netdev - Re: [PATCH net-next] net: stop napi kthreads when THREADED napi is disabled

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Message-ID: <20250513170844.03ef5752@kernel.org>
Date: Tue, 13 May 2025 17:08:44 -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>,
 almasrymina@...gle.com, willemb@...gle.com, jdamato@...tly.com,
 mkarsten@...terloo.ca, weiwan@...gle.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] net: stop napi kthreads when THREADED napi is
 disabled

On Tue, 13 May 2025 00:26:31 +0000 Samiullah Khawaja wrote:
> @@ -7463,6 +7482,15 @@ static int napi_thread_wait(struct napi_struct *napi)
>  			return 0;
>  		}
>  
> +		/* Since the SCHED_THREADED is not set so we do not own this
> +		 * napi and it is safe to stop here if we are asked to. Checking
> +		 * the SCHED_THREADED before stopping here makes sure that this
> +		 * napi was not schedule again while napi threaded was being
> +		 * disabled.
> +		 */

Not sure if this works:

          CPU 0 (IRQ)             CPU 1 (NAPI thr)          CPU 2 (config)

  ____napi_schedule()
    if (test_bit(NAPI_STATE_THREADED))

                                                         clear_bit(NAPI_STATE_THREADED)
                                                         kthread_stop(thread)

                              if (test_bit(NAPI_STATE_SCHED_THREADED))
                                   ..
                              if (kthread_should_stop())
                                   exit

       set_bit(NAPI_STATE_SCHED_THREADED)
       wake_up_process(thread);

> +		if (kthread_should_stop())
> +			break;
> +
>  		schedule();
>  		set_current_state(TASK_INTERRUPTIBLE);