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printk in kernel.function("__switch_to") probe crashes machine


3. I have written a kernel function probe in __switch_to and find that I can define it as:
probe kernel.function("__switch_to")
{
print("calling ITrace_switch\n");
// ITrace_switch()
}
If I run this script I get:
Running sudo /usr/bin/staprun -u dcn -d 3614 -c "/home/dcn/itrace/ITrace_test/hanoi/hanoi64 -2" /tmp/stapAiagsM/pitrace.ko
start itrace
calling ITrace_switch
....
calling ITrace_switch
end itrace
and this works just as expected.
However, if I uncomment ITrace_switch() call in my __switch_to probe, and define it as:
function ITrace_switch()
%{
printk("ITrace_switch called\n");
%}
this crashes the machine.


I'm a SystemTap novice, and kernel novice so I'm not sure if there is some obvious reason why this "printk" should cause the system to crash. There are no messages on the console.

If there is a simple explanation I guess it might help me avoid doing this sort of thing in the future. For now, I'll just avoid using printk in this scenario.

Here is the machine info:
Linux elm3b158 2.6.16.43-0.5-ppc64 #1 SMP Mon Mar 19 08:28:24 UTC 2007 ppc64 ppc64 ppc64 GNU/Linux
SUSE Linux Enterprise Server 10 SP1 RC1 (ppc)



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