[Bug 9750] [patch 2.6.24] dev: avoid a race that triggers assertion failure

[Bug 9750] [patch 2.6.24] dev: avoid a race that triggers assertion failure

[Matti Linnanvuori]

From: Matti Linnanvuori <mattilinnanvuori@yahoo.com>

There is a race in Linux kernel file net/core/dev.c, function dev_close.
The function calls function dev_deactivate, which calls function
dev_watchdog_down that deletes the watchdog timer. However, after that, a
driver can call netif_carrier_ok, which calls function
__netdev_watchdog_up that can add the watchdog timer again. Function
unregister_netdevice calls function dev_shutdown that traps the bug
!timer_pending(&dev->watchdog_timer). Moving dev_deactivate after
netif_running() has been cleared prevents function netif_carrier_on
from calling __netdev_watchdog_up and adding the watchdog timer again.

Signed-off-by: Matti Linnanvuori <mattilinnanvuori@yahoo.com>

---

--- linux-2.6.24/net/core/dev.c    2008-01-23 08:20:55.733012300 +0200
+++ b/net/core/dev.c    2008-01-23 08:24:32.818766600 +0200
@@ -1068,8 +1068,6 @@ int dev_close(struct net_device *dev)
      */
     call_netdevice_notifiers(NETDEV_GOING_DOWN, dev);
 
-    dev_deactivate(dev);
-
     clear_bit(__LINK_STATE_START, &dev->state);
 
     /* Synchronize to scheduled poll. We cannot touch poll list,
@@ -1080,6 +1078,8 @@ int dev_close(struct net_device *dev)
      */
     smp_mb__after_clear_bit(); /* Commit netif_running(). */
 
+    dev_deactivate(dev);
+
     /*
      *    Call the device specific close. This cannot fail.
      *    Only if device is UP





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