On Tue, Jul 22, 2025 at 7:05 AM Jason Xing <[email protected]> wrote: > > On Mon, Jul 21, 2025 at 11:37 PM Stanislav Fomichev > <[email protected]> wrote: > > > > On 07/21, Jason Xing wrote: > > > From: Jason Xing <[email protected]> > > > > > > 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 <[email protected]> > > > --- > > > 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. > > Thanks for catching this! > > > Should we do 'for (; budget > 0; budget--)' > > instead? And maybe the same for ixgbe [0]? > > Not really. I think I can move the 'budget--' just before the > 'continue' part. If we convert it to use 'for' loop and then we end up > with one of 'break' statements, the budget still gets accidently > increased by one whereas ixgbe driver even doesn't handle the desc > this time. IIUC, it should not happen, right?
Sorry, I was totally wrong. Your suggestions work and I will revise them as you said :) Thanks, Jason
