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x11c98b
[ 32.210084] flags: 0x1fffe0000000000(node=0|zone=1|lastcpupid=0x7fff)
[ 32.212493] raw: 01fffe0000000000 dead000000000040 ff11000123c9b000 0000000000000000
[ 32.218056] raw: 0000000000000000 0000000000000001 00000000ffffffff 0000000000000000
[ 32.220900] page dumped because: page_pool leak
[ 32.222636] Modules linked in: bpf_testmod(O) bpf_preload
[ 32.224632] CPU: 6 UID: 0 PID: 3612 Comm: test_progs Tainted: G O 6.17.0-rc5-gfec474d29325 #6969 PREEMPT
[ 32.224638] Tainted: [O]=OOT_MODULE
[ 32.224639] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
[ 32.224641] Call Trace:
[ 32.224644] <IRQ>
[ 32.224646] dump_stack_lvl+0x4b/0x70
[ 32.224653] bad_page.cold+0xbd/0xe0
[ 32.224657] __free_frozen_pages+0x838/0x10b0
[ 32.224660] ? skb_pp_cow_data+0x782/0xc30
[ 32.224665] bpf_xdp_shrink_data+0x221/0x530
[ 32.224668] ? skb_pp_cow_data+0x6d1/0xc30
[ 32.224671] bpf_xdp_adjust_tail+0x598/0x810
[ 32.224673] ? xsk_destruct_skb+0x321/0x800
[ 32.224678] bpf_prog_004ac6bb21de57a7_xsk_xdp_adjust_tail+0x52/0xd6
[ 32.224681] veth_xdp_rcv_skb+0x45d/0x15a0
[ 32.224684] ? get_stack_info_noinstr+0x16/0xe0
[ 32.224688] ? veth_set_channels+0x920/0x920
[ 32.224691] ? get_stack_info+0x2f/0x80
[ 32.224693] ? unwind_next_frame+0x3af/0x1df0
[ 32.224697] veth_xdp_rcv.constprop.0+0x38a/0xbe0
[ 32.224700] ? common_startup_64+0x13e/0x148
[ 32.224703] ? veth_xdp_rcv_one+0xcd0/0xcd0
[ 32.224706] ? stack_trace_save+0x84/0xa0
[ 32.224709] ? stack_depot_save_flags+0x28/0x820
[ 32.224713] ? __resched_curr.constprop.0+0x332/0x3b0
[ 32.224716] ? timerqueue_add+0x217/0x320
[ 32.224719] veth_poll+0x115/0x5e0
[ 32.224722] ? veth_xdp_rcv.constprop.0+0xbe0/0xbe0
[ 32.224726] ? update_load_avg+0x1cb/0x12d0
[ 32.224730] ? update_cfs_group+0x121/0x2c0
[ 32.224733] __napi_poll+0xa0/0x420
[ 32.224736] net_rx_action+0x901/0xe90
[ 32.224740] ? run_backlog_napi+0x50/0x50
[ 32.224743] ? clockevents_program_event+0x1cc/0x280
[ 32.224746] ? hrtimer_interrupt+0x31e/0x7c0
[ 32.224749] handle_softirqs+0x151/0x430
[ 32.224752] do_softirq+0x3f/0x60
[ 32.224755] </IRQ>
It's because xdp_rxq with mem model set to MEM_TYPE_PAGE_SHARED was used
when initializing xdp_buff.
Fix this by using new helper xdp_convert_skb_to_buff() that, besides
init/prepare xdp_buff, will check if page used for linear part of
xdp_buff comes from page_pool. We assume that linear data and frags will
have same memory provider as currently XDP API does not provide us a way
to distinguish it (the mem model is registered for *whole* Rx queue and
here we speak about single buffer granularity).
In order to meet expected skb layout by new helper, pull the mac header
before conversion from skb to xdp_buff.
However, that is not enough as before releasing xdp_buff out of veth via
XDP_{TX,REDIRECT}, mem type on xdp_rxq associated with xdp_buff is
restored to its original model. We need to respect previous setting at
least until buff is converted to frame, as frame carries the mem_type.
Add a page_pool variant of veth_xdp_get() so that we avoid refcount
underflow when draining page frag.
