iwlwifi: pcie: WARN upon traffic while flushing TX queues

This must not happen - otherwise we might keep flushing
forever.
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>

drivers/net/wireless/iwlwifi/pcie/trans.c

@@ -1270,6 +1270,8 @@ static int iwl_trans_pcie_wait_txq_empty(struct iwl_trans *trans, u32 txq_bm)
 
 	/* waiting for all the tx frames complete might take a while */
 	for (cnt = 0; cnt < trans->cfg->base_params->num_of_queues; cnt++) {
+		u8 wr_ptr;
+
 		if (cnt == trans_pcie->cmd_queue)
 			continue;
 		if (!test_bit(cnt, trans_pcie->queue_used))
@@ -1278,9 +1280,19 @@ static int iwl_trans_pcie_wait_txq_empty(struct iwl_trans *trans, u32 txq_bm)
 			continue;
 		txq = &trans_pcie->txq[cnt];
 		q = &txq->q;
-		while (q->read_ptr != q->write_ptr && !time_after(jiffies,
-		       now + msecs_to_jiffies(IWL_FLUSH_WAIT_MS)))
+		wr_ptr = ACCESS_ONCE(q->write_ptr);
+
+		while (q->read_ptr != ACCESS_ONCE(q->write_ptr) &&
+		       !time_after(jiffies,
+				   now + msecs_to_jiffies(IWL_FLUSH_WAIT_MS))) {
+			u8 write_ptr = ACCESS_ONCE(q->write_ptr);
+
+			if (WARN_ONCE(wr_ptr != write_ptr,
+				      "WR pointer moved while flushing %d -> %d\n",
+				      wr_ptr, write_ptr))
+				return -ETIMEDOUT;
 			msleep(1);
+		}
 
 		if (q->read_ptr != q->write_ptr) {
 			IWL_ERR(trans,