• Mikulas Patocka's avatar
    iscsi-target: fix iscsit_del_np deadlock on unload · 81a9c5e7
    Mikulas Patocka authored
    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: default avatarMikulas Patocka <mpatocka@redhat.com>
    Cc: stable@vger.kernel.org
    Signed-off-by: default avatarNicholas Bellinger <nab@linux-iscsi.org>
    81a9c5e7
iscsi_target_login.c 39 KB