mm/hugetlb: avoid hardcoding while checking if cma is enabled

hugetlb_cma[0] can be NULL due to various reasons, for example, node0
has no memory.  so NULL hugetlb_cma[0] doesn't necessarily mean cma is
not enabled.  gigantic pages might have been reserved on other nodes.
This patch fixes possible double reservation and CMA leak.

[akpm@linux-foundation.org: fix CONFIG_CMA=n warning]
[sfr@canb.auug.org.au: better checks before using hugetlb_cma]
  Link: http://lkml.kernel.org/r/20200721205716.6dbaa56b@canb.auug.org.au

Fixes: cf11e85fc0 ("mm: hugetlb: optionally allocate gigantic hugepages using cma")
Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Acked-by: Roman Gushchin <guro@fb.com>
Cc: Jonathan Cameron <jonathan.cameron@huawei.com>
Cc: <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/20200710005726.36068-1-song.bao.hua@hisilicon.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/hugetlb.c

@@ -45,7 +45,10 @@ int hugetlb_max_hstate __read_mostly;
 unsigned int default_hstate_idx;
 struct hstate hstates[HUGE_MAX_HSTATE];
 
+#ifdef CONFIG_CMA
 static struct cma *hugetlb_cma[MAX_NUMNODES];
+#endif
+static unsigned long hugetlb_cma_size __initdata;
 
 /*
  * Minimum page order among possible hugepage sizes, set to a proper value
@@ -1235,9 +1238,10 @@ static void free_gigantic_page(struct page *page, unsigned int order)
 	 * If the page isn't allocated using the cma allocator,
 	 * cma_release() returns false.
 	 */
-	if (IS_ENABLED(CONFIG_CMA) &&
-	    cma_release(hugetlb_cma[page_to_nid(page)], page, 1 << order))
+#ifdef CONFIG_CMA
+	if (cma_release(hugetlb_cma[page_to_nid(page)], page, 1 << order))
 		return;
+#endif
 
 	free_contig_range(page_to_pfn(page), 1 << order);
 }
@@ -1248,7 +1252,8 @@ static struct page *alloc_gigantic_page(struct hstate *h, gfp_t gfp_mask,
 {
 	unsigned long nr_pages = 1UL << huge_page_order(h);
 
-	if (IS_ENABLED(CONFIG_CMA)) {
+#ifdef CONFIG_CMA
+	{
 		struct page *page;
 		int node;
 
@@ -1262,6 +1267,7 @@ static struct page *alloc_gigantic_page(struct hstate *h, gfp_t gfp_mask,
 				return page;
 		}
 	}
+#endif
 
 	return alloc_contig_pages(nr_pages, gfp_mask, nid, nodemask);
 }
@@ -2571,7 +2577,7 @@ static void __init hugetlb_hstate_alloc_pages(struct hstate *h)
 
 	for (i = 0; i < h->max_huge_pages; ++i) {
 		if (hstate_is_gigantic(h)) {
-			if (IS_ENABLED(CONFIG_CMA) && hugetlb_cma[0]) {
+			if (hugetlb_cma_size) {
 				pr_warn_once("HugeTLB: hugetlb_cma is enabled, skip boot time allocation\n");
 				break;
 			}
@@ -5654,7 +5660,6 @@ void move_hugetlb_state(struct page *oldpage, struct page *newpage, int reason)
 }
 
 #ifdef CONFIG_CMA
-static unsigned long hugetlb_cma_size __initdata;
 static bool cma_reserve_called __initdata;
 
 static int __init cmdline_parse_hugetlb_cma(char *p)