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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20141220065529.GA2033@gondor.apana.org.au>
Date:	Sat, 20 Dec 2014 17:55:29 +1100
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	David Miller <davem@...emloft.net>
Cc:	eric.dumazet@...il.com, david.vrabel@...rix.com,
	netdev@...r.kernel.org, xen-devel@...ts.xenproject.org,
	konrad.wilk@...cle.com, boris.ostrovsky@...cle.com,
	edumazet@...gle.com
Subject: Re: net: Detect drivers that reschedule NAPI and exhaust budget

On Fri, Dec 19, 2014 at 09:40:00PM -0500, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Fri, 19 Dec 2014 17:34:48 -0800
> 
> >> @@ -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 ?
> 
> Right, we are already back from the poll routine and will just end
> up seeing the call trace leading to the software interrupt.

Good point Eric.

-- >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..47fdc5c 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4620,7 +4620,13 @@ 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 (unlikely(!list_empty(&n->poll_list)))
+					pr_warn("%s: Budget exhausted after napi rescheduled\n", n->dev ? n->dev->name : "backlog");
+				else
+					list_add_tail(&n->poll_list, &repoll);
 			}
 		}
 
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
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html