[master] e9948061d From VTEST:

[Poul-Henning Kamp]

commit e9948061d30255fb2eafc1fa5f5e905aba774789
Author: Poul-Henning Kamp <phk at FreeBSD.org>
Date:   Mon Apr 8 07:35:42 2019 +0000

    From VTEST:
    
        Reinitialize cyclic barrier only once per cycle
    
        It was done for all threads syncing on a barrier. The one reaching the limit but
        also all waiting threads. So it could be reset by a thread while others have
        already started another round, leading to an deadlock (because some increments
        will be lost then).
    
        Now, cyclic barrier is reset for a new round by the thread reaching the limit
        and only this one.
    
    Author: Christopher Faulet <cfaulet at haproxy.com>

diff --git a/bin/varnishtest/vtc_barrier.c b/bin/varnishtest/vtc_barrier.c
index e7fc1e5ae..cd0063cf5 100644
--- a/bin/varnishtest/vtc_barrier.c
+++ b/bin/varnishtest/vtc_barrier.c
@@ -274,15 +274,14 @@ barrier_cond_sync(struct barrier *b, struct vtclog *vl)
 
 	if (++b->waiters == b->expected) {
 		vtc_log(vl, 4, "Barrier(%s) wake %u", b->name, b->expected);
+		if (b->cyclic)
+			b->waiters = 0;
 		AZ(pthread_cond_broadcast(&b->cond));
 	} else {
 		vtc_log(vl, 4, "Barrier(%s) wait %u of %u",
 		    b->name, b->waiters, b->expected);
 		AZ(pthread_cond_wait(&b->cond, &b->mtx));
 	}
-
-	if (b->cyclic)
-		b->waiters = 0;
 }
 
 static void