[Bug testsuite/31312] attach-many-short-lived-threads gives inconsistent results

["tromey at sourceware dot org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=31312

--- Comment #14 from Tom Tromey <tromey at sourceware dot org> ---
(In reply to Carl E Love from comment #13)
> There are some timing
> issues that can cause the kernel to legitimately return EPERM.  He pointed
> me to the ptrace Linux man page

Ugh :}  Disappointing but what can we really do about it, I suppose.
I guess if the race happens more for you, all we can conclude is
that Power 10 is just too darn fast.

 Another possible cause for the EPERM is if
> ptrace is already connected to the process.  I tried to determine if this
> was in fact the case.  Specifically if the detach hadn't completed yet but
> was not able to show that was the failure case.  

Yeah, I was wondering about this as a theory for why subsequent
attempts all fail.  I probably distracted us a bit by ranting but
IIUC this part still isn't understood.  Could you maybe verify
that gdb thinks it has detached all the threads it attached to?
If so and the bug persists, I think we can just write it off
as another kernel bug.

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