linux-kernel - [PATCH] mm: migration: deposit page table when copying a PMD migration entry.

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Date:   Mon, 30 Oct 2017 10:46:36 -0400
From:   Zi Yan <zi.yan@...t.com>
To:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Zi Yan <zi.yan@...rutgers.edu>,
        Fengguang Wu <fengguang.wu@...el.com>
Subject: [PATCH] mm: migration: deposit page table when copying a PMD migration entry.

From: Zi Yan <zi.yan@...rutgers.edu>

We need to deposit pre-allocated PTE page table when a PMD migration
entry is copied in copy_huge_pmd(). Otherwise, we will leak the
pre-allocated page and cause a NULL pointer dereference later
in zap_huge_pmd().

The missing counters during PMD migration entry copy process are added
as well.

The bug report is here: https://lkml.org/lkml/2017/10/29/214

Fixes: 84c3fc4e9c563 ("mm: thp: check pmd migration entry in common path")
Reported-by: Fengguang Wu <fengguang.wu@...el.com>
Signed-off-by: Zi Yan <zi.yan@...rutgers.edu>
Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
---
 mm/huge_memory.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 269b5df58543..1981ed697dab 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -941,6 +941,9 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 				pmd = pmd_swp_mksoft_dirty(pmd);
 			set_pmd_at(src_mm, addr, src_pmd, pmd);
 		}
+		add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
+		atomic_long_inc(&dst_mm->nr_ptes);
+		pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);
 		set_pmd_at(dst_mm, addr, dst_pmd, pmd);
 		ret = 0;
 		goto out_unlock;
-- 
2.14.2