[dm-devel] [PATCH] multipathd: fix SIGUSR2 handling

[tang.junhui at zte.com.cn]

From: "tang.junhui" <tang.junhui at zte.com.cn>

SIGUSR2 is not blocked by default, it would cause bellow conflict
in removing of the last path:
-------------------------------------------------------------
uevent processing thread                 | waiter thread
-----------------------------------------|-------------------
uev_remove_path()                        |   waiteventloop()
  lock(&vecs->lock)                      |
  ev_remove_path()                       |     
    dm_queue_if_no_path()----------------|----> dm_task_run()	
    flush_map()                          |      |
      remove_map_and_stop_waiter()       |      -> pthread_cleanup_push(cleanup_lock, &waiter->vecs->lock);
        _remove_map()                    |         lock(&waiter->vecs->lock)//wait for the locker	
          stop_waiter_thread()           |         
            pthread_cancel(thread)       |          
            pthread_kill(thread,SIGUSR2)-|------> sigusr2 (int sig)
                                         |          condlog()
                                         |          fprintf() //it has test cancel point
                                         |          cleanup_lock() //thread cancel, and pop, which unlock the 
                                         |                           locker of uevent processing thread 
--------------------------------------------------------------
Since SIGUSR2 is only needed when waiter thread running in dm_task_run(),
and it has already been unblocked before dm_task_run(), so this patch block 
SIGUSR2 for other times.

Change-Id: I8c46292dc954415764ebbe054498b4f7ea53c1c6
Signed-off-by: tang.junhui <tang.junhui at zte.com.cn>
---
 multipathd/main.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/multipathd/main.c b/multipathd/main.c
index adc3258..fe69abd 100644
--- a/multipathd/main.c
+++ b/multipathd/main.c
@@ -2181,6 +2181,12 @@ sigusr2 (int sig)
 static void
 signal_init(void)
 {
+	sigset_t set;
+
+	sigemptyset(&set);
+	sigaddset(&set, SIGUSR2);
+	pthread_sigmask(SIG_SETMASK, &set, NULL);
+
 	signal_set(SIGHUP, sighup);
 	signal_set(SIGUSR1, sigusr1);
 	signal_set(SIGUSR2, sigusr2);
-- 
2.8.1.windows.1