[Bug 9750] [patch 2.6.25 v2] dev: avoid a race that triggers assertion failure

[Bug 9750] [patch 2.6.25 v2] dev: avoid a race that triggers assertion failure

[Matti Linnanvuori]

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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>

---





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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-2.6.25/net/core/dev.c	2008-02-12 12:37:51.206833000 +0200
+++ b/net/core/dev.c	2008-02-13 09:01:25.697592900 +0200
@@ -1071,8 +1071,6 @@ 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,
@@ -1083,6 +1081,8 @@ 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

Re: [Bug 9750] [patch 2.6.25 v2] dev: avoid a race that triggers assertion failure

[David Miller]

From: Matti Linnanvuori <mattilinnanvuori@yahoo.com>
Date: Tue, 12 Feb 2008 23:06:41 -0800 (PST)

> 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>

Patch applied, thanks.