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    SubjectRe: [PATCH] Mark timer_stats as incompatible with multiple pid namespaces

    * Eric W. Biederman <ebiederm@xmission.com> wrote:

    > > What the heck??? Please solve this properly instead of hiding it.
    > > /proc/timer_stats is damn useful and it's a must-have for powertop
    > > to work.
    >
    > Hmm. Perhaps the dependency conflict should go in the other direction
    > then.
    >
    > My goal is to document the issue while a proper fix is being written.
    > I have known about this for all of about 1 day now. It was added
    > since last time I went through the kernel and made a thorough sweep of
    > pid users.
    >
    > What the proper fix is isn't even obvious at this point. Possibly it
    > is making /proc/timer_stats disappear in child pid namespaces.
    > Which we don't currently have the infrastructure fore.
    >
    > Possibly it is reworking the stats collection so we store a struct pid
    > * instead of a pid_t value. So we would know if the reader of the
    > value can even see processes you have collected stats for.

    the problem is, this interface stores historic PIDs too - i.e. PIDs of
    tasks that might have exited already.

    the proper way would be to also store the namespace address, and to
    filter out non-matching entries. (If leakage of this data across
    namespace creation is of any concern then flush out existing namespace
    data when a namespace is destroyed)

    Ingo


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