Make memstv assertions more precise

Because of #14 I would like to understand if #13 is really a genuine
bug or some odd consequence

src/fellow_storage.c

@@ -238,6 +238,12 @@ stv_stvfe(const struct stevedore *stv)
  * memocs mutate to dskocs for memory LRU
  */
 
+#define assert_memstv(stvfe, stv) do {		\
+	assert(stv != NULL);			\
+	assert(stv != stvfe->dskstv);		\
+	assert(stv == stvfe->memstv);		\
+	} while (0)
+
 static inline struct fellow_cache_obj *
 stvfe_memoc_fco(const struct stevedore *stv, const struct stvfe *stvfe,
     const struct objcore *oc)
@@ -245,7 +251,7 @@ stvfe_memoc_fco(const struct stevedore *stv, const struct stvfe *stvfe,
 	void *priv;
 
 	CHECK_OBJ_NOTNULL(stvfe, STVFE_MAGIC);
-	assert(stv == stvfe->memstv);
+	assert_memstv(stvfe, stv);
 	AN(oc->stobj->priv2);
 	// CST implies a memory barrier
 	priv = __atomic_load_n(/*lint --e(605)*/ &oc->stobj->priv,
@@ -370,7 +376,7 @@ sfemem_free(struct worker *wrk, struct objcore *memoc)
 	const struct objhead *oh = memoc->objhead;
 
 	CHECK_OBJ_NOTNULL(oh, OBJHEAD_MAGIC);
-	assert(stv == stvfe->memstv);
+	assert_memstv(stvfe, stv);
 
 	AN(stv->lru);
 	// ref fellow_busy_done()
@@ -846,7 +852,7 @@ sfemem_getattr(struct worker *wrk, struct objcore *memoc, enum obj_attr attr,
 	size_t len;
 	void *r;
 
-	assert(stv == stvfe->memstv);
+	assert_memstv(stvfe, stv);
 
 	r = fellow_cache_obj_getattr(stvfe->fc, fco, attr, &len);
 	if (slen)
@@ -898,7 +904,7 @@ sfemem_setattr(struct worker *wrk, struct objcore *memoc, enum obj_attr attr,
 	const struct stevedore *stv = oc_stv(wrk, memoc);
 	const struct stvfe *stvfe = stv_stvfe(stv);
 
-	assert(stv == stvfe->memstv);
+	assert_memstv(stvfe, stv);
 	assert(len >= 0);
 
 	return (fellow_busy_setattr(sfe_fbo(memoc), attr, (size_t)len, ptr));
@@ -911,7 +917,7 @@ sfemem_touch(struct worker *wrk, struct objcore *memoc, vtim_real now)
 	const struct stvfe *stvfe = stv_stvfe(stv);
 	struct fellow_cache_obj *fco = stvfe_memoc_fco(stv, stvfe, memoc);
 
-	assert(stv == stvfe->memstv);
+	assert_memstv(stvfe, stv);
 
 	if (/*lint --e(641)*/ memoc->flags & OC_F_PRIVATE ||
 	    isnan(memoc->last_lru))
@@ -1607,7 +1613,7 @@ stvfe_mutate(struct worker *wrk, struct objcore *oc)
 			const struct stevedore *stv = oc_stv(wrk, oc);
 			const struct stvfe *stvfe = stv_stvfe(stv);
 
-			assert(stv == stvfe->memstv);
+			assert_memstv(stvfe, stv);
 			AN(oc->stobj->priv);
 			AN(oc->stobj->priv2);