Re: Segfault on module load --SuSE kernel source

[Philippe E. <ph...@wa...>]

Scott Gifford wrote:
> Philippe,
> There are no messages from oprofile in /var/log/messages, only the 
> oops.  I have seen the messages you speak of when the module loads.  
> I've put some debug messages in op_apic.c and op_fixmap.c. They tell me 
> that it does fail at the first apic_read() call in enable_apic in 
> op_apic.c. Here's the trail:
> May 12 08:56:33 mynode kernel: oprofile: Entered apic_setup
> May 12 08:56:33 mynode kernel: oprofile: Entered fixmap_setup
> May 12 08:56:33 mynode kernel: oprofile: Did rdmsr op_apic.enable_apic.
> May 12 08:56:33 mynode kernel: oprofile: Just before apic_read.enable_apic.
> May 12 08:56:33 mynode kernel: Unable to handle kernel paging request at 
> virtual address ffffe030
> May 12 08:56:33 mynode kernel:  printing eip:
> 
> You mentioned that the APIC may not be enabled.  How can I check that?

At the start of dmesg you must find something like

Local APIC disabled by BIOS -- reenabling.
Found and enabled local APIC!

or later in dmesg output:

Using local APIC timer interrupts.
calibrating APIC timer ...

If something goes wrong you must see:

Could not enable APIC!

In this case it's not suprising we segfault, try the attached
patch to look if the apic is correctly enabled. Oprofile will
fall back to rtc mode if apic is not enabled so it's not a
proper fix ...


regards,
Phil