On Sat, Sep 30, 2023 at 01:59:53PM +0200, Eric Dumazet wrote:

On Fri, Sep 22, 2023 at 1:13 PM Christian Marangi [off-list ref] wrote:

quoted

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@gmail.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 ?

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?

quoted

+static inline bool napi_is_scheduled(struct napi_struct *n)

const ...

Will change in v2. Thanks!

quoted

+{
+       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

-- 
	Ansuel