On Sat, 10 Apr 2021 00:29:23 +0300 Claudiu Manoil wrote:
> On 09.04.2021 22:27, Vladimir Oltean wrote:
> > From: Vladimir Oltean <vladimir.olt...@nxp.com>
> >
> > The blamed commit introduced a bit in the TX software buffer descriptor
> > structure for determining whether a BD is final or not; we rearm the TX
> > interrupt vector for every frame (hence final BD) transmitted.
> >
> > But there is a problem with the patch: it replaced a condition whose
> > expression is a bool which was evaluated at the beginning of the "while"
> > loop with a bool expression that is evaluated on the spot: tx_swbd->is_eof.
> >
> > The problem with the latter expression is that the tx_swbd has already
> > been incremented at that stage, so the tx_swbd->is_eof check is in fact
> > with the _next_ software BD. Which is _not_ final.
> >
> > The effect is that the CPU is in 100% load with ksoftirqd because it
> > does not acknowledge the TX interrupt, so the handler keeps getting
> > called again and again.
> >
> > The fix is to restore the code structure, and keep the local bool is_eof
> > variable, just to assign it the tx_swbd->is_eof value instead of
> > !!tx_swbd->skb.
> >
> > Fixes: d504498d2eb3 ("net: enetc: add a dedicated is_eof bit in the TX
> > software BD")
> > Reported-by: Alex Marginean <alexandru.margin...@nxp.com>
> > Signed-off-by: Vladimir Oltean <vladimir.olt...@nxp.com>
>
> Reviewed-by: Claudiu Manoil <claudiu.man...@nxp.com>
Applied, thanks!
