X wcfs: _fuse_unmount: Try first `kill -TERM` before `kill -QUIT` wcfs

Just aborting the FUSE connection does not make WCFS to exit. This abort
is needed to avoid deadlocks, but we should also signal WCFS it should
stop. Not doing so will lead to timeout in wait after FUSE connection
abort and `kill -QUIT` triggered, which makes WCFS crash and print lots
of traceback to stderr before exiting.

wcfs/__init__.py

@@ -71,7 +71,7 @@ import logging as log
 from os.path import dirname
 from stat import S_ISDIR
 from errno import ENOENT, ENOTCONN, EEXIST
-from signal import SIGQUIT, SIGKILL
+from signal import SIGTERM, SIGQUIT, SIGKILL
 
 from golang import chan, select, default, func, defer
 from golang import context, errors, sync, time
@@ -423,41 +423,43 @@ def __stop(wcsrv, ctx, _onstuck):
         if _procwait_(timeoutFrac(0.5), wcsrv._proc):
             return
 
-        log.warn("\nC: wcfs.go does not exit")
-        log.warn("-> kill -QUIT wcfs.go ...\n")
+        log.warn("wcfs.go does not exit (after SIGTERM)")
+        log.warn("-> kill -QUIT wcfs.go ...")
         os.kill(wcsrv._proc.pid, SIGQUIT)
 
         if _procwait_(timeoutFrac(0.25), wcsrv._proc):
             return
-        log.warn("\nC: wcfs.go does not exit (after SIGQUIT)")
-        log.warn("-> kill -KILL wcfs.go ...\n")
+        log.warn("wcfs.go does not exit (after SIGQUIT)")
+        log.warn("-> kill -KILL wcfs.go ...")
         os.kill(wcsrv._proc.pid, SIGKILL)
 
         if _procwait_(timeoutFrac(0.25), wcsrv._proc):
             return
-        log.warn("\nC: wcfs.go does not exit (after SIGKILL; probably it is stuck in kernel)")
-        log.warn("-> nothing we can do...\n")  # XXX dump /proc/pid/task/*/stack instead  (ignore EPERM)
+        log.warn("wcfs.go does not exit (after SIGKILL; probably it is stuck in kernel)")
+        log.warn("-> nothing we can do...")  # XXX dump /proc/pid/task/*/stack instead  (ignore EPERM)
         if _onstuck is not None:
             _onstuck()
         else:
             _procwait(context.background(), wcsrv._proc)
     defer(_)
 
-    @func
-    def _():
     try:
         if _is_mountpoint(wcsrv.mountpoint): # could be unmounted from outside
             _fuse_unmount(wcsrv.mountpoint)
     except:
-            # if clean unmount failed -> force abort of fuse connection
+        # if clean unmount failed -> kill -TERM wcfs and force abort of fuse connection.
+        #
+        # aborting fuse connection is needed in case wcfs/kernel will be stuck
+        # in a deadlock even after being `kill -9`. See comments in tWCFS for details.
         def _():
+            log.warn("-> kill -TERM wcfs.go ...")
+            os.kill(wcsrv._proc.pid, SIGTERM)
             if wcsrv._fuseabort is not None:
-                    log.warn("aborting FUSE connection ...")
+                log.warn("-> aborting FUSE connection ...")
                 wcsrv._fuseabort.write(b"1\n")
                 wcsrv._fuseabort.flush()
         defer(_)
         raise
-    defer(_)
 
 
 # ---- misc ----