scsi: target: core: Fix deadlock due to recursive locking

The following call trace shows a deadlock issue due to recursive locking of
mutex "device_mutex". First lock acquire is in target_for_each_device() and
second in target_free_device().

 PID: 148266   TASK: ffff8be21ffb5d00  CPU: 10   COMMAND: "iscsi_ttx"
  #0 [ffffa2bfc9ec3b18] __schedule at ffffffffa8060e7f
  #1 [ffffa2bfc9ec3ba0] schedule at ffffffffa8061224
  #2 [ffffa2bfc9ec3bb8] schedule_preempt_disabled at ffffffffa80615ee
  #3 [ffffa2bfc9ec3bc8] __mutex_lock at ffffffffa8062fd7
  #4 [ffffa2bfc9ec3c40] __mutex_lock_slowpath at ffffffffa80631d3
  #5 [ffffa2bfc9ec3c50] mutex_lock at ffffffffa806320c
  torvalds#6 [ffffa2bfc9ec3c68] target_free_device at ffffffffc0935998 [target_core_mod]
  torvalds#7 [ffffa2bfc9ec3c90] target_core_dev_release at ffffffffc092f975 [target_core_mod]
  torvalds#8 [ffffa2bfc9ec3ca0] config_item_put at ffffffffa79d250f
  torvalds#9 [ffffa2bfc9ec3cd0] config_item_put at ffffffffa79d2583
 torvalds#10 [ffffa2bfc9ec3ce0] target_devices_idr_iter at ffffffffc0933f3a [target_core_mod]
 torvalds#11 [ffffa2bfc9ec3d00] idr_for_each at ffffffffa803f6fc
 torvalds#12 [ffffa2bfc9ec3d60] target_for_each_device at ffffffffc0935670 [target_core_mod]
 torvalds#13 [ffffa2bfc9ec3d98] transport_deregister_session at ffffffffc0946408 [target_core_mod]
 torvalds#14 [ffffa2bfc9ec3dc8] iscsit_close_session at ffffffffc09a44a6 [iscsi_target_mod]
 torvalds#15 [ffffa2bfc9ec3df0] iscsit_close_connection at ffffffffc09a4a88 [iscsi_target_mod]
 torvalds#16 [ffffa2bfc9ec3df8] finish_task_switch at ffffffffa76e5d07
 torvalds#17 [ffffa2bfc9ec3e78] iscsit_take_action_for_connection_exit at ffffffffc0991c23 [iscsi_target_mod]
 torvalds#18 [ffffa2bfc9ec3ea0] iscsi_target_tx_thread at ffffffffc09a403b [iscsi_target_mod]
 torvalds#19 [ffffa2bfc9ec3f08] kthread at ffffffffa76d8080
 torvalds#20 [ffffa2bfc9ec3f50] ret_from_fork at ffffffffa8200364

Fixes: 36d4cb4 ("scsi: target: Avoid that EXTENDED COPY commands trigger lock inversion")
Signed-off-by: Junxiao Bi <junxiao.bi@oracle.com>
Link: https://lore.kernel.org/r/20230918225848.66463-1-junxiao.bi@oracle.com
Reviewed-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/target/target_core_device.c

@@ -843,7 +843,6 @@ sector_t target_to_linux_sector(struct se_device *dev, sector_t lb)
 EXPORT_SYMBOL(target_to_linux_sector);
 
 struct devices_idr_iter {
-	struct config_item *prev_item;
 	int (*fn)(struct se_device *dev, void *data);
 	void *data;
 };
@@ -853,11 +852,9 @@ static int target_devices_idr_iter(int id, void *p, void *data)
 {
 	struct devices_idr_iter *iter = data;
 	struct se_device *dev = p;
+	struct config_item *item;
 	int ret;
 
-	config_item_put(iter->prev_item);
-	iter->prev_item = NULL;
-
 	/*
 	 * We add the device early to the idr, so it can be used
 	 * by backend modules during configuration. We do not want
@@ -867,12 +864,13 @@ static int target_devices_idr_iter(int id, void *p, void *data)
 	if (!target_dev_configured(dev))
 		return 0;
 
-	iter->prev_item = config_item_get_unless_zero(&dev->dev_group.cg_item);
-	if (!iter->prev_item)
+	item = config_item_get_unless_zero(&dev->dev_group.cg_item);
+	if (!item)
 		return 0;
 	mutex_unlock(&device_mutex);
 
 	ret = iter->fn(dev, iter->data);
+	config_item_put(item);
 
 	mutex_lock(&device_mutex);
 	return ret;
@@ -895,7 +893,6 @@ int target_for_each_device(int (*fn)(struct se_device *dev, void *data),
 	mutex_lock(&device_mutex);
 	ret = idr_for_each(&devices_idr, target_devices_idr_iter, &iter);
 	mutex_unlock(&device_mutex);
-	config_item_put(iter.prev_item);
 	return ret;
 }