qcacld-3.0: Synchronize hdd_driver_unload against other vdev trans

Unloading the driver is a driver transition. As a part of this driver
unload, the PLD calls the pld_remove which is a psoc transition. This is
the reason why the driver unload is currently not being protected as
there is a call to psoc transition within it.

This absence of locking can lead to potential deadlock scenario. Assume the
example of add_virtual_interface and rmmod coming in parallel.

	T1: add_virtual_interface (starts a vdev_trans)

	T2: rmmod comes in parallel
		-> unregister_driver goes to PLD
		-> PLD calls pld_remove (psoc_trans waits due to T1)

	T1: add_virtual_interface continues
		-> Calls idle_restart that goes to PLD
		-> PLD waits from pld_remove (T2) to complete first

	T1 and T2 are waiting for each other to exit resulting in
	deadlock.

To resolve this, add a driver_trans_start_wait to hdd_driver_unload.
This will ensure that either the unload waits for all other trans to be
completed before proceeding or set the driver_load_unload flag which
will result in upcoming trans to get rejected.

Change-Id: I64b03843065e5eef7c2be209c1f8cb936bdd0742
CRs-Fixed: 2683032

core/hdd/src/wlan_hdd_main.c

@@ -15499,6 +15499,20 @@ static void hdd_driver_unload(void)
 	pr_info("%s: Unloading driver v%s\n", WLAN_MODULE_NAME,
 		QWLAN_VERSIONSTR);
 
+	/*
+	 * Wait for any trans to complete and then start the driver trans
+	 * for the unload. This will ensure that the driver trans proceeds only
+	 * after all trans have been completed. As a part of this trans, set
+	 * the driver load/unload flag to further ensure that any upcoming
+	 * trans are rejected via wlan_hdd_validate_context.
+	 */
+	status = osif_driver_sync_trans_start_wait(&driver_sync);
+	QDF_BUG(QDF_IS_STATUS_SUCCESS(status));
+	if (QDF_IS_STATUS_ERROR(status)) {
+		hdd_err("Unable to unload wlan; status:%u", status);
+		return;
+	}
+
 	hif_ctx = cds_get_context(QDF_MODULE_ID_HIF);
 	if (hif_ctx) {
 		/*
@@ -15520,6 +15534,12 @@ static void hdd_driver_unload(void)
 		hdd_bus_bw_compute_timer_stop(hdd_ctx);
 	}
 
+	/*
+	 * Stop the trans before calling unregister_driver as that involves a
+	 * call to pld_remove which in itself is a psoc transaction
+	 */
+	osif_driver_sync_trans_stop(driver_sync);
+
 	/* trigger SoC remove */
 	wlan_hdd_unregister_driver();