From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
To: Andrea Arcangeli <aarcange@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: [PATCH 2/4] thp: fix MADV_DONTNEED vs. numa balancing race
Date: Thu, 2 Mar 2017 18:10:32 +0300 [thread overview]
Message-ID: <20170302151034.27829-3-kirill.shutemov@linux.intel.com> (raw)
In-Reply-To: <20170302151034.27829-1-kirill.shutemov@linux.intel.com>
In case prot_numa, we are under down_read(mmap_sem). It's critical
to not clear pmd intermittently to avoid race with MADV_DONTNEED
which is also under down_read(mmap_sem):
CPU0: CPU1:
change_huge_pmd(prot_numa=1)
pmdp_huge_get_and_clear_notify()
madvise_dontneed()
zap_pmd_range()
pmd_trans_huge(*pmd) == 0 (without ptl)
// skip the pmd
set_pmd_at();
// pmd is re-established
The race makes MADV_DONTNEED miss the huge pmd and don't clear it
which may break userspace.
Found by code analysis, never saw triggered.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
mm/huge_memory.c | 34 +++++++++++++++++++++++++++++++++-
1 file changed, 33 insertions(+), 1 deletion(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index e7ce73b2b208..bb2b3646bd78 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1744,7 +1744,39 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
if (prot_numa && pmd_protnone(*pmd))
goto unlock;
- entry = pmdp_huge_get_and_clear_notify(mm, addr, pmd);
+ /*
+ * In case prot_numa, we are under down_read(mmap_sem). It's critical
+ * to not clear pmd intermittently to avoid race with MADV_DONTNEED
+ * which is also under down_read(mmap_sem):
+ *
+ * CPU0: CPU1:
+ * change_huge_pmd(prot_numa=1)
+ * pmdp_huge_get_and_clear_notify()
+ * madvise_dontneed()
+ * zap_pmd_range()
+ * pmd_trans_huge(*pmd) == 0 (without ptl)
+ * // skip the pmd
+ * set_pmd_at();
+ * // pmd is re-established
+ *
+ * The race makes MADV_DONTNEED miss the huge pmd and don't clear it
+ * which may break userspace.
+ *
+ * pmdp_invalidate() is required to make sure we don't miss
+ * dirty/young flags set by hardware.
+ */
+ entry = *pmd;
+ pmdp_invalidate(vma, addr, pmd);
+
+ /*
+ * Recover dirty/young flags. It relies on pmdp_invalidate to not
+ * corrupt them.
+ */
+ if (pmd_dirty(*pmd))
+ entry = pmd_mkdirty(entry);
+ if (pmd_young(*pmd))
+ entry = pmd_mkyoung(entry);
+
entry = pmd_modify(entry, newprot);
if (preserve_write)
entry = pmd_mk_savedwrite(entry);
--
2.11.0
--
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next prev parent reply other threads:[~2017-03-02 15:10 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-02 15:10 [PATCH 0/4] thp: fix few MADV_DONTNEED races Kirill A. Shutemov
2017-03-02 15:10 ` [PATCH 1/4] thp: reduce indentation level in change_huge_pmd() Kirill A. Shutemov
2017-04-12 11:37 ` Vlastimil Babka
2017-03-02 15:10 ` Kirill A. Shutemov [this message]
2017-03-03 17:17 ` [PATCH 2/4] thp: fix MADV_DONTNEED vs. numa balancing race Dave Hansen
2017-04-12 13:33 ` Vlastimil Babka
2017-05-16 14:54 ` Vlastimil Babka
2017-05-16 20:29 ` Andrea Arcangeli
2017-05-23 12:42 ` Vlastimil Babka
2017-06-09 8:21 ` Vlastimil Babka
2017-03-02 15:10 ` [PATCH 3/4] thp: fix MADV_DONTNEED vs. MADV_FREE race Kirill A. Shutemov
2017-03-03 5:35 ` Hillf Danton
2017-03-03 10:26 ` Kirill A. Shutemov
2017-03-06 1:44 ` Minchan Kim
2017-03-07 14:04 ` Kirill A. Shutemov
2017-03-08 6:17 ` Minchan Kim
2017-03-06 2:49 ` Aneesh Kumar K.V
2017-03-07 13:52 ` Kirill A. Shutemov
2017-03-02 15:10 ` [PATCH 4/4] thp: fix MADV_DONTNEED vs clear soft dirty race Kirill A. Shutemov
2017-03-03 22:29 ` Andrew Morton
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