bug#29335: 'guix publish' workers occasionally crash

[ludo@gnu.org (Ludovic Courtès)]

ludo@gnu.org (Ludovic Courtès) skribis:

> On berlin I’ve noticed that the ‘guix publish’ workers would
> occasionally stop working: the main thread would keep replying to HTTP
> requests, but the worker threads would no longer do anything, and would
> leave behind them a bunch of .tmp files in /var/cache/guix/publish.
>
> I captured the output of ‘guix publish’ (guix-0.13.0-8.357ab93) and the
> only clue I have is this:
>
> GET /6kl9ydqmgklcqhxswg6v5isq5n1ih5gp.narinfo
> In guix/workers.scm:
>      74:9  2 (_)
>     78:32  1 (_ srfi-34 #<condition &nix-connection-error [file: "/v…>)
> In unknown file:
>            0 (make-stack #t)
> ERROR: In procedure make-stack:
> ERROR: Throw to key `srfi-34' with args `(#<condition &nix-connection-error [file: "/var/guix/daemon-socket/socket" errno: 9] 3ba2ea0>)'.
> GET /fgiih42mg2sr82mbmzf56grvrf021im6.narinfo

Good news, this is fixed in 85f4f7b79040d982c6a655c898b4cd00d868fa9c.

This could be reproduced by running ‘guix publish’ with 10 workers or
more, and then triggering nar compression en masse with ‘guix weather’.

EBADF was due to a race condition in zlib.scm when closing gzip output
ports:

          ;; 'gzclose' closes the underlying file descriptor.  'close-port'
          ;; calls close(2) and gets EBADF, which we swallow.
          (gzclose gzfile)
          (ignore-EBADF (close-port port)))

There was a window after the ‘gzclose’ call during which the file
descriptor for GZFILE and PORT above could be reused for something else,
and then ‘close-port’ would close it.

Thanks,
Ludo’.