[master] fb342dd document a potential race

[Nils Goroll]

commit fb342dde523c3b87a62d2186422071311ae18fdd
Author: Nils Goroll <nils.goroll at uplex.de>
Date:   Mon Apr 30 13:48:16 2018 +0200

    document a potential race
    
    closes #2625

diff --git a/bin/varnishd/cache/cache_tcp_pool.c b/bin/varnishd/cache/cache_tcp_pool.c
index 86777ae..fd416e8 100644
--- a/bin/varnishd/cache/cache_tcp_pool.c
+++ b/bin/varnishd/cache/cache_tcp_pool.c
@@ -667,6 +667,10 @@ VTP_Ref(const struct suckaddr *ip4, const struct suckaddr *ip6, const char *uds,
 	if (cp != NULL)
 		return (cp->priv);
 
+	/*
+	 * this is racy - we could end up with additional pools on the same id /
+	 * destination address with just a single connection
+	 */
 	ALLOC_OBJ(tp, TCP_POOL_MAGIC);
 	AN(tp);
 	if (uds != NULL) {