netdev - Re: [PATCH net v2] net: fix race between napi kthread mode and busy poll

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Message-ID: <20210226164803.4413571f@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Fri, 26 Feb 2021 16:48:03 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Wei Wang <weiwan@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Martin Zaharinov <micron10@...il.com>,
        Alexander Duyck <alexanderduyck@...com>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>
Subject: Re: [PATCH net v2] net: fix race between napi kthread mode and busy
 poll

On Fri, 26 Feb 2021 16:30:47 -0800 Wei Wang wrote:
>  		thread = READ_ONCE(napi->thread);
>  		if (thread) {
> +			set_bit(NAPI_STATE_SCHED_THREADED, &napi->state);
>  			wake_up_process(thread);

What about the version which checks RUNNING? As long as
wake_up_process() implies a barrier I _think_ it should 
work as well. Am I missing some case, or did you decide
to go with the simpler/safer approach?