bug#27476: guix pull fails on powerful server

[ludo@gnu.org (Ludovic Courtès)]

Hi,

Andy Wingo <wingo@igalia.com> skribis:

> On Fri 22 Sep 2017 16:10, ludo@gnu.org (Ludovic Courtès) writes:
>
>> Hi Ricardo,
>>
>> Ricardo Wurmus <rekado@elephly.net> skribis:
>>
>>> The following derivation will be built:
>>>    /gnu/store/yvyfkns3w3vm7ynwbr7mvxcmin4gd2a0-guix-latest.drv
>>> copying and compiling to '/gnu/store/7m52dkr98nhwgpsx20mmpwyw2yzj58d3-guix-latest' with Guile 2.2.2...
>>> loading...       25.4% of 629 filesrandom seed for tests: 1506066913
>>> loading...       99.8% of 629 files
>>> compiling...     69.2% of 629 filesice-9/threads.scm:289:22: In procedure loop:
>>> ice-9/threads.scm:289:22: Syntax error:
>>> guix/scripts.scm:130:2: >>=: >>= (bind) used outside of 'with-monad' in form (>>= (apply set-build-options* #:use-substitutes
>>> ptions)) (lambda (unused-value) (mbegin %store-monad (mlet %store-monad ((derivation (origin->derivation (package-source pack
>>> tutes? use-substitutes? #:dry-run? dry-run?) (return (show-derivation-outputs derivation)))))))
>>
>> This was reported at <https://bugs.gnu.org/27476>, and I suspect a
>> thread-safety issue.  However, syntax parameters are purely functional
>> AFAICS, so I fail to see why multithreading could be a problem.
>>
>> Andy, any idea what could be causing this?
>
> I have heard of but not seen a number of similar bugs: errors that
> "can't happen" but which appear under multiple threads.  I don't know
> what underlying pattern is.  Has anyone found a test case that reliably
> reproduces?

With this program:

--8<---------------cut here---------------start------------->8---
(use-modules (ice-9 threads)
             (srfi srfi-1))

(define-syntax-parameter foo
  (identifier-syntax +))

(define threads
  (unfold (lambda (x) (> x 100))
          (lambda (x)
            (call-with-new-thread
             (lambda ()
               (while #t
                 (macroexpand
                  '(syntax-parameterize ((foo (identifier-syntax -)))
                     (foo y z)))))))
          1+
          0))

(for-each join-thread threads)
--8<---------------cut here---------------end--------------->8---

I managed to get a segfault:

--8<---------------cut here---------------start------------->8---
$ guile syntax-parms.scm
;;; note: source file /home/ludo/src/guix/syntax-parms.scm
;;;       newer than compiled /home/ludo/.cache/guile/ccache/2.2-LE-8-3.A/home/ludo/src/guix/syntax-parms.scm.go
;;; note: auto-compilation is enabled, set GUILE_AUTO_COMPILE=0
;;;       or pass the --no-auto-compile argument to disable.
;;; compiling /home/ludo/src/guix/syntax-parms.scm
;;; compiled /home/ludo/.cache/guile/ccache/2.2-LE-8-3.A/home/ludo/src/guix/syntax-parms.scm.go
In /home/ludo/src/guix/syntax-parms.scm:
    13:17 13 (_)
In ice-9/psyntax.scm:
  1233:22 12 (expand-top-sequence (#(ribcage #(x) #((m-1dff1b83541ce327-7f97c #)) #) # …) …)
In ice-9/boot-9.scm:
   230:17 11 (map1 (#<tree-il (lambda-case (((id) #f #f #f () (id-1dff1b83541ce327-7fb4…>))
In ice-9/psyntax.scm:
  2053:19 10 (_ _ #() (foo y z) ())
In ice-9/boot-9.scm:
   230:17  9 (map1 #())
In ice-9/psyntax.scm:
  1408:12  8 (_ _)
  1788:11  7 (lp (1) (11 0 . 0))
  1678:45  6 (parse _ _ _ _ _ _ _)
In ice-9/boot-9.scm:
   230:17  5 (map1 ((tmp-1dff1b83541ce327-7f98b 0 . 0)))
In ice-9/psyntax.scm:
  2701:67  4 Adres-eraro
--8<---------------cut here---------------end--------------->8---

… but then I failed to reproduce it again (that was on my 4-thread
laptop).

Ludo’.