iwlwifi: mvm: don't check system_pm_mode without mutex held

When we want to stop TX'ing because we are suspending, we
have two options: either we check system_pm_mode or we
check the mvm's status that has a bit for the suspend
flow.
The latter is better because test_bit is atomic. Also
add a call to synchronize_net after we set the bit to
make sure that all the new Tx see the bit before we
actually complete the suspend flow.
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20210117130510.243c88781302.I5c0379c5a7e5d49410569e7fcd2fff7a419c6dea@changeidSigned-off-by: Luca Coelho <luciano.coelho@intel.com>

drivers/net/wireless/intel/iwlwifi/mvm/d3.c

@@ -997,6 +997,8 @@ static int __iwl_mvm_suspend(struct ieee80211_hw *hw,
 
 	set_bit(IWL_MVM_STATUS_IN_D3, &mvm->status);
 
+	synchronize_net();
+
 	vif = iwl_mvm_get_bss_vif(mvm);
 	if (IS_ERR_OR_NULL(vif)) {
 		ret = 1;

drivers/net/wireless/intel/iwlwifi/mvm/mac80211.c

@@ -816,8 +816,7 @@ void iwl_mvm_mac_itxq_xmit(struct ieee80211_hw *hw, struct ieee80211_txq *txq)
 	rcu_read_lock();
 	do {
 		while (likely(!mvmtxq->stopped &&
-			      (mvm->trans->system_pm_mode ==
-			       IWL_PLAT_PM_MODE_DISABLED))) {
+			      !test_bit(IWL_MVM_STATUS_IN_D3, &mvm->status))) {
 			skb = ieee80211_tx_dequeue(hw, txq);
 
 			if (!skb) {