gnu: guile-ssh: Close RREPL channel ports before they are finalized.

Partly fixes <https://bugs.gnu.org/26976>.

* gnu/packages/patches/guile-ssh-channel-finalization.patch: New file.
* gnu/packages/ssh.scm (guile-ssh)[source](patches): Use it.
* gnu/local.mk (dist_patch_DATA): Add it.

gnu/local.mk

@@ -656,8 +656,9 @@ dist_patch_DATA =						\
   %D%/packages/patches/guile-present-coding.patch		\
   %D%/packages/patches/guile-relocatable.patch			\
   %D%/packages/patches/guile-rsvg-pkgconfig.patch		\
-  %D%/packages/patches/guile-ssh-rexec-bug.patch		\
+  gnu/packages/patches/guile-ssh-channel-finalization.patch	\
   %D%/packages/patches/guile-ssh-double-free.patch		\
+  %D%/packages/patches/guile-ssh-rexec-bug.patch		\
   %D%/packages/patches/gtk2-respect-GUIX_GTK2_PATH.patch	\
   %D%/packages/patches/gtk2-respect-GUIX_GTK2_IM_MODULE_FILE.patch \
   %D%/packages/patches/gtk2-theme-paths.patch			\

gnu/packages/patches/guile-ssh-channel-finalization.patch

@@ -0,0 +1,28 @@
+Avoid asynchronous channel finalization, which could lead to segfaults due to
+libssh not being thread-safe: <https://bugs.gnu.org/26976>.
+
+--- guile-ssh-0.11.0/modules/ssh/dist/node.scm	2017-06-13 14:37:44.861671297 +0200
++++ guile-ssh-0.11.0/modules/ssh/dist/node.scm	2017-06-13 14:38:02.841580565 +0200
+@@ -391,11 +391,18 @@ listens on an expected port, return #f o
+   "Evaluate QUOTED-EXP on the node and return the evaluated result."
+   (let ((repl-channel (node-open-rrepl node)))
+     (rrepl-skip-to-prompt repl-channel)
+-    (call-with-values (lambda () (rrepl-eval repl-channel quoted-exp))
+-      (lambda vals
+-        (and (node-stop-repl-server? node)
++    (dynamic-wind
++      (const #t)
++      (lambda ()
++        (rrepl-eval repl-channel quoted-exp))
++      (lambda ()
++        (when (node-stop-repl-server? node)
+              (node-stop-server node))
+-        (apply values vals)))))
++
++        ;; Close REPL-CHANNEL right away to prevent finalization from
++        ;; happening in another thread at the wrong time (see
++        ;; <https://bugs.gnu.org/26976>.)
++        (close-port repl-channel)))))
+ 
+ (define (node-eval-1 node quoted-exp)
+   "Evaluate QUOTED-EXP on the node and return the evaluated result.  The

gnu/packages/ssh.scm

@@ -229,7 +229,8 @@ Additionally, various channel-specific options can be negotiated.")
                (base32
                 "0r261i8kc3avbmbwgyzak2vnqwssjlgz37g2y2fwm80w9bmn2m7j"))
               (patches (search-patches "guile-ssh-rexec-bug.patch"
-                                       "guile-ssh-double-free.patch"))
+                                       "guile-ssh-double-free.patch"
+                                       "guile-ssh-channel-finalization.patch"))
               (modules '((guix build utils)))
               (snippet
                ;; 'configure.ac' mistakenly tries to link files from examples/