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forked fromtorvalds/linux

Commit58ceeb6

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kiryltorvalds
authored andcommitted
thp: fix MADV_DONTNEED vs. MADV_FREE race
Both MADV_DONTNEED and MADV_FREE handled with down_read(mmap_sem).It's critical to not clear pmd intermittently while handling MADV_FREEto 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-establishedIt results in MADV_DONTNEED skipping the pmd, leaving it not cleared.It violates MADV_DONTNEED interface and can result is userspacemisbehaviour.Basically it's the same race as with numa balancing inchange_huge_pmd(), but a bit simpler to mitigate: we don't need topreserve 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.comLink:http://lkml.kernel.org/r/20170302151034.27829-4-kirill.shutemov@linux.intel.comSigned-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>Cc: <stable@vger.kernel.org>Signed-off-by: Andrew Morton <akpm@linux-foundation.org>Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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‎mm/huge_memory.c‎

Lines changed: 1 addition & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1568,8 +1568,7 @@ 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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