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09 March 2009

kernel panic when calling printk() inside scheduler code...

An interesting question arose in kernelnewbies mailing list. Basically, somebody somebody asked why calling printk() when intercepting scheduler code (using jprobe) results in kernel panic. Full thread can be read here.

My analysis, somehow during module initialization, printk() must not be executed to avoid recursively waking up klogd. The original poster said it didn't help. Finally, he found a workaround, that is by incrementing a variable named oops_in_progress. I bet works like a flag. When it's greater than zero, it prevents klogd to wake up. Problem solved!

Note: klogd is a kernel thread that reads kernel ring buffer and send it to user space daemon syslogd if there's any entries there. Those are the messages that we see ending up in /var/log/messages (for non critical kernel messages).

regards,

Mulyadi.

1 comment:

iyepb0 said...

Ndak mudeng2 aku iki... :D