Re: Bug in BCMA: device_unregister causing "NULL pointer dereference at"

From: RafaÅ MiÅecki
Date: Thu Jul 21 2011 - 03:26:22 EST

W dniu 7 lipca 2011 17:25 uÅytkownik RafaÅ MiÅecki <zajec5@xxxxxxxxx> napisaÅ:
> I've problem with bcma and bus subsystem.
> This works fine:
> modprobe bcma; rmmod bcma
> This:
> modprobe bcma; modprobe b43; rmmod b43; rmmod bcma
> causes:
> BUG: unable to handle kernel NULL pointer dereference at  (null)
> My BCMA has only 3 fores, out of them only 1 is registered as device:
> bcma: Core 0 found: ChipCommon (manuf 0x4BF, id 0x800, rev 0x22, class 0x0)
> bcma: Core 1 found: IEEE 802.11 (manuf 0x4BF, id 0x812, rev 0x17, class 0x0)
> bcma: Core 2 found: PCIe (manuf 0x4BF, id 0x820, rev 0x0F, class 0x0)
> The dereference comes out from
> static void bcma_unregister_cores(struct bcma_bus *bus)
> There is a simple loop:
> list_for_each_entry(core, &bus->cores, list) {
> Â Â Â Âif (core->dev_registered)
> Â Â Â Â Â Â Â Âdevice_unregister(&core->dev);
> }
> So when I unload bcma after I got driver (b43) for 0x812 core, I get
> NULL pointer dereference.
> Any tip, why does it happen?

I've tracked where does crash really happen (kobject_del does not
really say much). The real forwardtrace is:
device_unregister â device_del â kobject_del â kobj_kset_leave â
kobj_kset_leave â list_del_init

If you take a look at list_del_init, it touches "prev" and "next". So
I've added some debugging:
pr_info("core->dev.kobj.entry.prev: 0x%p\n", core->dev.kobj.entry.prev);
pr_info("core-> 0x%p\n", core->;

modprobe bcma && rmmod bcma:
[ 342.866366] bcma: Unregistering device for core 0x812
[ 342.866380] bcma: core->dev.kobj.entry.prev: 0xdb82780c
[ 342.866382] bcma: core-> 0xda044980

modprobe bcma && modprobe b43 && rmmod b43 && rmmod bcma:
[ 612.819306] bcma: Unregistering device for core 0x812
[ 612.819320] bcma: core->dev.kobj.entry.prev: 0x (null)
[ 612.819322] bcma: core-> 0xd7fe6614
[ 612.819971] BUG: unable to handle kernel NULL pointer dereference at (null)
[ 612.819989] IP: [<c03dcfbe>] kobject_del+0x2e/0x60

I've no idea why kobj entry list gets corrupted after loading b43
driver supporting device for core 0x812.

Any help now maybe?

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