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

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Message-ID: <20150109022752.GA15785@gondor.apana.org.au>
Date:	Fri, 9 Jan 2015 13:27:52 +1100
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Dennis Chen <kernel.org.gnu@...il.com>
Cc:	netdev <netdev@...r.kernel.org>, davem@...emloft.net,
	eric.dumazet@...il.com
Subject: Re: [PATCH] net: Prevent multiple NAPI instances co-existing in the
 list

On Fri, Jan 09, 2015 at 10:24:18AM +0800, Dennis Chen wrote:
>
> Hi Herbert, please see this code piece in napi_poll:
> 
>      /* Some drivers may have called napi_schedule
>      * prior to exhausting their budget.
>      */
>     if (unlikely(!list_empty(&n->poll_list))) {
>         pr_warn_once("%s: Budget exhausted after napi rescheduled\n",
>                  n->dev ? n->dev->name : "backlog");
>         goto out_unlock;
>     }
> 
> Here "Some drivers" may have called  napi_schedule to make
> n->poll_list is not empty, does that mean "Some drivers" will clear
> NAPI_STATE_SCHED bit, otherwise the napi_schedule() will do nothing,
> does that make sense for you question? ;-)

No it tells me that you don't understand the problem at all.
Those drivers will end up resetting the NAPI_STATE_SCHED bit
after clearing it.

Cheers,
-- 
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
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