scsi: target: iscsi: Fix use-after-free in iscsit_dec_conn_usage_count()

In the Linux kernel, the following vulnerability has been resolved:

scsi: target: iscsi: Fix use-after-free in iscsit_dec_conn_usage_count()

In iscsit_dec_conn_usage_count(), the function calls complete() while holding the conn->conn_usage_lock. As soon as complete() is invoked, the waiter (such as iscsit_close_connection()) may wake up and proceed to free the iscsit_conn structure.

If the waiter frees the memory before the current thread reaches spin_unlock_bh(), it results in a KASAN slab-use-after-free as the function attempts to release a lock within the already-freed connection structure.

Fix this by releasing the spinlock before calling complete().