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    SubjectRe: [PATCH v2] mm/page_isolation: fix potential missing call to unset_migratetype_isolate()
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    On 2021/9/13 20:59, Michal Hocko wrote:
    > On Mon 13-09-21 20:43:35, Miaohe Lin wrote:
    >> On 2021/9/13 20:20, David Hildenbrand wrote:
    >>> On 13.09.21 14:12, Michal Hocko wrote:
    >>>> On Mon 13-09-21 19:51:25, Miaohe Lin wrote:
    >>>>> In start_isolate_page_range() undo path, pfn_to_online_page() just checks
    >>>>> the first pfn in a pageblock while __first_valid_page() will traverse the
    >>>>> pageblock until the first online pfn is found. So we may miss the call to
    >>>>> unset_migratetype_isolate() in undo path and pages will remain isolated
    >>>>> unexpectedly. Fix this by calling undo_isolate_page_range() and this will
    >>>>> also help to simplify the code further.
    >>>>
    >>>> I like the clean up part but is this a real problem that requires CC
    >>>> stable? Have you ever seen this to be a real problem? It looks like
    >>>> something based on reading the code.
    >>
    >> I'm sorry but I haven't seen this to be a real problem. It's a theoretical bug.
    >
    > Make it clear in the changelog

    Will do.

    >
    >>> We discussed that it isn't an issue anymore (we never call it on
    >>> memory holes), but might have been an issue on older kernels, back
    >>> when we didn't have the "memory holes" check in the memory offlining
    >>> path in place.
    >>
    >> So is the Cc:stable needed in this case?
    >
    > I do not think so. Even if this was happening in the practice then the
    > practical consequences would be pretty minor, right? (few pageblocks
    > stay isolated thus unavailable).
    >
    > I do realize that the stable tree is in a hoarding mode for quite some
    > years but my general approach has been (in line with the documentation)
    > to mark and backport only fixes that really do matter.

    So even the Fixes tag should be removed ?

    Many thanks.

    >

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