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thp: fix MADV_DONTNEED vs. MADV_FREE race
commit 58ceeb6bec
upstream.
Both MADV_DONTNEED and MADV_FREE handled with down_read(mmap_sem).
It's critical to not clear pmd intermittently while handling MADV_FREE
to avoid race with MADV_DONTNEED:
CPU0: CPU1:
madvise_free_huge_pmd()
pmdp_huge_get_and_clear_full()
madvise_dontneed()
zap_pmd_range()
pmd_trans_huge(*pmd) == 0 (without ptl)
// skip the pmd
set_pmd_at();
// pmd is re-established
It results in MADV_DONTNEED skipping the pmd, leaving it not cleared.
It violates MADV_DONTNEED interface and can result is userspace
misbehaviour.
Basically it's the same race as with numa balancing in
change_huge_pmd(), but a bit simpler to mitigate: we don't need to
preserve dirty/young flags here due to MADV_FREE functionality.
[kirill.shutemov@linux.intel.com: Urgh... Power is special again]
Link: http://lkml.kernel.org/r/20170303102636.bhd2zhtpds4mt62a@black.fi.intel.com
Link: http://lkml.kernel.org/r/20170302151034.27829-4-kirill.shutemov@linux.intel.com
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
parent
5ef6f4dec5
commit
f584803c49
1 changed files with 1 additions and 2 deletions
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@ -1380,8 +1380,7 @@ bool madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
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deactivate_page(page);
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if (pmd_young(orig_pmd) || pmd_dirty(orig_pmd)) {
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orig_pmd = pmdp_huge_get_and_clear_full(tlb->mm, addr, pmd,
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tlb->fullmm);
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pmdp_invalidate(vma, addr, pmd);
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orig_pmd = pmd_mkold(orig_pmd);
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orig_pmd = pmd_mkclean(orig_pmd);
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