scsi: ibmvfc: Fix potential race in ibmvfc_wait_for_ops()

For various EH activities the ibmvfc driver uses ibmvfc_wait_for_ops() to
wait for the completion of commands that match a given criteria be it
cancel key, or specific LUN. With recent changes commands are completed
outside the lock in bulk by removing them from the sent list and adding
them to a private completion list. This introduces a potential race in
ibmvfc_wait_for_ops() since the criteria for a command to be outstanding is
no longer simply being on the sent list, but instead not being on the free
list.

Avoid this race by scanning the entire command event pool and checking that
any matching command that ibmvfc needs to wait on is not already on the
free list.

Link: https://lore.kernel.org/r/20210319205029.312969-2-tyreld@linux.ibm.com
Fixes: 1f4a4a19 ("scsi: ibmvfc: Complete commands outside the host/queue lock")
Reviewed-by: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: Tyrel Datwyler <tyreld@linux.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/ibmvscsi/ibmvfc.c

@@ -2371,6 +2371,24 @@ static int ibmvfc_match_lun(struct ibmvfc_event *evt, void *device)
 	return 0;
 }
 
+/**
+ * ibmvfc_event_is_free - Check if event is free or not
+ * @evt:	ibmvfc event struct
+ *
+ * Returns:
+ *	true / false
+ **/
+static bool ibmvfc_event_is_free(struct ibmvfc_event *evt)
+{
+	struct ibmvfc_event *loop_evt;
+
+	list_for_each_entry(loop_evt, &evt->queue->free, queue_list)
+		if (loop_evt == evt)
+			return true;
+
+	return false;
+}
+
 /**
  * ibmvfc_wait_for_ops - Wait for ops to complete
  * @vhost:	ibmvfc host struct
@@ -2385,7 +2403,7 @@ static int ibmvfc_wait_for_ops(struct ibmvfc_host *vhost, void *device,
 {
 	struct ibmvfc_event *evt;
 	DECLARE_COMPLETION_ONSTACK(comp);
-	int wait;
+	int wait, i;
 	unsigned long flags;
 	signed long timeout = IBMVFC_ABORT_WAIT_TIMEOUT * HZ;
 
@@ -2393,12 +2411,15 @@ static int ibmvfc_wait_for_ops(struct ibmvfc_host *vhost, void *device,
 	do {
 		wait = 0;
 		spin_lock_irqsave(&vhost->crq.l_lock, flags);
-		list_for_each_entry(evt, &vhost->crq.sent, queue_list) {
+		for (i = 0; i < vhost->crq.evt_pool.size; i++) {
+			evt = &vhost->crq.evt_pool.events[i];
+			if (!ibmvfc_event_is_free(evt)) {
 				if (match(evt, device)) {
 					evt->eh_comp = &comp;
 					wait++;
 				}
 			}
+		}
 		spin_unlock_irqrestore(&vhost->crq.l_lock, flags);
 
 		if (wait) {
@@ -2407,12 +2428,15 @@ static int ibmvfc_wait_for_ops(struct ibmvfc_host *vhost, void *device,
 			if (!timeout) {
 				wait = 0;
 				spin_lock_irqsave(&vhost->crq.l_lock, flags);
-				list_for_each_entry(evt, &vhost->crq.sent, queue_list) {
+				for (i = 0; i < vhost->crq.evt_pool.size; i++) {
+					evt = &vhost->crq.evt_pool.events[i];
+					if (!ibmvfc_event_is_free(evt)) {
 						if (match(evt, device)) {
 							evt->eh_comp = NULL;
 							wait++;
 						}
 					}
+				}
 				spin_unlock_irqrestore(&vhost->crq.l_lock, flags);
 				if (wait)
 					dev_err(vhost->dev, "Timed out waiting for aborted commands\n");