kobject: provide more diagnostic info for kobject_add_internal() failures

1/ convert open-coded KERN_ERR+dump_stack() to WARN(), so that automated
   tools pick up this warning.

2/ include the 'child' and 'parent' kobject names.  This information was
   useful for tracking down the case where scsi invoked device_del() on a
   parent object and subsequently invoked device_add() on a child.  Now the
   warning looks like:

     kobject_add_internal failed for target8:0:16 (error: -2 parent: end_device-8:0:24)
     Pid: 2942, comm: scsi_scan_8 Not tainted 3.3.0-rc7-isci+ #2
     Call Trace:
      [<ffffffff8125e551>] kobject_add_internal+0x1c1/0x1f3
      [<ffffffff81075149>] ? trace_hardirqs_on+0xd/0xf
      [<ffffffff8125e659>] kobject_add_varg+0x41/0x50
      [<ffffffff8125e723>] kobject_add+0x64/0x66
      [<ffffffff8131124b>] device_add+0x12d/0x63a
      [<ffffffff8125e0ef>] ? kobject_put+0x4c/0x50
      [<ffffffff8132f370>] scsi_sysfs_add_sdev+0x4e/0x28a
      [<ffffffff8132dce3>] do_scan_async+0x9c/0x145

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: James Bottomley <JBottomley@parallels.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

lib/kobject.c

@@ -192,14 +192,14 @@ static int kobject_add_internal(struct kobject *kobj)
 
 		/* be noisy on error issues */
 		if (error == -EEXIST)
-			printk(KERN_ERR "%s failed for %s with "
+			WARN(1, "%s failed for %s with "
 			     "-EEXIST, don't try to register things with "
 			     "the same name in the same directory.\n",
 			     __func__, kobject_name(kobj));
 		else
-			printk(KERN_ERR "%s failed for %s (%d)\n",
-			       __func__, kobject_name(kobj), error);
-		dump_stack();
+			WARN(1, "%s failed for %s (error: %d parent: %s)\n",
+			     __func__, kobject_name(kobj), error,
+			     parent ? kobject_name(parent) : "'none'");
 	} else
 		kobj->state_in_sysfs = 1;