scsi: mpt3sas: Fix deadlock while cancelling the running firmware event

Do not cancel current running firmware event work if the event type is
different from MPT3SAS_REMOVE_UNRESPONDING_DEVICES.  Otherwise a deadlock
can be observed while cancelling the current firmware event work if a hard
reset operation is called as part of processing the current event.

Link: https://lore.kernel.org/r/20210518051625.1596742-2-suganath-prabu.subramani@broadcom.com
Signed-off-by: Suganath Prabu S <suganath-prabu.subramani@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/mpt3sas/mpt3sas_scsih.c

@@ -3697,6 +3697,28 @@ _scsih_fw_event_cleanup_queue(struct MPT3SAS_ADAPTER *ioc)
 	ioc->fw_events_cleanup = 1;
 	while ((fw_event = dequeue_next_fw_event(ioc)) ||
 	     (fw_event = ioc->current_event)) {
+
+		/*
+		 * Don't call cancel_work_sync() for current_event
+		 * other than MPT3SAS_REMOVE_UNRESPONDING_DEVICES;
+		 * otherwise we may observe deadlock if current
+		 * hard reset issued as part of processing the current_event.
+		 *
+		 * Orginal logic of cleaning the current_event is added
+		 * for handling the back to back host reset issued by the user.
+		 * i.e. during back to back host reset, driver use to process
+		 * the two instances of MPT3SAS_REMOVE_UNRESPONDING_DEVICES
+		 * event back to back and this made the drives to unregister
+		 * the devices from SML.
+		 */
+
+		if (fw_event == ioc->current_event &&
+		    ioc->current_event->event !=
+		    MPT3SAS_REMOVE_UNRESPONDING_DEVICES) {
+			ioc->current_event = NULL;
+			continue;
+		}
+
 		/*
 		 * Wait on the fw_event to complete. If this returns 1, then
 		 * the event was never executed, and we need a put for the