[SCSI] iscsi_tcp: support PF_MEMALLOC/__GFP_MEMALLOC

This patch has software iscsi use PF_MEMALLOC/__GFP_MEMALLOC
to be able to better support swap over iscsi disks similar to
what was added for nbd.

Signed-off-by: Mike Christie <[e-mail]>
Signed-off-by: James Bottomley <[e-mail]>

drivers/scsi/iscsi_tcp.c

···
 static int iscsi_sw_tcp_pdu_xmit(struct iscsi_task *task)
 {
 	struct iscsi_conn *conn = task->conn;
-	int rc;
+	unsigned long pflags = current->flags;
+	int rc = 0;
+
+	current->flags |= PF_MEMALLOC;
 
 	while (iscsi_sw_tcp_xmit_qlen(conn)) {
 		rc = iscsi_sw_tcp_xmit(conn);
-		if (rc == 0)
-			return -EAGAIN;
+		if (rc == 0) {
+			rc = -EAGAIN;
+			break;
+		}
 		if (rc < 0)
-			return rc;
+			break;
+		rc = 0;
 	}
 
-	return 0;
+	tsk_restore_flags(current, pflags, PF_MEMALLOC);
+	return rc;
 }
 
 /*
···
 	sk->sk_reuse = SK_CAN_REUSE;
 	sk->sk_sndtimeo = 15 * HZ; /* FIXME: make it configurable */
 	sk->sk_allocation = GFP_ATOMIC;
+	sk_set_memalloc(sk);
 
 	iscsi_sw_tcp_conn_set_callbacks(conn);
 	tcp_sw_conn->sendpage = tcp_sw_conn->sock->ops->sendpage;