Re: [2.6.5] Bad scheduling while atomic

[Stephen Hemminger <shemminger@xxxxxxxx>]

Bring up/down network devices with lapbether causes scheduling while
atomic (if preempt enabled).

The calls to rcu_read_lock are unnecessary since lapb_device_event 
is called from notifier with the rtnetlink semaphore held, it is
already protected from the labp_devices list changing.

Patch against 2.6.6-rc1

diff -Nru a/drivers/net/wan/lapbether.c b/drivers/net/wan/lapbether.c
--- a/drivers/net/wan/lapbether.c       Fri Apr 16 11:00:35 2004
+++ b/drivers/net/wan/lapbether.c       Fri Apr 16 11:00:35 2004
@@ -392,6 +392,8 @@
 
 /*
  *     Handle device status changes.
+ *
+ * Called from notifier with RTNL held.
  */
 static int lapbeth_device_event(struct notifier_block *this,
                                unsigned long event, void *ptr)
@@ -402,7 +404,6 @@
        if (!dev_is_ethdev(dev))
                return NOTIFY_DONE;
 
-       rcu_read_lock();
        switch (event) {
        case NETDEV_UP:
                /* New ethernet device -> new LAPB interface     */
@@ -422,7 +423,6 @@
                        lapbeth_free_device(lapbeth);
                break;
        }
-       rcu_read_unlock();
 
        return NOTIFY_DONE;
 }