* dcrt0.cc (child_info_fork::alloc_stack_hard_way): Change sense of guard test.

Increase size of stack reserved and increase size before the current stack
pointer.  Use pointers when doing arithmetic.
(dll_crt0_1): Initialize exception handler when we notice we're the child of a
fork from non-main thread.
* fork.cc (frok::parent): Make argument volatile.
(frok::child): Ditto.
(lock_signals): New class.
(lock_pthread): Ditto.
(hold_everhthing): Ditto.
(frok::parent): Move atforkprepare and atforkparent to lock_pthread class.
(fork): Make ischild boolean.  Use hold_everything variable within limited
scope to set various mutexes in such a way as to avoid deadlocks.
* thread.h (pthread_mutex::tid): New variable, active when debugging for
tracking thread id of owner.
(pthread_mutex::set_owner): Set tid when debugging.
* thread.cc (pthread_mutex::pthread_mutex): Clear tid.
(pthread_mutex::_unlock): Ditto when unlocking.
(pthread_mutex::fixup_after_fork): Set tid to special value after forking since
owner is unknown.

1 files changed, 100 insertions, 30 deletions

diff --git a/winsup/cygwin/fork.cc b/winsup/cygwin/fork.cc
index 51afce9c1..f7949d36d 100644
--- a/winsup/cygwin/fork.cc
+++ b/winsup/cygwin/fork.cc
@@ -45,11 +45,87 @@ class frok
   const char *error;
   int child_pid;
   int this_errno;
-  int __stdcall parent (void *esp);
-  int __stdcall child (void *esp);
+  int __stdcall parent (volatile char * volatile here);
+  int __stdcall child (volatile char * volatile here);
   friend int fork ();
 };
 
+class lock_signals
+{
+  bool worked;
+public:
+  lock_signals ()
+  {
+    worked = sig_send (NULL, __SIGHOLD) == 0;
+  }
+  operator int () const
+  {
+    return worked;
+  }
+  void dont_bother ()
+  {
+    worked = false;
+  }
+  ~lock_signals ()
+  {
+    if (worked)
+      sig_send (NULL, __SIGNOHOLD);
+  }
+};
+
+class lock_pthread
+{
+  bool bother;
+public:
+  lock_pthread (): bother (1)
+  {
+    pthread::atforkprepare ();
+  }
+  void dont_bother ()
+  {
+    bother = false;
+  }
+  ~lock_pthread ()
+  {
+    if (bother)
+      pthread::atforkparent ();
+  }
+};
+
+class hold_everything
+{
+  bool& ischild;
+  /* Note the order of the locks below.  It is important,
+     to avoid races, that the lock order be preserved.
+     
+     pthread is first because it serves as a master lock
+     against other forks being attempted while this one is active.
+     
+     signals is next to stop signal processing for the duration
+     of the fork.
+
+     process is last.  If it is put before signals, then a deadlock
+     could be introduced if the process attempts to exit due to a signal. */
+  lock_pthread pthread;
+  lock_signals signals;
+  lock_process process;
+
+public:
+  hold_everything (bool& x): ischild (x) {}
+  operator int () const {return signals;}
+
+  ~hold_everything()
+  {
+    if (ischild)
+      {
+	pthread.dont_bother ();
+	process.dont_bother ();
+	signals.dont_bother ();
+      }
+  }
+
+};
+
 static void
 resume_child (HANDLE forker_finished)
 {
@@ -92,7 +168,7 @@ sync_with_parent (const char *s, bool hang_self)
 }
 
 int __stdcall
-frok::child (void *)
+frok::child (volatile char * volatile here)
 {
   HANDLE& hParent = ch.parent;
   extern void fixup_hooks_after_fork ();
@@ -213,7 +289,7 @@ slow_pid_reuse (HANDLE h)
 #endif
 
 int __stdcall
-frok::parent (void *stack_here)
+frok::parent (volatile char * volatile stack_here)
 {
   HANDLE forker_finished;
   DWORD rc;
@@ -224,8 +300,6 @@ frok::parent (void *stack_here)
   pinfo child;
   static char errbuf[256];
 
-  pthread::atforkprepare ();
-
   int c_flags = GetPriorityClass (hMainProc);
   debug_printf ("priority class %d", c_flags);
 
@@ -271,7 +345,7 @@ frok::parent (void *stack_here)
   ch.forker_finished = forker_finished;
 
   ch.stackbottom = _tlsbase;
-  ch.stacktop = stack_here;
+  ch.stacktop = (void *) stack_here;
   ch.stacksize = (char *) ch.stackbottom - (char *) stack_here;
   debug_printf ("stack - bottom %p, top %p, size %d",
 		ch.stackbottom, ch.stacktop, ch.stacksize);
@@ -492,7 +566,6 @@ frok::parent (void *stack_here)
 
   ForceCloseHandle (forker_finished);
   forker_finished = NULL;
-  pthread::atforkparent ();
 
   return child_pid;
 
@@ -516,14 +589,13 @@ extern "C" int
 fork ()
 {
   frok grouped;
-  MALLOC_CHECK;
 
   debug_printf ("entering");
   grouped.first_dll = NULL;
   grouped.load_dlls = 0;
 
   int res;
-  int ischild;
+  bool ischild = false;
 
   myself->set_has_pgid_children ();
 
@@ -535,30 +607,28 @@ fork ()
       return -1;
     }
 
-  lock_process now;
-  if (sig_send (NULL, __SIGHOLD))
-    {
-      if (exit_state)
-	Sleep (INFINITE);
-      set_errno (EAGAIN);
-      return -1;
-    }
+  {
+    hold_everything held_everything (ischild);
 
-  ischild = setjmp (grouped.ch.jmp);
+    if (!held_everything)
+      {
+	if (exit_state)
+	  Sleep (INFINITE);
+	set_errno (EAGAIN);
+	return -1;
+      }
 
-  void *esp;
-  __asm__ volatile ("movl %%esp,%0": "=r" (esp));
+    ischild = !!setjmp (grouped.ch.jmp);
 
-  if (ischild)
-    {
-      res = grouped.child (esp);
-      now.dont_bother ();
-    }
-  else
-    {
+    volatile char * volatile esp;
+    __asm__ volatile ("movl %%esp,%0": "=r" (esp));
+
+
+    if (!ischild)
       res = grouped.parent (esp);
-      sig_send (NULL, __SIGNOHOLD);
-    }
+    else
+      res = grouped.child (esp);
+  }
 
   MALLOC_CHECK;
   if (ischild || res > 0)