• David Gibson's avatar
    [PATCH] hugepage: Fix hugepage logic in free_pgtables() · 9da61aef
    David Gibson authored
    free_pgtables() has special logic to call hugetlb_free_pgd_range() instead
    of the normal free_pgd_range() on hugepage VMAs.  However, the test it uses
    to do so is incorrect: it calls is_hugepage_only_range on a hugepage sized
    range at the start of the vma.  is_hugepage_only_range() will return true
    if the given range has any intersection with a hugepage address region, and
    in this case the given region need not be hugepage aligned.  So, for
    example, this test can return true if called on, say, a 4k VMA immediately
    preceding a (nicely aligned) hugepage VMA.
    At present we get away with this because the powerpc version of
    hugetlb_free_pgd_range() is just a call to free_pgd_range().  On ia64 (the
    only other arch with a non-trivial is_hugepage_only_range()) we get away
    with it for a different reason; the hugepage area is not contiguous with
    the rest of the user address space, and VMAs are not permitted in between,
    so the test can't return a false positive there.
    Nonetheless this should be fixed.  We do that in the patch below by
    replacing the is_hugepage_only_range() test with an explicit test of the
    VMA using is_vm_hugetlb_page().
    This in turn changes behaviour for platforms where is_hugepage_only_range()
    returns false always (everything except powerpc and ia64).  We address this
    by ensuring that hugetlb_free_pgd_range() is defined to be identical to
    free_pgd_range() (instead of a no-op) on everything except ia64.  Even so,
    it will prevent some otherwise possible coalescing of calls down to
    free_pgd_range().  Since this only happens for hugepage VMAs, removing this
    small optimization seems unlikely to cause any trouble.
    This patch causes no regressions on the libhugetlbfs testsuite - ppc64
    POWER5 (8-way), ppc64 G5 (2-way) and i386 Pentium M (UP).
    Signed-off-by: default avatarDavid Gibson <dwg@au1.ibm.com>
    Cc: William Lee Irwin III <wli@holomorphy.com>
    Acked-by: default avatarHugh Dickins <hugh@veritas.com>
    Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>