null pointer dereference while loading i915

[Mihai Moldovan <ionic@ionic.de>]

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Hi Daniel, hi list

ever since version 3.2.0 (maybe even earlier, but 3.0.2 is still working fine),
my box is crashing when loading the i915 driver (mode-setting enabled.)

The current version I'm testing with is 3.5.0.

I was able to get the BUG output (please forgive any errors/flips in the output,
I have had to transcribe the messages from the screen/images), however, I'm not
able to find out what's wrong.

If I see it correctly, there's a null pointer dereference in a printk called
from inside gmbus_xfer. The only printk calls I can see in
drivers/gpu/drm/i915/intel_i2c.c gmbus_xfer() however are issued by the
DRM_DEBUG_KMS() and DRM_INFO() macros.
Neither call looks wrong to me, I even tried to swap adapter->name with
bus->adapter.name and make *sure* i < num is true, but haven't had any success.

I'd really like to see this bug fixed, as it's preventing me from updating the
kernel for over a year now.

Also, while 3.0.2 works, it *does* spew error/warning messages related to gmbus
and I've had corrupted VTs in the past (albeit after a long uptime with multiple
X restarting and DVI cable unplugging/reattaching events), so maybe there's a
lot more broken than "expected".

PCI-IDs:

00:02.0 VGA compatible controller [0300]: Intel Corporation 4 Series Chipset
Integrated Graphics Controller [8086:2e12] (rev 03) (prog-if 00 [VGA controller])
    Subsystem: Intel Corporation Device [8086:1003]
00:02.1 Display controller [0380]: Intel Corporation 4 Series Chipset Integrated
Graphics Controller [8086:2e13] (rev 03)
    Subsystem: Intel Corporation Device [8086:1003]

Messages are attached.

Any help is appreciated, thanks. :)

Best regards,


Mihai

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