Fix deadlock in case of evconnlistener_disable() in parallel with callback

I've got an issue when stop evconnlistener not in the event_base_loop()
thread. evconnlistener_disable() acquired lev->lock, if the same time,
user callbacks is runing, the event thread released lock, after callback
finished, it try to aquire the lock again, I think this makes conflict:

Here is backtraces:

thread 1:
    0  __lll_lock_wait (futex=futex@entry=0x555555559a60, private=0) at lowlevellock.c:52
    1  0x00007ffff7f2a131 in __GI___pthread_mutex_lock (mutex=0x555555559a60) at ../nptl/pthread_mutex_lock.c:115
    2  0x00007ffff7f424c9 in evthread_posix_lock (mode=0, lock_=0x555555559a60) at evthread_pthread.c:79
    3  0x00007ffff7f7dc12 in listener_read_cb (fd=7, what=2, p=0x5555555599a0) at listener.c:439
    4  0x00007ffff7f6d758 in event_persist_closure (base=0x555555559370, ev=0x5555555599d8) at event.c:1645
    5  0x00007ffff7f6da60 in event_process_active_single_queue (base=0x555555559370, activeq=0x5555555597e0,
       max_to_process=2147483647, endtime=0x0) at event.c:1704
    6  0x00007ffff7f6e018 in event_process_active (base=0x555555559370) at event.c:1805
    7  0x00007ffff7f6e92a in event_base_loop (base=0x555555559370, flags=0) at event.c:2047
    8  0x0000555555555449 in main () at test_listen.c:67

thread 2:
    0  futex_wait_cancelable (private=<optimized out>, expected=0, futex_word=0x555555559858) at ../sysdeps/nptl/futex-internal.h:183
    1  __pthread_cond_wait_common (abstime=0x0, clockid=0, mutex=0x555555559800, cond=0x555555559830) at pthread_cond_wait.c:508
    2  __pthread_cond_wait (cond=0x555555559830, mutex=0x555555559800) at pthread_cond_wait.c:638
    3  0x00007ffff7f426f3 in evthread_posix_cond_wait (cond_=0x555555559830, lock_=0x555555559800, tv=0x0) at evthread_pthread.c:162
    4  0x00007ffff7f70bc5 in event_del_nolock_ (ev=0x5555555599d8, blocking=2) at event.c:2934
    5  0x00007ffff7f70748 in event_del_ (ev=0x5555555599d8, blocking=2) at event.c:2821
    6  0x00007ffff7f707a1 in event_del (ev=0x5555555599d8) at event.c:2830
    7  0x00007ffff7f7d76e in event_listener_disable (lev=0x5555555599a0) at listener.c:343
    8  0x00007ffff7f7d6e5 in evconnlistener_disable (lev=0x5555555599a0) at listener.c:325
    9  0x00005555555552c3 in disable_thread (arg=0x5555555599a0) at test_listen.c:27
    10 0x00007ffff7f27609 in start_thread (arg=<optimized out>) at pthread_create.c:477
    11 0x00007ffff7e4e293 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

1 files changed, 0 insertions, 4 deletions

diff --git a/listener.c b/listener.c
index bf55f7b5..125c7286 100644
--- a/listener.c
+++ b/listener.c
@@ -433,10 +433,8 @@ listener_read_cb(evutil_socket_t fd, short what, void *p)
 		++lev->refcnt;
 		cb = lev->cb;
 		user_data = lev->user_data;
-		UNLOCK(lev);
 		cb(lev, new_fd, (struct sockaddr*)&ss, (int)socklen,
 		    user_data);
-		LOCK(lev);
 		if (lev->refcnt == 1) {
 			int freed = listener_decref_and_unlock(lev);
 			EVUTIL_ASSERT(freed);
@@ -458,9 +456,7 @@ listener_read_cb(evutil_socket_t fd, short what, void *p)
 		++lev->refcnt;
 		errorcb = lev->errorcb;
 		user_data = lev->user_data;
-		UNLOCK(lev);
 		errorcb(lev, user_data);
-		LOCK(lev);
 		listener_decref_and_unlock(lev);
 	} else {
 		event_sock_warn(fd, "Error from accept() call");