linux-kernel - Re: [net-next PATCH v2 3/4] netdev: replace napi_reschedule with napi

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Message-ID: <65205789.5d0a0220.7e49b.ccb0@mx.google.com>
Date:   Fri, 6 Oct 2023 20:52:57 +0200
From:   Christian Marangi <ansuelsmth@...il.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     Jakub Kicinski <kuba@...nel.org>, Jason Gunthorpe <jgg@...pe.ca>,
        Leon Romanovsky <leon@...nel.org>,
        Wolfgang Grandegger <wg@...ndegger.com>,
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Subject: Re: [net-next PATCH v2 3/4] netdev: replace napi_reschedule with
 napi_schedule

On Thu, Oct 05, 2023 at 06:41:03PM +0200, Eric Dumazet wrote:
> On Thu, Oct 5, 2023 at 6:32 PM Jakub Kicinski <kuba@...nel.org> wrote:
> >
> > On Thu, 5 Oct 2023 18:11:56 +0200 Eric Dumazet wrote:
> > > OK, but I suspect some users of napi_reschedule() might not be race-free...
> >
> > What's the race you're thinking of?
> 
> This sort of thing... the race is in fl_starving() though...
> 
> diff --git a/drivers/net/ethernet/chelsio/cxgb4/sge.c
> b/drivers/net/ethernet/chelsio/cxgb4/sge.c
> index 98dd78551d89..b5ff2e1a9975 100644
> --- a/drivers/net/ethernet/chelsio/cxgb4/sge.c
> +++ b/drivers/net/ethernet/chelsio/cxgb4/sge.c
> @@ -4261,7 +4261,7 @@ static void sge_rx_timer_cb(struct timer_list *t)
> 
>                         if (fl_starving(adap, fl)) {
>                                 rxq = container_of(fl, struct sge_eth_rxq, fl);
> -                               if (napi_reschedule(&rxq->rspq.napi))
> +                               if (napi_schedule(&rxq->rspq.napi))
>                                         fl->starving++;
>                                 else
>                                         set_bit(id, s->starving_fl);

Ehhh problem is that this is a simple rename so if any race is present,
it's already there and not caused by this rename :(

Don't know maybe this is out of scope and should be investigated with a
bug report?

Maybe this should be changed to prep/__schedule to prevent any kind of
race? But doing so doesn't prevent any kind of ""starving""?

-- 
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