mm/vmalloc.c: fix potential memory leak

In VM_MAP_PUT_PAGES case, we should put pages and free array in vfree.
But we missed to set area->nr_pages in vmap().  So we would fail to put
pages in __vunmap() because area->nr_pages = 0.

Link: https://lkml.kernel.org/r/20210107123541.39206-1-linmiaohe@huawei.com
Fixes: b944afc9 ("mm: add a VM_MAP_PUT_PAGES flag for vmap")
Signed-off-by: Shijie Luo <luoshijie1@huawei.com>
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/vmalloc.c

@@ -2420,8 +2420,10 @@ void *vmap(struct page **pages, unsigned int count,
 		return NULL;
 	}
 
-	if (flags & VM_MAP_PUT_PAGES)
+	if (flags & VM_MAP_PUT_PAGES) {
 		area->pages = pages;
+		area->nr_pages = count;
+	}
 	return area->addr;
 }
 EXPORT_SYMBOL(vmap);