In what I’ve read about the bug, there is no requirement that two virtual cores be running OCaml code (or rather, the malfunctioning instruction sequence). Is that accurate? If so, it shouldn’t matter whether the OCaml code is parallelized or not.
As far as I know, the users reporting in Lwt were not running Lwt or OCaml in parallel.
On Fri, 30 Jun 2017, Gabriel Scherer wrote:Here is my list of affected OCaml projects known so far (it seems
surprisingly less rare than I thought at first):
- an (unnamed) industrial user noticed the issue in Spring 2016, as
reported by Xavier on the bugtracker:
https://caml.inria.fr/mantis/view.php?id=7452#c17109
- ahrefs noticed issues in late 2016, as reported by Joris
Giovannangeli on the bugtracker issue or his longer piece
https://tech.ahrefs.com/skylake-bug-a-detective-story-ab1ad2beddcd
- Lwt users were also affected (first report from Sebastien Mondet in
February 2017):
https://github.com/ocsigen/lwt/issues/315
- Julia Lawall reported segfaults from a downstream user on the caml-list,
that seem extreley likely to be related to this issue (they
disappear with hyperthreading disabled)
https://sympa.inria.fr/sympa/arc/caml-list/2017-06/msg00115.html
At this point it seems reasonable to assume that any
computation-intensive OCaml program that is run in parallel may be
affected.
The Coccinelle code is compiled with Parmap, but I don't think that Parmapis invoked in the failing execution. I could check on this.julia
On Fri, Jun 30, 2017 at 10:15 AM, Xavier Leroy <xavier.leroy@inria.fr> wrote:
Clarification:
Possible fixes include:
- Apply the microcode update recently released by Intel [...]
Contradicting what I wrote before, microcode updates are available both for Skylake and for Kaby Lake processors. It's only how to apply those updates that differs slightly between Skylake and Kaby Lake. Again, see the excellent instructions at
https://lists.debian.org/debian-devel/2017/06/msg00308.html
Sorry for the confusion.
- Xavier Leroy
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