iscsi-target: Fix incorrect np->np_thread NULL assignment

When shutting down a target there is a race condition between
iscsit_del_np() and __iscsi_target_login_thread().
The latter sets the thread pointer to NULL, and the former
tries to issue kthread_stop() on that pointer without any
synchronization.

This patch moves the np->np_thread NULL assignment into
iscsit_del_np(), after kthread_stop() has completed. It also
removes the signal_pending() + np_state check, and only
exits when kthread_should_stop() is true.

Reported-by: Hannes Reinecke <hare@suse.de>
Cc: <stable@vger.kernel.org> #3.12+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

2 files changed, 1 insertions, 6 deletions

diff --git a/drivers/target/iscsi/iscsi_target.c b/drivers/target/iscsi/iscsi_target.c
index 02182ab017b1..00867190413c 100644
--- a/drivers/target/iscsi/iscsi_target.c
+++ b/drivers/target/iscsi/iscsi_target.c
@@ -465,6 +465,7 @@ int iscsit_del_np(struct iscsi_np *np)
                  */
                 send_sig(SIGINT, np->np_thread, 1);
                 kthread_stop(np->np_thread);
+                np->np_thread = NULL;
         }
 
         np->np_transport->iscsit_free_np(np);
diff --git a/drivers/target/iscsi/iscsi_target_login.c b/drivers/target/iscsi/iscsi_target_login.c
index 4eb93b2b6473..e29279e6b577 100644
--- a/drivers/target/iscsi/iscsi_target_login.c
+++ b/drivers/target/iscsi/iscsi_target_login.c
@@ -1403,11 +1403,6 @@ old_sess_out:
 
 out:
         stop = kthread_should_stop();
-        if (!stop && signal_pending(current)) {
-                spin_lock_bh(&np->np_thread_lock);
-                stop = (np->np_thread_state == ISCSI_NP_THREAD_SHUTDOWN);
-                spin_unlock_bh(&np->np_thread_lock);
-        }
         /* Wait for another socket.. */
         if (!stop)
                 return 1;
@@ -1415,7 +1410,6 @@ exit:
         iscsi_stop_login_thread_timer(np);
         spin_lock_bh(&np->np_thread_lock);
         np->np_thread_state = ISCSI_NP_THREAD_EXIT;
-        np->np_thread = NULL;
         spin_unlock_bh(&np->np_thread_lock);
 
         return 0;