2007-07-08  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* linux-nat.c (linux_lwp_is_zombie): New function.
	(wait_lwp): Fix lockup on exit of the thread group leader.
	(linux_xfer_partial): Renamed to ...
	(linux_xfer_partial_lwp): ... here.
	(linux_xfer_partial): New function wrapping LINUX_XFER_PARTIAL_LWP.

--- ./gdb/linux-nat.c	3 Jul 2007 17:01:55 -0000	1.65
+++ ./gdb/linux-nat.c	7 Jul 2007 15:21:57 -0000
@@ -1343,6 +1343,31 @@ linux_handle_extended_wait (struct lwp_i
 		  _("unknown ptrace event %d"), event);
 }
 
+static int
+linux_lwp_is_zombie (long lwp)
+{
+  char buffer[MAXPATHLEN];
+  FILE *procfile;
+  int retval = 0;
+
+  sprintf (buffer, "/proc/%ld/status", lwp);
+  procfile = fopen (buffer, "r");
+  if (procfile == NULL)
+    {
+      warning (_("unable to open /proc file '%s'"), buffer);
+      return 0;
+    }
+  while (fgets (buffer, sizeof (buffer), procfile) != NULL)
+    if (strcmp (buffer, "State:\tZ (zombie)\n") == 0)
+      {
+	retval = 1;
+	break;
+      }
+  fclose (procfile);
+
+  return retval;
+}
+
 /* Wait for LP to stop.  Returns the wait status, or 0 if the LWP has
    exited.  */
 
@@ -1350,16 +1375,31 @@ static int
 wait_lwp (struct lwp_info *lp)
 {
   pid_t pid;
-  int status;
+  int status = 0;
   int thread_dead = 0;
 
   gdb_assert (!lp->stopped);
   gdb_assert (lp->status == 0);
 
-  pid = my_waitpid (GET_LWP (lp->ptid), &status, 0);
-  if (pid == -1 && errno == ECHILD)
+  /* Thread group leader may have exited but we would lock up by WAITPID as it
+     waits on all its threads; __WCLONE is not applicable for the leader.
+     The thread leader restrictions is only a performance optimization here.
+     LINUX_NAT_THREAD_ALIVE cannot be used here as it requires a STOPPED
+     process; it gets ESRCH both for the zombie and for running processes.  */
+  if (is_lwp (lp->ptid) && GET_PID (lp->ptid) == GET_LWP (lp->ptid)
+      && linux_lwp_is_zombie (GET_LWP (lp->ptid)))
+    {
+      thread_dead = 1;
+      if (debug_linux_nat)
+	fprintf_unfiltered (gdb_stdlog, "WL: Threads leader %s vanished.\n",
+			    target_pid_to_str (lp->ptid));
+    }
+
+  if (!thread_dead)
     {
-      pid = my_waitpid (GET_LWP (lp->ptid), &status, __WCLONE);
+      pid = my_waitpid (GET_LWP (lp->ptid), &status, 0);
+      if (pid == -1 && errno == ECHILD)
+	pid = my_waitpid (GET_LWP (lp->ptid), &status, __WCLONE);
       if (pid == -1 && errno == ECHILD)
 	{
 	  /* The thread has previously exited.  We need to delete it
@@ -3144,10 +3159,12 @@ linux_proc_pending_signals (int pid, sig
   fclose (procfile);
 }
 
+/* Transfer from the specific LWP currently set by PID of INFERIOR_PTID.  */
+
 static LONGEST
-linux_xfer_partial (struct target_ops *ops, enum target_object object,
-                    const char *annex, gdb_byte *readbuf,
-		    const gdb_byte *writebuf, ULONGEST offset, LONGEST len)
+linux_xfer_partial_lwp (struct target_ops *ops, enum target_object object,
+			const char *annex, gdb_byte *readbuf,
+			const gdb_byte *writebuf, ULONGEST offset, LONGEST len)
 {
   LONGEST xfer;
 
@@ -3164,6 +3181,45 @@ linux_xfer_partial (struct target_ops *o
 			     offset, len);
 }
 
+/* nptl_db expects being able to transfer memory just by specifying PID.
+   After the thread group leader exists the Linux kernel turns the task
+   into zombie no longer permitting accesses to its memory.
+   Transfer the memory from an arbitrary LWP_LIST entry in such case.  */
+
+static LONGEST
+linux_xfer_partial (struct target_ops *ops, enum target_object object,
+                    const char *annex, gdb_byte *readbuf,
+		    const gdb_byte *writebuf, ULONGEST offset, LONGEST len)
+{
+  LONGEST xfer;
+  struct lwp_info *lp;
+  /* Not using SAVE_INFERIOR_PTID already here for better performance.  */
+  struct cleanup *old_chain = NULL;
+  ptid_t inferior_ptid_orig = inferior_ptid;
+
+  errno = 0;
+  xfer = linux_xfer_partial_lwp (ops, object, annex, readbuf, writebuf,
+				 offset, len);
+
+  for (lp = lwp_list; xfer == 0 && (errno == EACCES || errno == ESRCH)
+		      && lp != NULL; lp = lp->next)
+    {
+      if (!is_lwp (lp->ptid) || ptid_equal (lp->ptid, inferior_ptid_orig))
+        continue;
+      
+      if (old_chain == NULL)
+	old_chain = save_inferior_ptid ();
+      inferior_ptid = BUILD_LWP (GET_LWP (lp->ptid), GET_LWP (lp->ptid));
+      errno = 0;
+      xfer = linux_xfer_partial_lwp (ops, object, annex, readbuf, writebuf,
+				     offset, len);
+    }
+
+  if (old_chain != NULL)
+    do_cleanups (old_chain);
+  return xfer;
+}
+
 /* Create a prototype generic Linux target.  The client can override
    it with local methods.  */