iwlwifi: fix double free/complete in firmware loading

Linus reported that due to mac80211 failing to register
the device (due to WoWLAN) his machine crashed etc. as
we double-freed the vmalloc() firmware area. His patch
to fix it was very similar to this one but I noticed
that there's another bug in the area: we complete the
completion before starting, so since we're running in
a work struct context stop() could be called while in
the middle of start() which will almost certainly lead
to issues.

Make a modification similar to his to avoid the double-
free but also move the completion to another spot so it
is only done after start() either finished or failed so
that stop() can have a consistent state.
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/iwlwifi/iwl-drv.c

@@ -861,13 +861,18 @@ static void iwl_ucode_callback(const struct firmware *ucode_raw, void *context)
 
 	/* We have our copies now, allow OS release its copies */
 	release_firmware(ucode_raw);
-	complete(&drv->request_firmware_complete);
 
 	drv->op_mode = iwl_dvm_ops.start(drv->trans, drv->cfg, &drv->fw);
 
 	if (!drv->op_mode)
-		goto out_free_fw;
+		goto out_unbind;
 
+	/*
+	 * Complete the firmware request last so that
+	 * a driver unbind (stop) doesn't run while we
+	 * are doing the start() above.
+	 */
+	complete(&drv->request_firmware_complete);
 	return;
 
  try_again: