Commit 81a9c5e7 authored Jun 23, 2014 by Mikulas Patocka Committed by Nicholas Bellinger Jun 27, 2014

iscsi-target: fix iscsit_del_np deadlock on unload



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
db6077fd, 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>
Cc: stable@vger.kernel.org
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

parent ac5ccdba

drivers/target/iscsi/iscsi_target_login.c

+7 −6

Original line number	Diff line number	Diff line
		@@ -1216,7 +1216,7 @@ 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;
		@@ -1230,6 +1230,9 @@ static int __iscsi_target_login_thread(struct iscsi_np *np)
		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;
		}
		@@ -1422,10 +1425,8 @@ old_sess_out:
		}

		out:
		stop = kthread_should_stop();
		/* Wait for another socket.. */
		if (!stop)
		return 1;

		exit:
		iscsi_stop_login_thread_timer(np);
		spin_lock_bh(&np->np_thread_lock);
		@@ -1442,7 +1443,7 @@ 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