Re: [patch] Userland DTrace

On 08/02/2013 20:04, Matt Burke wrote:
> I've been spending some time trying to get the fasttrap provider to work
> on FreeBSD without panicing. I believe I have succeeded, at least to the
> point where it's no longer panicing.
>
> There were two panic causes. The first was
> http://www.freebsd.org/cgi/query-pr.cgi?pr=165541 - the FreeBSD port of
> fasttrap.c caused ftp_rcount to be left >0. To fix this I've got rid of
> the early return and reverted to the opensolaris way.
>
> A second panic then showed up intermittently when fasttrap_pid_cleanup_cb
> was run while something in userland had locks. Using sx_try_xlock calls
> has stopped the panics and shouldn't affect operation AFAICT.
>
> This is against r246454.
>
>
> Although this has fixed the panics for me, I'm finding a lot of stuff just
> isn't actually working, with dtrace and the traced process just chewing
> CPU. Truss on the dtrace shows a heck of a lot of ptrace() calls and I
> have no idea what the target is doing... CPU time is split 2:1
> dtrace:target
>
>
> Also noteworthy is the LOR on the first time you try to use the fasttrap
> provider: http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/165479
>
> The lock order there seems right, so I'm guessing "something else" must
> have done it wrong first? How can I find out what the "something else"
> is?

Hi Matt,
It might be worth posting the question to the dtrace list if your 
question is unanswered.
http://dtrace.org/blogs/mailing-list/

Regards,

Sevan