Re: [net-next PATCH 1/3] net: introduce napi_is_scheduled helper

[Christian Marangi]

On Sat, Sep 30, 2023 at 01:59:53PM +0200, Eric Dumazet wrote:
> On Fri, Sep 22, 2023 at 1:13 PM Christian Marangi <ansuelsmth@xxxxxxxxx> wrote:
> >
> > We currently have napi_if_scheduled_mark_missed that can be used to
> > check if napi is scheduled but that does more thing than simply checking
> > it and return a bool. Some driver already implement custom function to
> > check if napi is scheduled.
> >
> > Drop these custom function and introduce napi_is_scheduled that simply
> > check if napi is scheduled atomically.
> >
> > Update any driver and code that implement a similar check and instead
> > use this new helper.
> >
> > Signed-off-by: Christian Marangi <ansuelsmth@xxxxxxxxx>
> > ---
> >  drivers/net/ethernet/chelsio/cxgb3/sge.c  | 8 --------
> >  drivers/net/wireless/realtek/rtw89/core.c | 2 +-
> >  include/linux/netdevice.h                 | 5 +++++
> >  net/core/dev.c                            | 2 +-
> >  4 files changed, 7 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/chelsio/cxgb3/sge.c b/drivers/net/ethernet/chelsio/cxgb3/sge.c
> > index 2e9a74fe0970..71fa2dc19034 100644
> > --- a/drivers/net/ethernet/chelsio/cxgb3/sge.c
> > +++ b/drivers/net/ethernet/chelsio/cxgb3/sge.c
> > @@ -2501,14 +2501,6 @@ static int napi_rx_handler(struct napi_struct *napi, int budget)
> >         return work_done;
> >  }
> >
> > -/*
> > - * Returns true if the device is already scheduled for polling.
> > - */
> > -static inline int napi_is_scheduled(struct napi_struct *napi)
> > -{
> > -       return test_bit(NAPI_STATE_SCHED, &napi->state);
> > -}
> > -
> >  /**
> >   *     process_pure_responses - process pure responses from a response queue
> >   *     @adap: the adapter
> > diff --git a/drivers/net/wireless/realtek/rtw89/core.c b/drivers/net/wireless/realtek/rtw89/core.c
> > index 133bf289bacb..bbf4ea3639d4 100644
> > --- a/drivers/net/wireless/realtek/rtw89/core.c
> > +++ b/drivers/net/wireless/realtek/rtw89/core.c
> > @@ -1744,7 +1744,7 @@ static void rtw89_core_rx_to_mac80211(struct rtw89_dev *rtwdev,
> >         struct napi_struct *napi = &rtwdev->napi;
> >
> >         /* In low power mode, napi isn't scheduled. Receive it to netif. */
> > -       if (unlikely(!test_bit(NAPI_STATE_SCHED, &napi->state)))
> > +       if (unlikely(!napi_is_scheduled(napi)))
> >                 napi = NULL;
> >
> >         rtw89_core_hw_to_sband_rate(rx_status);
> > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> > index db3d8429d50d..8eac00cd3b92 100644
> > --- a/include/linux/netdevice.h
> > +++ b/include/linux/netdevice.h
> > @@ -482,6 +482,11 @@ static inline bool napi_prefer_busy_poll(struct napi_struct *n)
> >         return test_bit(NAPI_STATE_PREFER_BUSY_POLL, &n->state);
> >  }
> >
> 
> 
> In which context is it safe to call this helper ?
>

test_bit is atomic so it should be always safe. Also the idea of this
check (and from what I can see this apply also to the other 2 user) is
somehow best effort, we check if in the current istant there is a napi
scheduled and we act.

> I fear that making this available will add more bugs.
> 
> For instance rspq_check_napi() seems buggy to me.
> 

Mhhh why? Am I opening a can of worms?

> > +static inline bool napi_is_scheduled(struct napi_struct *n)
> 
> const ...
> 

Will change in v2. Thanks!

> > +{
> > +       return test_bit(NAPI_STATE_SCHED, &n->state);
> > +}
> > +
> >  bool napi_schedule_prep(struct napi_struct *n);
> >
> >  /**
> > diff --git a/net/core/dev.c b/net/core/dev.c
> > index cc03a5758d2d..32ba8002f65a 100644
> > --- a/net/core/dev.c
> > +++ b/net/core/dev.c
> > @@ -6523,7 +6523,7 @@ static int __napi_poll(struct napi_struct *n, bool *repoll)
> >          * accidentally calling ->poll() when NAPI is not scheduled.
> >          */
> >         work = 0;
> > -       if (test_bit(NAPI_STATE_SCHED, &n->state)) {
> > +       if (napi_is_scheduled(n)) {
> >                 work = n->poll(n, weight);
> >                 trace_napi_poll(n, work, weight);
> >         }
> > --
> > 2.40.1
> >

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