Re: Memory corruption after fork, only on AMD CPUs

[Michael Pratt <mpratt%google.com@localhost>]

[This is a reply to
https://mail-index.netbsd.org/tech-kern/2021/12/01/msg027830.html. I
just joined the mailing list and can't seem to find the metadata
required for a proper reply. Apologies.]

I filed https://gnats.netbsd.org/56535 for this a while ago, which has
an even simpler reproducer: a direct fork() call with a child that
immediately exits sometimes causes memory corruption in the parent
process.

We've kept looking since filing https://gnats.netbsd.org/56535 but
haven't had luck on further simplification. No C reproducer yet,
unfortunately. (No crashes if the Go parent process is single-threaded
either.)

This feels like a bug in memory management somewhere (TLB invalidation
issue, bug in copy-on-write?). Fundamentally, we have the parent
process getting corrupt memory after calling fork with an
(effectively) no-op child. That just shouldn't happen.

I think we need someone familiar with NetBSD memory management
internals to help take a look. Otherwise I'm afraid we won't figure it
out and will have to declare that Go doesn't work on NetBSD on AMD
CPUs.

gdt: that does sound like a different issue to me. It may be worth
filing a bug at https://github.com/golang/go/issues with the crash
details.

Thanks,
Michael