[master] 4df4d2a49 avoid the STV_close() race for now

[Nils Goroll]

commit 4df4d2a497727a671d2f2b64d3ccd03fc4cbc3d6
Author: Nils Goroll <nils.goroll at uplex.de>
Date:   Tue Jan 14 15:44:24 2020 +0100

    avoid the STV_close() race for now
    
    See #3190

diff --git a/bin/varnishd/storage/storage_umem.c b/bin/varnishd/storage/storage_umem.c
index 0c5c06e1c..dc53a1d60 100644
--- a/bin/varnishd/storage/storage_umem.c
+++ b/bin/varnishd/storage/storage_umem.c
@@ -431,8 +431,12 @@ smu_close(const struct stevedore *st, int warn)
 	CAST_OBJ_NOTNULL(smu_sc, st->priv, SMU_SC_MAGIC);
 	if (warn)
 		return;
+
+#ifdef WORKAROUND_3190
+	/* see ticket 3190 for explanation */
 	umem_cache_destroyf(smu_sc->smu_cache);
 	smu_sc->smu_cache = NULL;
+#endif
 
 	/*
 	   XXX TODO?