bug#27144: guix publish: “mutex already locked by thread”

[Ludovic Courtès]

Seen on hydra.gnu.org:

--8<---------------cut here---------------start------------->8---
GET /jkpcipgxfyfb60pr4b5n4x4j9k5mcxpp.narinfo
In ice-9/boot-9.scm:
 160: 5 [catch #t #<catch-closure 2581c20> ...]
In unknown file:
   ?: 4 [apply-smob/1 #<catch-closure 2581c20>]
In guix/workers.scm:
  84: 3 [#<procedure 2545600 at guix/workers.scm:82:2 ()>]
  72: 2 [loop]
  76: 1 [#<procedure 24a8620 at guix/workers.scm:73:11 (key . args)> misc-error 
...]
In unknown file:
   ?: 0 [make-stack #t]
ERROR: In procedure make-stack:
ERROR: Throw to key `misc-error' with args `("mutex already locked by thread")'.
--8<---------------cut here---------------end--------------->8---

This is with
/gnu/store/cxmj38x6rh0ykq3d5dlqbxr5h1zgiiaf-guile2.0-guix-0.13.0-1.a6d728b.

Ludo'.