> -----Original Message-----
> From: Intel-wired-lan <[email protected]> On Behalf
> Of Jason Xing
> Sent: Tuesday, July 22, 2025 3:51 PM
> To: Nguyen, Anthony L <[email protected]>; Kitszel,
> Przemyslaw <[email protected]>; [email protected];
> [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; Karlsson, Magnus
> <[email protected]>; Fijalkowski, Maciej
> <[email protected]>; [email protected];
> [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; [email protected];
> [email protected]
> Cc: [email protected]; [email protected];
> [email protected]; [email protected]; Jason Xing
> <[email protected]>
> Subject: [Intel-wired-lan] [PATCH net v2 1/2] stmmac: xsk: fix
> underflow of budget in zerocopy mode
>
> From: Jason Xing <[email protected]>
>
> An underflow can happen when the budget number of descs are consumed.
> as long as the budget is decreased to zero, it will again go into
> while (budget-- > 0) statement and get decreased by one, so the
> underflow issue can happen. It will lead to returning true whereas the
> expected value should be false.
>
> In this case where all the budget is used up, it means zc function
> should return false to let the poll run again because normally we
> might have more data to process. Without this patch, zc function would
> return true instead.
>
> Fixes: 132c32ee5bc0 ("net: stmmac: Add TX via XDP zero-copy socket")
> Signed-off-by: Jason Xing <[email protected]>
Reviewed-by: Aleksandr Loktionov <[email protected]>
> ---
> v2
> Link: https://lore.kernel.org/all/20250721083343.16482-1-
> [email protected]/
> 1. target net tree instead of net-next
> 2. revise commit message
> 3. use for loop to replace while loop
> ---
> drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index f350a6662880..c4cd4526ba05 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -2596,7 +2596,7 @@ static bool stmmac_xdp_xmit_zc(struct
> stmmac_priv *priv, u32 queue, u32 budget)
>
> budget = min(budget, stmmac_tx_avail(priv, queue));
>
> - while (budget-- > 0) {
> + for (; budget > 0; budget--)
> struct stmmac_metadata_request meta_req;
> struct xsk_tx_metadata *meta = NULL;
> dma_addr_t dma_addr;
> --
> 2.41.3
