linux-kernel - [PATCH] shmem: Fix link error if huge pages support is disabled

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Date:	Wed,  3 Aug 2016 19:58:19 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: [PATCH] shmem: Fix link error if huge pages support is disabled

If CONFIG_TRANSPARENT_HUGE_PAGECACHE=n, HPAGE_PMD_NR evaluates to
BUILD_BUG_ON(), and may cause (e.g. with gcc 4.12):

    mm/built-in.o: In function `shmem_alloc_hugepage':
    shmem.c:(.text+0x17570): undefined reference to `__compiletime_assert_1365'

To fix this, move the assignment to hindex after the check for huge
pages support.

Fixes: 800d8c63b2e989c2 ("shmem: add huge pages support")
Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
---
 mm/shmem.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 2ac19a61d5655b82..7f7748a0f9e1f738 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1362,13 +1362,14 @@ static struct page *shmem_alloc_hugepage(gfp_t gfp,
 	struct vm_area_struct pvma;
 	struct inode *inode = &info->vfs_inode;
 	struct address_space *mapping = inode->i_mapping;
-	pgoff_t idx, hindex = round_down(index, HPAGE_PMD_NR);
+	pgoff_t idx, hindex;
 	void __rcu **results;
 	struct page *page;
 
 	if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE))
 		return NULL;
 
+	hindex = round_down(index, HPAGE_PMD_NR);
 	rcu_read_lock();
 	if (radix_tree_gang_lookup_slot(&mapping->page_tree, &results, &idx,
 				hindex, 1) && idx < hindex + HPAGE_PMD_NR) {
-- 
1.9.1