[PATCH,Hurd] Fix hang on fork

[Samuel Thibault]

If e.g. a signal is being received while we are running fork(), the signal
thread may be having our SS lock when we make the space copy, and thus in the
child we can not take the SS lock any more.

* sysdeps/mach/hurd/fork.c (__fork): Lock SS->lock around __proc_dostop() call.

Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>

---
 sysdeps/mach/hurd/fork.c | 4 ++++
 1 file changed, 4 insertions(+)

--- a/sysdeps/mach/hurd/fork.c
+++ b/sysdeps/mach/hurd/fork.c
@@ -130,9 +130,13 @@ __fork (void)
       ports_locked = 1;
 
 
+      /* Keep our SS locked while stopping other threads, so they don't get a
+       * chance to be having it locked in the copied space.  */
+      __spin_lock(&ss->lock);
       /* Stop all other threads while copying the address space,
         so nothing changes.  */
       err = __proc_dostop (_hurd_ports[INIT_PORT_PROC].port, ss->thread);
+      __spin_unlock(&ss->lock);
       if (!err)
        {
          stopped = 1;