gdb/linux-nat: remove check based on current_inferior in linux_handle_extended_wait

The check removed by this patch, using current_inferior, looks wrong.
When debugging multiple inferiors with the Linux native target and
linux_handle_extended_wait is called, there's no guarantee about which
is the current inferior.  The vfork-done event we receive could be for
any inferior.  If the vfork-done event is for a non-current inferior, we
end up wrongfully ignoring it.  As a result, the core never processes a
TARGET_WAITKIND_VFORK_DONE event, program_space::breakpoints_not_allowed
is never cleared, and breakpoints are never reinserted.  However,
because the Linux native target decided to ignore the event, it resumed
the thread - while breakpoints out.  And that's bad.

The proposed fix is to remove this check.  Always report vfork-done
events and let infrun's logic decide if it should be ignored.  We don't
save much cycles by filtering the event here.

Add a test that replicates the situation described above.  See comments
in the test for more details.

Change-Id: Ibe33c1716c3602e847be6c2093120696f2286fbf

1 files changed, 4 insertions, 13 deletions

diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
index a9b093c..dff8d07 100644
--- a/gdb/linux-nat.c
+++ b/gdb/linux-nat.c
@@ -1990,20 +1990,11 @@ linux_handle_extended_wait (struct lwp_info *lp, int status)
 
   if (event == PTRACE_EVENT_VFORK_DONE)
     {
-      if (current_inferior ()->waiting_for_vfork_done)
-	{
-	  linux_nat_debug_printf
-	    ("Got expected PTRACE_EVENT_VFORK_DONE from LWP %ld: stopping",
-	     lp->ptid.lwp ());
-
-	  ourstatus->set_vfork_done ();
-	  return 0;
-	}
-
       linux_nat_debug_printf
-	("Got PTRACE_EVENT_VFORK_DONE from LWP %ld: ignoring", lp->ptid.lwp ());
-
-      return 1;
+	("Got PTRACE_EVENT_VFORK_DONE from LWP %ld",
+	 lp->ptid.lwp ());
+	ourstatus->set_vfork_done ();
+	return 0;
     }
 
   internal_error (__FILE__, __LINE__,