linux-kernel - [PATCH v2] sparc64: Fix gup_huge

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Date:   Thu, 22 Jun 2017 17:15:08 -0700
From:   Nitin Gupta <nitin.m.gupta@...cle.com>
To:     "David S. Miller" <davem@...emloft.net>
Cc:     Julian Calaby <julian.calaby@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Nitin Gupta <nitin.m.gupta@...cle.com>,
        Lorenzo Stoakes <lstoakes@...il.com>, Jan Kara <jack@...e.cz>,
        Michal Hocko <mhocko@...e.com>, sparclinux@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2] sparc64: Fix gup_huge_pmd

The function assumes that each PMD points to head of a
huge page. This is not correct as a PMD can point to
start of any 8M region with a, say 256M, hugepage. The
fix ensures that it points to the correct head of any PMD
huge page.

Cc: Julian Calaby <julian.calaby@...il.com>
Signed-off-by: Nitin Gupta <nitin.m.gupta@...cle.com>
---
 Changes since v1
 - Clarify use of 'head' variable (Julian Calaby)

 arch/sparc/mm/gup.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/sparc/mm/gup.c b/arch/sparc/mm/gup.c
index cd0e32b..f80cfc6 100644
--- a/arch/sparc/mm/gup.c
+++ b/arch/sparc/mm/gup.c
@@ -78,8 +78,8 @@ static int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
 		return 0;
 
 	refs = 0;
-	head = pmd_page(pmd);
-	page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
+	page = pmd_page(pmd) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
+	head = compound_head(page);
 	do {
 		VM_BUG_ON(compound_head(page) != head);
 		pages[*nr] = page;
-- 
2.9.2