[Linux-stm32] [PATCH net-next 1/2] stmmac: xsk: fix underflow of budget in zerocopy mode

[Stanislav Fomichev]

On 07/21, Jason Xing wrote:
> From: Jason Xing <kernelxing at tencent.com>
> 
> The issue 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 are used up, it means zc function
> should return false to let the poll run again because normally we
> might have more data to process.
> 
> Fixes: 132c32ee5bc0 ("net: stmmac: Add TX via XDP zero-copy socket")
> Signed-off-by: Jason Xing <kernelxing at tencent.com>
> ---
>  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index f350a6662880..ea5541f9e9a6 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) {
> +	while (budget > 0) {

There is a continue on line 2621. Should we do 'for (; budget > 0; budget--)'
instead? And maybe the same for ixgbe [0]?

0: https://lore.kernel.org/netdev/20250720091123.474-3-kerneljasonxing@gmail.com/