Re: 2.6.17-rc5-mm1

[Ingo Molnar]

* Ingo Molnar <mingo@xxxxxxx> wrote:

> Martin, is the box still somewhat operational after such a crash? If 
> yes then we could use my crash-tracer to see the kernel function call 
> history leading up to the crash:
> 
>   http://redhat.com/~mingo/lockdep-patches/latency-tracing-lockdep.patch
> 
> just apply the patch, accept the offered Kconfig defaults and it will 
> be configured to do the trace-crashes thing. Reproduce the crash and 
> save /proc/latency_trace - it contains the execution history leading 
> up to the crash. (on the CPU that crashes) Should work on i386 and 
> x86_64.
> 
> the trace is saved upon the first crash or lockdep assert that occurs 
> on the box. (but you'll have lockdep disabled, so it's the crash that 
> matters)

i just provoked a NULL pointer dereference with the tracer applied, and 
/proc/latency_trace contained the proper trace, leading up to the crash:

gettimeo-2333  0D... 2210us : trace_hardirqs_on (restore_nocheck)
gettimeo-2333  0.... 2210us > sys_gettimeofday (00000000 00000000 0000007b)
gettimeo-2333  0.... 2210us : sys_gettimeofday (sysenter_past_esp)
gettimeo-2333  0D... 2211us : do_page_fault (error_code)
gettimeo-2333  0D... 2211us : do_page_fault (c0123238 0 2)
gettimeo-2333  0D... 2211us : do_page_fault (10202 202 7b)
gettimeo-2333  0D... 2211us : trace_hardirqs_on (do_page_fault)
gettimeo-2333  0.... 2211us : lockdep_acquire (do_page_fault)

for best trace output you should have KALLSYMS and KALLSYMS_ALL enabled.

of course it could happen that tracing makes your crash go away ...

	Ingo
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