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    SubjectRe: [PATCH] hugetlb: detect race if fail to COW
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    On Sat, Nov 19, 2011 at 3:39 AM, Andrew Morton
    <akpm@linux-foundation.org> wrote:
    > On Fri, 18 Nov 2011 17:11:28 +0100
    > Michal Hocko <mhocko@suse.cz> wrote:
    >
    >> On Fri 18-11-11 23:23:12, Hillf Danton wrote:
    >> > On Fri, Nov 18, 2011 at 11:07 PM, Michal Hocko <mhocko@suse.cz> wrote:
    >> > > On Fri 18-11-11 22:04:37, Hillf Danton wrote:
    >> > >> In the error path that we fail to allocate new huge page, before try again, we
    >> > >> have to check race since page_table_lock is re-acquired.
    >> > >
    >> > > I do not think we can race here because we are serialized by
    >> > > hugetlb_instantiation_mutex AFAIU. Without this lock, however, we could
    >> > > fall into avoidcopy and shortcut despite the fact that other thread has
    >> > > already did the job.
    >> > >
    >> > > The mutex usage is not obvious in hugetlb_cow so maybe we want to be
    >> > > explicit about it (either a comment or do the recheck).
    >> > >
    >> >
    >> > Then the following check is unnecessary, no?
    >>
    >> Hmm, thinking about it some more, I guess we have to recheck because we
    >> can still race with page migration. So we need you patch.
    >>
    >> Reviewed-by: Michal Hocko <mhocko@suse.cz>
    >
    > So we need a new changelog.  How does this look?
    >
    Thanks Andrew and Michal:)

    Best regards
    Hillf
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