netdev - Re: [PATCH] net: Prevent multiple NAPI instances co-existing in the list

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Date:	Thu, 08 Jan 2015 16:04:08 +0300
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Dennis Chen <kernel.org.gnu@...il.com>,
	netdev <netdev@...r.kernel.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Miller <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH] net: Prevent multiple NAPI instances co-existing in the
 list

Hello.

On 1/8/2015 11:22 AM, Dennis Chen wrote:

> Some drivers may clear the NAPI_STATE_SCHED bit upon the state of the
> NAPI instance after exhaust the budget in the poll function, which
> will open a window for next device interrupt handler to insert a same
> instance to the list after calling list_add_tail(&n->poll_list,
> repoll) if we don't set this bit.

> Signed-off-by: Dennis Chen <kernel.org.gnu@...il.com>
> ---
>   net/core/dev.c |    8 ++++++++
>   1 file changed, 8 insertions(+)

> diff --git a/net/core/dev.c b/net/core/dev.c
> index 683d493..b3107ac 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -4619,6 +4619,14 @@ static int napi_poll(struct napi_struct *n,
> struct list_head *repoll)
>                               n->dev ? n->dev->name : "backlog");
>                  goto out_unlock;
>          }
> +
> +       /* Some drivers may exit the polling mode when exhaust the

    s/exhaust/exhausting/.

> +        * budget. Set the NAPI_STATE_SCHED bit to prevent multiple NAPI
> +        * instances in the list in case of next device interrupt raised.
> +        */
> +       if (unlikely(!test_and_set_bit(NAPI_STATE_SCHED, &n->state)))
> +               pr_warn_once("%s: exit polling mode after exhaust the budget\n",

    Likewise. And s/exit/exiting/.

WBR, Sergei

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