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iscsi-target: fix iscsit_del_np deadlock on unload

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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
db6077fd0b, 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>
This commit is contained in:
Mikulas Patocka 2014-06-23 13:42:37 -04:00 committed by Nicholas Bellinger
parent ac5ccdba3a
commit 81a9c5e72b
1 changed files with 7 additions and 6 deletions
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13
drivers/target/iscsi/iscsi_target_login.c
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@ -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;
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