nvmet-fc: avoid scheduling association deletion twice

When forcefully shutting down a port via the configfs interface,
nvmet_port_subsys_drop_link() first calls nvmet_port_del_ctrls() and
then nvmet_disable_port(). Both functions will eventually schedule all
remaining associations for deletion.

The current implementation checks whether an association is about to be
removed, but only after the work item has already been scheduled. As a
result, it is possible for the first scheduled work item to free all
resources, and then for the same work item to be scheduled again for
deletion.

Because the association list is an RCU list, it is not possible to take
a lock and remove the list entry directly, so it cannot be looked up
again. Instead, a flag (terminating) must be used to determine whether
the association is already in the process of being deleted.

Reported-by: Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Closes: https://lore.kernel.org/all/rsdinhafrtlguauhesmrrzkybpnvwantwmyfq2ih5aregghax5@mhr7v3eryci3/
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Daniel Wagner <wagi@kernel.org>
Signed-off-by: Keith Busch <kbusch@kernel.org>

Author: igaw

drivers/nvme/target/fc.c

@@ -1075,6 +1075,14 @@ nvmet_fc_delete_assoc_work(struct work_struct *work)
 static void
 nvmet_fc_schedule_delete_assoc(struct nvmet_fc_tgt_assoc *assoc)
 {
+	int terminating;
+
+	terminating = atomic_xchg(&assoc->terminating, 1);
+
+	/* if already terminating, do nothing */
+	if (terminating)
+		return;
+
 	nvmet_fc_tgtport_get(assoc->tgtport);
 	if (!queue_work(nvmet_wq, &assoc->del_work))
 		nvmet_fc_tgtport_put(assoc->tgtport);
@@ -1202,13 +1210,7 @@ nvmet_fc_delete_target_assoc(struct nvmet_fc_tgt_assoc *assoc)
 {
 	struct nvmet_fc_tgtport *tgtport = assoc->tgtport;
 	unsigned long flags;
-	int i, terminating;
-
-	terminating = atomic_xchg(&assoc->terminating, 1);
-
-	/* if already terminating, do nothing */
-	if (terminating)
-		return;
+	int i;
 
 	spin_lock_irqsave(&tgtport->lock, flags);
 	list_del_rcu(&assoc->a_list);