linux-kernel - [PATCH] mm/migrate: Fix early increment of migrate->npages

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Date:   Mon,  2 Oct 2017 16:44:02 -0500
From:   Reza Arbab <arbab@...ux.vnet.ibm.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Jérôme Glisse <jglisse@...hat.com>
Cc:     Balbir Singh <bsingharora@...il.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Minchan Kim <minchan@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH] mm/migrate: Fix early increment of migrate->npages

The intention here is to set the same array element in src and dst.
Switch the order of these lines so that migrate->npages is only
incremented after we've used it.

Fixes: 8315ada7f095 ("mm/migrate: allow migrate_vma() to alloc new page on empty entry")
Cc: Jérôme Glisse <jglisse@...hat.com>
Signed-off-by: Reza Arbab <arbab@...ux.vnet.ibm.com>
---
 mm/migrate.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index dea0ceb..c4546cc 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2146,8 +2146,8 @@ static int migrate_vma_collect_hole(unsigned long start,
 	unsigned long addr;
 
 	for (addr = start & PAGE_MASK; addr < end; addr += PAGE_SIZE) {
-		migrate->src[migrate->npages++] = MIGRATE_PFN_MIGRATE;
 		migrate->dst[migrate->npages] = 0;
+		migrate->src[migrate->npages++] = MIGRATE_PFN_MIGRATE;
 		migrate->cpages++;
 	}
 
-- 
1.8.3.1