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SubjectRe: [git pull] DVB + ieee1394: firedtv driver


On Thu, 26 Feb 2009, Stefan Richter wrote:
>
> Alas I have no Linux box at hand before Saturday. I wonder, was
> ieee1394_bus_type not yet registered (i.e. ieee1394's ieee1394_init() not yet
> called) at the moment when fdtv_init is executed?
>
> Or what else could have been the NULL pointer dereference in driver_find?

Afaik, the only way that NULL pointer dereference can happen is if

struct kobject *k = kset_find_obj(bus->p->drivers_kset, name);

gets a NULL pointer exception either because of a NULL "bus" pointer as
the argument, or if "bus->p" is NULL.

And in this case, it's the latter. The Code: decode shows the whole
function in this case:

1c: 55 push %rbp
1d: 89 e5 mov %esp,%ebp
1f: e8 34 5f c8 ff callq 0xffffffffffc85f58
24: 89 c1 mov %eax,%ecx
26: 8b 42 38 mov 0x38(%rdx),%eax
29: 89 ca mov %ecx,%edx
2b:* 8b 40 54 mov 0x54(%rax),%eax <-- trapping instruction
2e: e8 6c 48 f9 ff callq 0xfffffffffff9489f
33: 31 d2 xor %edx,%edx
35: 85 c0 test %eax,%eax
37: 74 03 je 0x3c
39: 8b 50 6c mov 0x6c(%rax),%edx
3c: 5d pop %rbp
3d: 89 d0 mov %edx,%eax
3f: c3 retq
and that first "callq" seems to be due to Ingo having function tracing on,
while the second callq would have been that 'kset_find_obj()' thing.

So it does look like "&ieee1394_bus_type" has simply not been initialized
yet. It looks like ieee1394_init() is called too late.

Two choices that I can see:

- do the ieee1394_init() as a fs_initcall(), earlier

- move drivers/ieee1394 linking up to before drivers/media

but I suspect that drivers/media wants to be early, in order to do the
_media_ layer initialization early.

Does this work?

Linus

---
drivers/ieee1394/ieee1394_core.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/drivers/ieee1394/ieee1394_core.c b/drivers/ieee1394/ieee1394_core.c
index 1028e72..8723380 100644
--- a/drivers/ieee1394/ieee1394_core.c
+++ b/drivers/ieee1394/ieee1394_core.c
@@ -1275,7 +1275,7 @@ static void __exit ieee1394_cleanup(void)
unregister_chrdev_region(IEEE1394_CORE_DEV, 256);
}

-module_init(ieee1394_init);
+fs_initcall(ieee1394_init);
module_exit(ieee1394_cleanup);

/* Exported symbols */

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