netdev - Re: [RFC net-next 1/3] net: provide macros for commonly copied lockless queue stop/wake code

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Message-ID: <ZCuZj9b2s3FI9tzo@gondor.apana.org.au>
Date:   Tue, 4 Apr 2023 11:29:19 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
        pabeni@...hat.com, alexanderduyck@...com, roman.gushchin@...ux.dev,
        kuba@...nel.org
Subject: Re: [RFC net-next 1/3] net: provide macros for commonly copied
 lockless queue stop/wake code

Jakub Kicinski <kuba@...nel.org> wrote:
>
> +#define netif_tx_queue_try_stop(txq, get_desc, start_thrs)             \
> +       ({                                                              \
> +               int _res;                                               \
> +                                                                       \
> +               netif_tx_stop_queue(txq);                               \
> +                                                                       \
> +               smp_mb();                                               \

We should never have an smp_mb by itself.  It must come with a
comment indicating which other barrier (possibly implicit) it
pairs with.

I know that you're just copying old code around, but by turning
it into a helper, we should treat it as new code and apply the
current requirements.

Thanks,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt