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Subject[PATCH] Bug Fix: 2.6.{5,6}: i8042 module unload bug
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Date

I've reported this bug 3 days ago. But since it is still not yet
fixed in the new 2.6.6, I'm reposting this.


Dan> I've successfully and repeated hanged vanilla 2.6.5 kernel.
Dan> Here is how I do it:

Dan> 1) Configure and compile kernel (on Intel x86) so that
Dan> 'serio', 'i8042', 'atkbd' are all modules. i.e.
Dan> CONFIG_SERIO_I8042=m CONFIG_SERIO=m CONFIG_KEYBOARD_ATKBD=m

Dan> 2) Boot the compiled kernel.
Dan> 3) Log in from network.
Dan> 4) modprobe the following modules in order: serio, i8042, atkbd
Dan> 5) Now, keyboard works, as expected.
Dan> 6) rmmod i8042 ===> hangs. CAPSLOCK doesn't respond (of
Dan> course, i8042 is rmoved), machine doesn't respond to ping
Dan> (why?), although my PCMCIA network card still blinks and the
Dan> hardware indicate of PCMCIA activity also blinks. But
Dan> (un)plugging the PCMCIA card gives no response.

Dan> The same is observed in 2.6.6-rc3.

The same is also observed in 2.6.6.


I've found and fixed the bug.

It has nothing to do with module dependencies. Rather, it's a bug
with improper shutdown of a timer.


Cause: When the i8042 module is unloaded, the i8042_exit() shuts down
it timer by calling del_timer_sync(). However, after that
call, there can still be interrupts from the i8042 chip (due to
keyboard or mouse activities). Such interrupts invoke the
interrupt handler i8042_interrupt(), which would call
mod_timer() to reschedule a new timer event. But i8042_exit()
won't want for this new timer event. It may exit before the
event arrives. The module is unloaded as i8042_exit() exits,
but this can happen before the new timer event comes. As a
result, when the timer expires, the kernel tries to call
i8042_timer_func(), which has been unloaded! This results in a
complete freeze.

The Fix: is to make sure interrupts from the i8042 chip are disabled
before calling del_timer_sync() to clean up the timer. In
i8042_exit(), this is as easy as swapping the order of the
calls to del_timer_sync() and i8042_controller_cleanup().


The Patch:



--- linux-2.6.6-vanilla/drivers/input/serio/i8042.c 2004/05/06 13:24:46 1.1
+++ linux-2.6.6/drivers/input/serio/i8042.c 2004/05/06 15:17:50 1.2
@@ -990,24 +990,28 @@
unregister_reboot_notifier(&i8042_notifier);

if (i8042_pm_dev)
pm_unregister(i8042_pm_dev);

if (i8042_sysdev_initialized) {
sysdev_unregister(&device_i8042);
sysdev_class_unregister(&kbc_sysclass);
}

- del_timer_sync(&i8042_timer);
-
i8042_controller_cleanup();

+ /* we must delete the timer AFTER the i8042 chip is cleaned up,
+ so as to prevent any more interrupts to invoke i8042_interrupt()
+ which then schedules newer timer events.
+ */
+ del_timer_sync(&i8042_timer);
+
if (i8042_kbd_values.exists)
serio_unregister_port(&i8042_kbd_port);

if (i8042_aux_values.exists)
serio_unregister_port(&i8042_aux_port);

for (i = 0; i < 4; i++)
if (i8042_mux_values[i].exists)
serio_unregister_port(i8042_mux_port + i);




--
Sau Dan LEE 李守敦(Big5) ~{@nJX6X~}(HZ)
E-mail: danlee@informatik.uni-freiburg.de
Home page: http://www.informatik.uni-freiburg.de/~danlee

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