From: Herbert Xu <herbert@gondor.apana.org.au>
Date: Fri, 28 Mar 2008 23:25:26 +0000 (-0700)
Subject: [NET]: Add preemption point in qdisc_run
X-Git-Tag: v2.6.25-rc9~99^2~24
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2ba2506ca7ca62c56edaa334b0fe61eb5eab6ab0;p=linux-2.6

[NET]: Add preemption point in qdisc_run

The qdisc_run loop is currently unbounded and runs entirely in a
softirq.  This is bad as it may create an unbounded softirq run.

This patch fixes this by calling need_resched and breaking out if
necessary.

It also adds a break out if the jiffies value changes since that would
indicate we've been transmitting for too long which starves other
softirqs.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
---

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 10b5c0887f..b741618e4d 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -184,10 +184,22 @@ static inline int qdisc_restart(struct net_device *dev)
 
 void __qdisc_run(struct net_device *dev)
 {
-	do {
-		if (!qdisc_restart(dev))
+	unsigned long start_time = jiffies;
+
+	while (qdisc_restart(dev)) {
+		if (netif_queue_stopped(dev))
+			break;
+
+		/*
+		 * Postpone processing if
+		 * 1. another process needs the CPU;
+		 * 2. we've been doing it for too long.
+		 */
+		if (need_resched() || jiffies != start_time) {
+			netif_schedule(dev);
 			break;
-	} while (!netif_queue_stopped(dev));
+		}
+	}
 
 	clear_bit(__LINK_STATE_QDISC_RUNNING, &dev->state);
 }