The patch titled
Subject: thp: reduce indentation level in change_huge_pmd()
has been added to the -mm tree. Its filename is
thp-reduce-indentation-level-in-change_huge_pmd.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/thp-reduce-indentation-level-in-change_huge_pmd.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/thp-reduce-indentation-level-in-change_huge_pmd.patch
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------------------------------------------------------
From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Subject: thp: reduce indentation level in change_huge_pmd()
Patch series "thp: fix few MADV_DONTNEED races"
For MADV_DONTNEED to work properly with huge pages, it's critical to not
clear pmd intermittently unless you hold down_write(mmap_sem). Otherwise
MADV_DONTNEED can miss the THP which can lead to userspace breakage.
See example of such race in commit message of patch 2/4.
All these races are found by code inspection. I haven't seen them
triggered. I don't think it's worth to apply them to stable@.
This patch (of 4):
Restructure code in preparation for a fix.
Link: http://lkml.kernel.org/r/20170302151034.27829-2-kirill.shutemov@xxxxxxxxxxxxxxx
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/huge_memory.c | 56 ++++++++++++++++++++++-----------------------
1 file changed, 28 insertions(+), 28 deletions(-)
diff -puN mm/huge_memory.c~thp-reduce-indentation-level-in-change_huge_pmd mm/huge_memory.c
--- a/mm/huge_memory.c~thp-reduce-indentation-level-in-change_huge_pmd
+++ a/mm/huge_memory.c
@@ -1723,37 +1723,37 @@ int change_huge_pmd(struct vm_area_struc
{
struct mm_struct *mm = vma->vm_mm;
spinlock_t *ptl;
- int ret = 0;
+ pmd_t entry;
+ bool preserve_write;
+ int ret;
ptl = __pmd_trans_huge_lock(pmd, vma);
- if (ptl) {
- pmd_t entry;
- bool preserve_write = prot_numa && pmd_write(*pmd);
- ret = 1;
-
- /*
- * Avoid trapping faults against the zero page. The read-only
- * data is likely to be read-cached on the local CPU and
- * local/remote hits to the zero page are not interesting.
- */
- if (prot_numa && is_huge_zero_pmd(*pmd)) {
- spin_unlock(ptl);
- return ret;
- }
-
- if (!prot_numa || !pmd_protnone(*pmd)) {
- entry = pmdp_huge_get_and_clear_notify(mm, addr, pmd);
- entry = pmd_modify(entry, newprot);
- if (preserve_write)
- entry = pmd_mk_savedwrite(entry);
- ret = HPAGE_PMD_NR;
- set_pmd_at(mm, addr, pmd, entry);
- BUG_ON(vma_is_anonymous(vma) && !preserve_write &&
- pmd_write(entry));
- }
- spin_unlock(ptl);
- }
+ if (!ptl)
+ return 0;
+ preserve_write = prot_numa && pmd_write(*pmd);
+ ret = 1;
+
+ /*
+ * Avoid trapping faults against the zero page. The read-only
+ * data is likely to be read-cached on the local CPU and
+ * local/remote hits to the zero page are not interesting.
+ */
+ if (prot_numa && is_huge_zero_pmd(*pmd))
+ goto unlock;
+
+ if (prot_numa && pmd_protnone(*pmd))
+ goto unlock;
+
+ entry = pmdp_huge_get_and_clear_notify(mm, addr, pmd);
+ entry = pmd_modify(entry, newprot);
+ if (preserve_write)
+ entry = pmd_mk_savedwrite(entry);
+ ret = HPAGE_PMD_NR;
+ set_pmd_at(mm, addr, pmd, entry);
+ BUG_ON(vma_is_anonymous(vma) && !preserve_write && pmd_write(entry));
+unlock:
+ spin_unlock(ptl);
return ret;
}
_
Patches currently in -mm which might be from kirill.shutemov@xxxxxxxxxxxxxxx are
rmap-fix-null-pointer-dereference-on-thp-munlocking.patch
thp-reduce-indentation-level-in-change_huge_pmd.patch
thp-fix-madv_dontneed-vs-numa-balancing-race.patch
thp-fix-madv_dontneed-vs-madv_free-race.patch
thp-fix-madv_dontneed-vs-clear-soft-dirty-race.patch
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