bridge: don't allow setting hello time to zero

Dushan Tcholich reports that on his system ksoftirqd can consume
between %6 to %10 of cpu time, and cause ~200 context switches per
second.

He then correlated this with a report by bdupree@techfinesse.com:

	http://marc.info/?l=linux-kernel&m=119613299024398&w=2

and the culprit cause seems to be starting the bridge interface.
In particular, when starting the bridge interface, his scripts
are specifying a hello timer interval of "0".

The bridge hello time can't be safely set to values less than 1
second, otherwise it is possible to end up with a runaway timer.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 18 insertions, 8 deletions

diff --git a/net/bridge/br_sysfs_br.c b/net/bridge/br_sysfs_br.c
index 27d6a511c8c1..158dee8b4965 100644
--- a/net/bridge/br_sysfs_br.c
+++ b/net/bridge/br_sysfs_br.c
@@ -29,11 +29,12 @@
  */
 static ssize_t store_bridge_parm(struct device *d,
                                  const char *buf, size_t len,
-                                 void (*set)(struct net_bridge *, unsigned long))
+                                 int (*set)(struct net_bridge *, unsigned long))
 {
         struct net_bridge *br = to_bridge(d);
         char *endp;
         unsigned long val;
+        int err;
 
         if (!capable(CAP_NET_ADMIN))
                 return -EPERM;
@@ -43,9 +44,9 @@ static ssize_t store_bridge_parm(struct device *d,
                 return -EINVAL;
 
         spin_lock_bh(&br->lock);
-        (*set)(br, val);
+        err = (*set)(br, val);
         spin_unlock_bh(&br->lock);
-        return len;
+        return err ? err : len;
 }
 
 
@@ -56,12 +57,13 @@ static ssize_t show_forward_delay(struct device *d,
         return sprintf(buf, "%lu\n", jiffies_to_clock_t(br->forward_delay));
 }
 
-static void set_forward_delay(struct net_bridge *br, unsigned long val)
+static int set_forward_delay(struct net_bridge *br, unsigned long val)
 {
         unsigned long delay = clock_t_to_jiffies(val);
         br->forward_delay = delay;
         if (br_is_root_bridge(br))
                 br->bridge_forward_delay = delay;
+        return 0;
 }
 
 static ssize_t store_forward_delay(struct device *d,
@@ -80,12 +82,17 @@ static ssize_t show_hello_time(struct device *d, struct device_attribute *attr,
                        jiffies_to_clock_t(to_bridge(d)->hello_time));
 }
 
-static void set_hello_time(struct net_bridge *br, unsigned long val)
+static int set_hello_time(struct net_bridge *br, unsigned long val)
 {
         unsigned long t = clock_t_to_jiffies(val);
+
+        if (t < HZ)
+                return -EINVAL;
+
         br->hello_time = t;
         if (br_is_root_bridge(br))
                 br->bridge_hello_time = t;
+        return 0;
 }
 
 static ssize_t store_hello_time(struct device *d,
@@ -104,12 +111,13 @@ static ssize_t show_max_age(struct device *d, struct device_attribute *attr,
                        jiffies_to_clock_t(to_bridge(d)->max_age));
 }
 
-static void set_max_age(struct net_bridge *br, unsigned long val)
+static int set_max_age(struct net_bridge *br, unsigned long val)
 {
         unsigned long t = clock_t_to_jiffies(val);
         br->max_age = t;
         if (br_is_root_bridge(br))
                 br->bridge_max_age = t;
+        return 0;
 }
 
 static ssize_t store_max_age(struct device *d, struct device_attribute *attr,
@@ -126,9 +134,10 @@ static ssize_t show_ageing_time(struct device *d,
         return sprintf(buf, "%lu\n", jiffies_to_clock_t(br->ageing_time));
 }
 
-static void set_ageing_time(struct net_bridge *br, unsigned long val)
+static int set_ageing_time(struct net_bridge *br, unsigned long val)
 {
         br->ageing_time = clock_t_to_jiffies(val);
+        return 0;
 }
 
 static ssize_t store_ageing_time(struct device *d,
@@ -180,9 +189,10 @@ static ssize_t show_priority(struct device *d, struct device_attribute *attr,
                        (br->bridge_id.prio[0] << 8) | br->bridge_id.prio[1]);
 }
 
-static void set_priority(struct net_bridge *br, unsigned long val)
+static int set_priority(struct net_bridge *br, unsigned long val)
 {
         br_stp_set_bridge_priority(br, (u16) val);
+        return 0;
 }
 
 static ssize_t store_priority(struct device *d, struct device_attribute *attr,