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RE: reentrant probes
- From: "Seth, Rohit" <rohit dot seth at intel dot com>
- To: "Frank Ch. Eigler" <fche at redhat dot com>
- Cc: <systemtap at sources dot redhat dot com>
- Date: Mon, 2 May 2005 10:43:10 -0700
- Subject: RE: reentrant probes
Frank Ch. Eigler <mailto:fche@redhat.com> wrote on Monday, May 02, 2005
10:33 AM:
> Hi -
>
> rohit.seth wrote:
>
>> [...] I think it will be quite useful to allow renentrancy in
>> probes. Not sure why would you want to restrict this. [...]
>
> It seems hazardous, for example by permitting infinite regress, should
> a breakpoint be placed into the normal execution path of the kprobes
> layer itself. It would also require supporting nested int3 faults,
> definitely requiring extra stack space.
>
You will in all probability need to support a nested int3 faults (and
yes that increases the pressure on limited stack space further). For
example, a scenario like where a probe handler is executing and then
gets an interrupt and as part of handling that interrupt, the execution
hits another probe....
> Maybe these are surmountable by some combination of run-time nesting
> limits (like the ones we'd have in translated recursive scripts), and
> blacklisting some modules (e.g. kprobes itself) from becoming
> systemtap probing targets.
>
I agree some static time sanity check (to find infinte regress) will be
useful.
-rohit