netdev - [PATCH 3/4] net: Always poll at least one device in net_rx

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Message-Id: <E1Y2QRs-0001q5-6u@gondolin.me.apana.org.au>
Date:	Sun, 21 Dec 2014 07:16:24 +1100
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	David Miller <davem@...emloft.net>, 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: [PATCH 3/4] net: Always poll at least one device in net_rx_action

We should only perform the softnet_break check after we have polled
at least one device in net_rx_action.  Otherwise a zero or negative
setting of netdev_budget can lock up the whole system.

Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
---

 net/core/dev.c |    7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 4a9c424..22b0fb2 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4634,16 +4634,15 @@ static void net_rx_action(struct softirq_action *h)
 	while (!list_empty(&list)) {
 		struct napi_struct *n;
 
+		n = list_first_entry(&list, struct napi_struct, poll_list);
+		budget -= napi_poll(n, &repoll);
+
 		/* If softirq window is exhausted then punt.
 		 * Allow this to run for 2 jiffies since which will allow
 		 * an average latency of 1.5/HZ.
 		 */
 		if (unlikely(budget <= 0 || time_after_eq(jiffies, time_limit)))
 			goto softnet_break;
-
-
-		n = list_first_entry(&list, struct napi_struct, poll_list);
-		budget -= napi_poll(n, &repoll);
 	}
 
 	if (!sd_has_rps_ipi_waiting(sd) &&
--
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