Re: Kernel crash when using systemtap

[Padmanabhan S N <paddusn at yahoo dot com>]

The stap .c file is about 16M in size and the generated .ko is about 13M.


The script is very simple, but traces all functions in our module :


probe module("_our_module_").function("*").call {
??????? printf("%s %s %s %s\n", thread_indent(1), "->",? probefunc(), $$parms);
}

probe module("_our_module_").function("*").inline {
??????? printf("%s %s %s %s\n", thread_indent(1), "->",? probefunc(), $$parms);
??????? thread_indent(-1);
}

probe module("_our_module_").function("*").return {
??????? printf("%s %s %s %s\n", thread_indent(-1), "<-",? probefunc(), $$return);
}


I did try removing the inline probes. But that doesnt help.?

Narrowing down the wildcards will limit the scope of tracing, right ?. And we are pretty much tied to RHEL 5.5 at this moment.?

Is there anything else that I can try ?


~Padhu.



----- Original Message -----
From: Frank Ch. Eigler <fche@redhat.com>
To: Padmanabhan S N <paddusn@yahoo.com>
Cc: "systemtap@sourceware.org" <systemtap@sourceware.org>
Sent: Monday, July 18, 2011 12:37 PM
Subject: Re: Kernel crash when using systemtap


Padmanabhan S N <paddusn@yahoo.com> writes:

> While using systemtap to do function call tracing (.call,
> .inline. .return probes) on one of our proprietary kernel modules,
> the system crashes. [...]

OK.

> The environment is RHEL 5.5 64-bit. I've tried to look at the crash
> dump, and it does point to the generated systemtap module. But I
> couldn't proceed beyond that. Here is a bt from one of the crash dumps.
>
> [...]
> #4 [ffff8100956f1af0] add_to_page_cache at ffffffff8000c722
> #5 [ffff8100956f1b48] _stp_map_get_ii at ffffffff889d8459 [stap_44a2f6019f0e29a88c9470c55950ae1a_14041197]
> [...]

How big is this module?? That _14041197 string makes it sound large.
Can you share the script source?? Consider removing the .inline
probes, or narrow the wildcards and/or pretty-printing.? Consider
testing out an updated kernel; IIRC there have been kprobes robustness
improvements.

- FChE