ck_bag: Validate block_size > block_overhead during ck_bag_init.

Check ck_bag_init return value in unit test.

regressions/ck_bag/validate/order.c

@@ -250,7 +250,10 @@ main(int argc, char **argv)
 	ck_epoch_init(&epoch_bag, 100);
 	ck_epoch_register(&epoch_bag, &epoch_wr);
 	ck_bag_allocator_set(&allocator, sizeof(struct bag_epoch));
-	ck_bag_init(&bag, b, CK_BAG_ALLOCATE_GEOMETRIC);
+	if (ck_bag_init(&bag, b, CK_BAG_ALLOCATE_GEOMETRIC) == false) {
+		fprintf(stderr, "Error: failed ck_bag_init().");
+		exit(EXIT_FAILURE);
+	}
 	fprintf(stderr, "Configuration: %u entries, %zu bytes/block, %zu entries/block\n", writer_max, bag.info.bytes, bag.info.max);
 
 	i = 1;

src/ck_bag.c

@@ -48,7 +48,7 @@ ck_bag_init(struct ck_bag *bag,
 	    size_t n_cachelines,
 	    enum ck_bag_allocation_strategy as)
 {
-	size_t block_overhead;
+	size_t block_overhead, block_size;
 
 	CK_LIST_INIT(&bag->avail_blocks);
 	bag->head = NULL;
@@ -56,19 +56,15 @@ ck_bag_init(struct ck_bag *bag,
 	bag->n_blocks = 0;
 	bag->alloc_strat = as;
 
-	/*
-	 * By default, a ck_bag_block occupies two cachelines. If n_entries is less
-	 * than the # of entries that can fit within one cacheline (including
-	 * overhead), then bag->info.max = number of entries that can fit into a
-	 * single cacheline.
-	 */
 	block_overhead = sizeof(struct ck_bag_block) + allocator_overhead;
 
-	if (n_cachelines == CK_BAG_DEFAULT) {
-		bag->info.max = ((CK_BAG_PAGESIZE - block_overhead) / sizeof(void *));
-	} else {
-		bag->info.max = ((n_cachelines * CK_MD_CACHELINE - block_overhead) / sizeof(void *));
-	}
+	block_size = (n_cachelines == CK_BAG_DEFAULT) ?
+		CK_BAG_PAGESIZE : n_cachelines * CK_MD_CACHELINE;
+
+	if (block_size < block_overhead)
+		return false;
+
+	bag->info.max = (block_size / sizeof(void *));
 
 #ifdef __x86_64__
 	if (bag->info.max > CK_BAG_MAX_N_ENTRIES)