[PATCH 3.14 05/59] iscsi-target: fix iscsit_del_np deadlock on unload

Greg Kroah-Hartman
2014-07-04T22:48:00Z

From: Mikulas Patocka <mpatocka@redhat.com>

commit 81a9c5e72bdf7109a65102ca61d8cbd722cf4021 upstream.

On uniprocessor preemptible kernel, target core deadlocks on unload. The
following events happen:
* iscsit_del_np is called
* it calls send_sig(SIGINT, np->np_thread, 1);
* the scheduler switches to the np_thread
* the np_thread is woken up, it sees that kthread_should_stop() returns
false, so it doesn't terminate
* the np_thread clears signals with flush_signals(current); and goes back
to sleep in iscsit_accept_np
* the scheduler switches back to iscsit_del_np
* iscsit_del_np calls kthread_stop(np->np_thread);
* the np_thread is waiting in iscsit_accept_np and it doesn't respond to
kthread_stop

The deadlock could be resolved if the administrator sends SIGINT signal to
the np_thread with killall -INT iscsi_np

The reproducible deadlock was introduced in commit
db6077fd0b7dd41dc6ff18329cec979379071f87, but the thread-stopping code was
racy even before.

This patch fixes the problem. Using kthread_should_stop to stop the
np_thread is unreliable, so we test np_thread_state instead. If
np_thread_state equals ISCSI_NP_THREAD_SHUTDOWN, the thread exits.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/target/iscsi/iscsi_target_login.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)

--- a/drivers/target/iscsi/iscsi_target_login.c
+++ b/drivers/target/iscsi/iscsi_target_login.c
@@ -1196,7 +1196,7 @@ old_sess_out:
static int __iscsi_target_login_thread(struct iscsi_np *np)
{
u8 *buffer, zero_tsih = 0;
- int ret = 0, rc, stop;
+ int ret = 0, rc;
struct iscsi_conn *conn = NULL;
struct iscsi_login *login;
struct iscsi_portal_group *tpg = NULL;
@@ -1210,6 +1210,9 @@ static int __iscsi_target_login_thread(s
if (np->np_thread_state == ISCSI_NP_THREAD_RESET) {
np->np_thread_state = ISCSI_NP_THREAD_ACTIVE;
complete(&np->np_restart_comp);
+ } else if (np->np_thread_state == ISCSI_NP_THREAD_SHUTDOWN) {
+ spin_unlock_bh(&np->np_thread_lock);
+ goto exit;
} else {
np->np_thread_state = ISCSI_NP_THREAD_ACTIVE;
}
@@ -1402,10 +1405,8 @@ old_sess_out:
}

out:
- stop = kthread_should_stop();
- /* Wait for another socket.. */
- if (!stop)
- return 1;
+ return 1;
+
exit:
iscsi_stop_login_thread_timer(np);
spin_lock_bh(&np->np_thread_lock);
@@ -1422,7 +1423,7 @@ int iscsi_target_login_thread(void *arg)

allow_signal(SIGINT);

- while (!kthread_should_stop()) {
+ while (1) {
ret = __iscsi_target_login_thread(np);
/*
* We break and exit here unless another sock_accept() call