netdev - Re: [PATCH net] net: Use NAPI_* in test

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Message-ID: <20250911064021.026ad6f2@kernel.org>
Date: Thu, 11 Sep 2025 06:40:21 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Samiullah Khawaja <skhawaja@...gle.com>
Cc: "David S . Miller " <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, willemb@...gle.com,
 netdev@...r.kernel.org, mkarsten@...terloo.ca
Subject: Re: [PATCH net] net: Use NAPI_* in test_bit when stopping napi
 kthread

On Wed, 10 Sep 2025 20:37:16 +0000 Samiullah Khawaja wrote:
> napi_stop_kthread waits for the NAPI_STATE_SCHED_THREADED to be unset
> before stopping the kthread. But it uses test_bit with the
> NAPIF_STATE_SCHED_THREADED and that might stop the kthread early before
> the flag is unset.
> 
> Use the NAPI_* variant of the NAPI state bits in test_bit instead.
> 
> Tested:
>  ./tools/testing/selftests/net/nl_netdev.py
>  TAP version 13
>  1..7
>  ok 1 nl_netdev.empty_check
>  ok 2 nl_netdev.lo_check
>  ok 3 nl_netdev.page_pool_check
>  ok 4 nl_netdev.napi_list_check
>  ok 5 nl_netdev.dev_set_threaded
>  ok 6 nl_netdev.napi_set_threaded
>  ok 7 nl_netdev.nsim_rxq_reset_down
>  # Totals: pass:7 fail:0 xfail:0 xpass:0 skip:0 error:0
> 
>  ./tools/testing/selftests/drivers/net/napi_threaded.py
>  TAP version 13
>  1..2
>  ok 1 napi_threaded.change_num_queues
>  ok 2 napi_threaded.enable_dev_threaded_disable_napi_threaded
>  # Totals: pass:2 fail:0 xfail:0 xpass:0 skip:0 error:0
> 
> Fixes: 689883de94dd ("net: stop napi kthreads when THREADED napi is disabled")
> Signed-off-by: Samiullah Khawaja <skhawaja@...gle.com>

Is this basically addressing the bug that Martin run into?

> diff --git a/net/core/dev.c b/net/core/dev.c
> index 93a25d87b86b..8d49b2198d07 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -6965,7 +6965,7 @@ static void napi_stop_kthread(struct napi_struct *napi)
>  	 * the kthread.
>  	 */
>  	while (true) {
> -		if (!test_bit(NAPIF_STATE_SCHED_THREADED, &napi->state))
> +		if (!test_bit(NAPI_STATE_SCHED_THREADED, &napi->state))
>  			break;
>  
>  		msleep(20);