linux-kernel - RE: [PATCH net 1/8] net: enetc: fix the off-by-one issue in enetc_map_tx

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Message-ID:
 <PAXPR04MB8510AA1D5B596B4382873A9F88FA2@PAXPR04MB8510.eurprd04.prod.outlook.com>
Date: Tue, 18 Feb 2025 02:11:12 +0000
From: Wei Fang <wei.fang@....com>
To: Michal Swiatkowski <michal.swiatkowski@...ux.intel.com>
CC: Claudiu Manoil <claudiu.manoil@....com>, Vladimir Oltean
	<vladimir.oltean@....com>, Clark Wang <xiaoning.wang@....com>,
	"andrew+netdev@...n.ch" <andrew+netdev@...n.ch>, "davem@...emloft.net"
	<davem@...emloft.net>, "edumazet@...gle.com" <edumazet@...gle.com>,
	"kuba@...nel.org" <kuba@...nel.org>, "pabeni@...hat.com" <pabeni@...hat.com>,
	Ioana Ciornei <ioana.ciornei@....com>, "Y.B. Lu" <yangbo.lu@....com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"imx@...ts.linux.dev" <imx@...ts.linux.dev>, "stable@...r.kernel.org"
	<stable@...r.kernel.org>
Subject: RE: [PATCH net 1/8] net: enetc: fix the off-by-one issue in
 enetc_map_tx_buffs()

> > Fixes: d4fd0404c1c9 ("enetc: Introduce basic PF and VF ENETC ethernet
> drivers")
> > Cc: stable@...r.kernel.org
> > Signed-off-by: Wei Fang <wei.fang@....com>
> > ---
> >  drivers/net/ethernet/freescale/enetc/enetc.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c
> b/drivers/net/ethernet/freescale/enetc/enetc.c
> > index 6a6fc819dfde..f7bc2fc33a76 100644
> > --- a/drivers/net/ethernet/freescale/enetc/enetc.c
> > +++ b/drivers/net/ethernet/freescale/enetc/enetc.c
> > @@ -372,13 +372,13 @@ static int enetc_map_tx_buffs(struct enetc_bdr
> *tx_ring, struct sk_buff *skb)
> >  dma_err:
> >  	dev_err(tx_ring->dev, "DMA map error");
> >
> > -	do {
> > +	while (count--) {
> >  		tx_swbd = &tx_ring->tx_swbd[i];
> >  		enetc_free_tx_frame(tx_ring, tx_swbd);
> >  		if (i == 0)
> >  			i = tx_ring->bd_count;
> >  		i--;
> > -	} while (count--);
> > +	};
> 
> In enetc_lso_hw_offload() this is fixed by --count instead of changing
> to while and count--, maybe follow this scheme, or event better call
> helper function to fix in one place.

The situation is slightly different in enetc_map_tx_buffs(), the count
may be 0 when the error occurs. But in enetc_lso_hw_offload(), the
count will not be 0 when the error occurs.

> 
> The same problem is probably in enetc_map_tx_tso_buffs().
> 

I think there is no such problem in enetc_map_tx_tso_buffs(),
because the index 'i' has been increased before the error occurs,
but the count is not increased, so the actual 'count' is count + 1.