Fixes: 0ebab78cbcbf ("net: veth: add page_pool for page recycling")
Reported-by: Alexei Starovoitov <ast@...nel.org>
Closes: https://lore.kernel.org/bpf/CAADnVQ+bBofJDfieyOYzSmSujSfJwDTQhiz3aJw7hE+4E2_iPA@mail.gmail.com/
Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
---
drivers/net/veth.c | 43 +++++++++++++++++++++++++++----------------
1 file changed, 27 insertions(+), 16 deletions(-)
diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index a3046142cb8e..eeeee7bba685 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -733,7 +733,7 @@ static void veth_xdp_rcv_bulk_skb(struct veth_rq *rq, void **frames,
}
}
-static void veth_xdp_get(struct xdp_buff *xdp)
+static void veth_xdp_get_shared(struct xdp_buff *xdp)
{
struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp);
int i;
@@ -746,12 +746,33 @@ static void veth_xdp_get(struct xdp_buff *xdp)
__skb_frag_ref(&sinfo->frags[i]);
}
+static void veth_xdp_get_pp(struct xdp_buff *xdp)
+{
+ struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp);
+ int i;
+
+ page_pool_ref_page(virt_to_page(xdp->data));
+ if (likely(!xdp_buff_has_frags(xdp)))
+ return;
+
+ for (i = 0; i < sinfo->nr_frags; i++) {
+ skb_frag_t *frag = &sinfo->frags[i];
+
+ page_pool_ref_page(netmem_to_page(frag->netmem));
+ }
+}
+
+static void veth_xdp_get(struct xdp_buff *xdp)
+{
+ xdp->rxq->mem.type == MEM_TYPE_PAGE_POOL ?
+ veth_xdp_get_pp(xdp) : veth_xdp_get_shared(xdp);
+}
+
static int veth_convert_skb_to_xdp_buff(struct veth_rq *rq,
struct xdp_buff *xdp,
struct sk_buff **pskb)
{
struct sk_buff *skb = *pskb;
- u32 frame_sz;
if (skb_shared(skb) || skb_head_is_locked(skb) ||
skb_shinfo(skb)->nr_frags ||
@@ -762,19 +783,9 @@ static int veth_convert_skb_to_xdp_buff(struct veth_rq *rq,
skb = *pskb;
}
- /* SKB "head" area always have tailroom for skb_shared_info */
- frame_sz = skb_end_pointer(skb) - skb->head;
- frame_sz += SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
- xdp_init_buff(xdp, frame_sz, &rq->xdp_rxq);
- xdp_prepare_buff(xdp, skb->head, skb_headroom(skb),
- skb_headlen(skb), true);
+ __skb_pull(*pskb, skb->data - skb_mac_header(skb));
- if (skb_is_nonlinear(skb)) {
- skb_shinfo(skb)->xdp_frags_size = skb->data_len;
- xdp_buff_set_frags_flag(xdp);
- } else {
- xdp_buff_clear_frags_flag(xdp);
- }
+ xdp_convert_skb_to_buff(skb, xdp, &rq->xdp_rxq);
*pskb = skb;
return 0;
@@ -822,24 +833,24 @@ static struct sk_buff *veth_xdp_rcv_skb(struct veth_rq *rq,
case XDP_TX:
veth_xdp_get(xdp);
consume_skb(skb);
- xdp->rxq->mem = rq->xdp_mem;
if (unlikely(veth_xdp_tx(rq, xdp, bq) < 0)) {
trace_xdp_exception(rq->dev, xdp_prog, act);
stats->rx_drops++;
goto err_xdp;
}
stats->xdp_tx++;
+ rq->xdp_rxq.mem = rq->xdp_mem;
rcu_read_unlock();
goto xdp_xmit;
case XDP_REDIRECT:
veth_xdp_get(xdp);
consume_skb(skb);
- xdp->rxq->mem = rq->xdp_mem;
if (xdp_do_redirect(rq->dev, xdp, xdp_prog)) {
stats->rx_drops++;
goto err_xdp;
}
stats->xdp_redirect++;
+ rq->xdp_rxq.mem = rq->xdp_mem;
rcu_read_unlock();
goto xdp_xmit;
default:
--
2.43.0
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