registration error (rc -84) and -DSTP_OVERLOAD_THRESHOLD

[Frank Ch. Eigler]

mglt.biz wrote:

> [...]  While running my tap script, I receive WARNINGs and would
> like to knwo how to consider them. [...]

> WARNING: probe
> kernel.function("tcp_new_space@net/ipv4/tcp_input.c:4885") (address
> 0xffffffff814064f0) registration error (rc -84)

This is an error (-EILSEQ) that comes from the kernel, most likely
arch/x86/kernel/kprobes.c.  It may be a somehow blacklisted function,
or perhaps a problem with the 'optimized kprobes' widget.  It may help
to get a vmlinux disassembly around that 0xffffffff814064f0 address.


> How does it really impact the probe? For exmaple, does a probe on
> tcp_new_space for example don't consider the function ?

That's correct, such a probe will just not be activated, and its
handler never run.


> By the way, I also noticed some problems with the
> -DSTP_OVERLOAD_THRESHOLD. The script does not run and sometime it
> may result by frezzing the OS. We don't have any problems with the
> -DSTP_NO_OVERLOAD option for example. [...]

We'd probably need some more details.  Mis-set THRESHOLD type values
should do no worse than abort the script prematurely.  Try 
   # stap -t -v
Share the script and its invocation.

- FChE