netdev - Re: net: Detect drivers that reschedule NAPI and exhaust budget

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Date:	Fri, 19 Dec 2014 17:34:48 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	David Vrabel <david.vrabel@...rix.com>, netdev@...r.kernel.org,
	xen-devel@...ts.xenproject.org, konrad.wilk@...cle.com,
	boris.ostrovsky@...cle.com, edumazet@...gle.com,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: net: Detect drivers that reschedule NAPI and exhaust budget

On Sat, 2014-12-20 at 11:36 +1100, Herbert Xu wrote:
> On Sat, Dec 20, 2014 at 11:23:27AM +1100, Herbert Xu wrote:
> >
> > A similar bug exists in virtio_net.
> 
> In order to detect other drivers doing this we should add something
> like this.
> 
> -- >8 --
> The commit d75b1ade567ffab085e8adbbdacf0092d10cd09c (net: less
> interrupt masking in NAPI) required drivers to leave poll_list
> empty if the entire budget is consumed.
> 
> We have already had two broken drivers so let's add a check for
> this.
>  
> Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index f411c28..88f9725 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -4620,7 +4620,11 @@ static void net_rx_action(struct softirq_action *h)
>  					 */
>  					napi_gro_flush(n, HZ >= 1000);
>  				}
> -				list_add_tail(&n->poll_list, &repoll);
> +				/* Some drivers may have called napi_schedule
> +				 * prior to exhausting their budget.
> +				 */
> +				if (!WARN_ON_ONCE(!list_empty(&n->poll_list)))
> +					list_add_tail(&n->poll_list, &repoll);
>  			}
>  		}
>  

I do not think stack trace will point to the buggy driver ?

IMO it would be better to print a single line with the netdev name ?



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