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xsk: drain continuation descs after overflow in xsk_build_skb()

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Fix generic xmit path multi-buffer logic when packets are either too big
(count of descriptors exceed MAX_SKB_FRAGS) or an invalid descriptor is
included in fragmented packet. Introduce xdp_sock::drain_cont and act
upon this flag - when it is set, keep on consuming descriptors from
AF_XDP Tx ring and put them directly onto Cq. Previously these
descriptors were silently lost and could never be reached again.

Fixes: cf24f5a5fe ("xsk: add support for AF_XDP multi-buffer on Tx path")
Closes: https://lore.kernel.org/all/20260425041726.85FB3C2BCB2@smtp.kernel.org/
Reviewed-by: Jason Xing <kernelxing@tencent.com>
Co-developed-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com> # wrapped cq addr submission onto routine
Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: Jason Xing <kernelxing@tencent.com>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20260719135609.147823-3-maciej.fijalkowski@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Jason Xing
2026-07-24 15:12:14 -07:00
committed by Jakub Kicinski
parent a3c8382ebc
commit bd44a6dcd4
2 changed files with 43 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files
include/net/xdp_sock.h
+1
View File
@@ -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 */
net/xdp/xsk.c
+42 -3
View File
@@ -737,6 +737,19 @@ static void xsk_cq_submit_addr_locked(struct xsk_buff_pool *pool,
spin_unlock_irqrestore(&pool->cq_prod_lock, flags);
}
static void xsk_cq_submit_addr_single_locked(struct xsk_buff_pool *pool,
struct xdp_desc *desc)
{
unsigned long flags;
u32 idx;
spin_lock_irqsave(&pool->cq_prod_lock, flags);
idx = xskq_get_prod(pool->cq);
xskq_prod_write_addr(pool->cq, idx, desc->addr);
xskq_prod_submit_n(pool->cq, 1);
spin_unlock_irqrestore(&pool->cq_prod_lock, flags);
}
static void xsk_cq_cancel_locked(struct xsk_buff_pool *pool, u32 n)
{
spin_lock(&pool->cq->cq_cached_prod_lock);
@@ -1028,13 +1041,14 @@ free_err:
static int __xsk_generic_xmit(struct sock *sk)
{
struct xdp_sock *xs = xdp_sk(sk);
bool sent_frame = false;
struct xdp_desc desc;
struct sk_buff *skb;
u32 cached_cons;
u32 max_batch;
int err = 0;
mutex_lock(&xs->mutex);
cached_cons = xs->tx->cached_cons;
/* Since we dropped the RCU read lock, the socket state might have changed. */
if (unlikely(!xsk_is_bound(xs))) {
@@ -1063,11 +1077,21 @@ static int __xsk_generic_xmit(struct sock *sk)
goto out;
}
if (unlikely(xs->drain_cont)) {
xsk_cq_submit_addr_single_locked(xs->pool, &desc);
xs->tx->invalid_descs++;
xskq_cons_release(xs->tx);
xs->drain_cont = xp_mb_desc(&desc);
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;
}
@@ -1096,18 +1120,33 @@ static int __xsk_generic_xmit(struct sock *sk)
goto out;
}
sent_frame = true;
xs->skb = NULL;
}
if (xskq_has_descs(xs->tx)) {
bool drain = xs->skb || xs->drain_cont || xp_mb_desc(&desc);
err = xsk_cq_reserve_locked(xs->pool);
if (err) {
xs->tx->invalid_descs--;
if (xs->skb)
xsk_drop_skb(xs->skb);
xs->drain_cont = drain;
err = -EAGAIN;
goto out;
}
if (xs->skb)
xsk_drop_skb(xs->skb);
xsk_cq_submit_addr_single_locked(xs->pool, &desc);
xskq_cons_release(xs->tx);
xs->drain_cont = xp_mb_desc(&desc);
}
out:
if (sent_frame)
if (xs->tx->cached_cons != cached_cons)
__xsk_tx_release(xs);
mutex_unlock(&xs->mutex);