[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>

1 files changed, 15 insertions, 3 deletions

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 10b5c0887fff..b741618e4d54 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);
 }