iscsi-target: Fix iscsit_start_kthreads failure OOPs

This patch fixes a regression introduced with the following commit
in v4.0-rc1 code, where a iscsit_start_kthreads() failure triggers
a NULL pointer dereference OOPs:

    commit 88dcd2dab5c23b1c9cfc396246d8f476c872f0ca
    Author: Nicholas Bellinger <nab@linux-iscsi.org>
    Date:   Thu Feb 26 22:19:15 2015 -0800

        iscsi-target: Convert iscsi_thread_set usage to kthread.h

To address this bug, move iscsit_start_kthreads() immediately
preceeding the transmit of last login response, before signaling
a successful transition into full-feature-phase within existing
iscsi_target_do_tx_login_io() logic.

This ensures that no target-side resource allocation failures can
occur after the final login response has been successfully sent.

Also, it adds a iscsi_conn->rx_login_comp to allow the RX thread
to sleep to prevent other socket related failures until the final
iscsi_post_login_handler() call is able to complete.

Cc: Sagi Grimberg <sagig@mellanox.com>
Cc: <stable@vger.kernel.org> # v3.10+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

1 files changed, 15 insertions, 3 deletions

diff --git a/drivers/target/iscsi/iscsi_target.c b/drivers/target/iscsi/iscsi_target.c
index afab32376126..202a42858f25 100644
--- a/drivers/target/iscsi/iscsi_target.c
+++ b/drivers/target/iscsi/iscsi_target.c
@@ -3998,7 +3998,13 @@ get_immediate:
 	}
 
 transport_err:
-	iscsit_take_action_for_connection_exit(conn);
+	/*
+	 * Avoid the normal connection failure code-path if this connection
+	 * is still within LOGIN mode, and iscsi_np process context is
+	 * responsible for cleaning up the early connection failure.
+	 */
+	if (conn->conn_state != TARG_CONN_STATE_IN_LOGIN)
+		iscsit_take_action_for_connection_exit(conn);
 out:
 	return 0;
 }
@@ -4082,7 +4088,7 @@ reject:
 
 int iscsi_target_rx_thread(void *arg)
 {
-	int ret;
+	int ret, rc;
 	u8 buffer[ISCSI_HDR_LEN], opcode;
 	u32 checksum = 0, digest = 0;
 	struct iscsi_conn *conn = arg;
@@ -4092,10 +4098,16 @@ int iscsi_target_rx_thread(void *arg)
 	 * connection recovery / failure event can be triggered externally.
 	 */
 	allow_signal(SIGINT);
+	/*
+	 * Wait for iscsi_post_login_handler() to complete before allowing
+	 * incoming iscsi/tcp socket I/O, and/or failing the connection.
+	 */
+	rc = wait_for_completion_interruptible(&conn->rx_login_comp);
+	if (rc < 0)
+		return 0;
 
 	if (conn->conn_transport->transport_type == ISCSI_INFINIBAND) {
 		struct completion comp;
-		int rc;
 
 		init_completion(&comp);
 		rc = wait_for_completion_interruptible(&comp);