netdev - Re: [net-next PATCH 1/3] net: introduce napi_is

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Date: Sat, 30 Sep 2023 13:59:53 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Christian Marangi <ansuelsmth@...il.com>
Cc: Vincent Whitchurch <vincent.whitchurch@...s.com>, Raju Rangoju <rajur@...lsio.com>, 
	"David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Alexandre Torgue <alexandre.torgue@...s.st.com>, Jose Abreu <joabreu@...opsys.com>, 
	Maxime Coquelin <mcoquelin.stm32@...il.com>, Ping-Ke Shih <pkshih@...ltek.com>, 
	Kalle Valo <kvalo@...nel.org>, Simon Horman <horms@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Jiri Pirko <jiri@...nulli.us>, 
	Hangbin Liu <liuhangbin@...il.com>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-stm32@...md-mailman.stormreply.com, 
	linux-arm-kernel@...ts.infradead.org, linux-wireless@...r.kernel.org
Subject: Re: [net-next PATCH 1/3] net: introduce napi_is_scheduled helper

On Fri, Sep 22, 2023 at 1:13 PM Christian Marangi <ansuelsmth@...il.com> 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@...il.com>
> ---
>  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 ?

I fear that making this available will add more bugs.

For instance rspq_check_napi() seems buggy to me.

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

const ...

> +{
> +       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
>