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    SubjectRe: [PATCH 1/2] perf: Add closing sibling events' file descriptors
    Date
    Andi Kleen <ak@linux.intel.com> writes:

    >> > This adds an opt-in flag to the perf_event_open() syscall to retain
    >> > sibling events after their file descriptors are closed. In this case, the
    >> > actual events will be closed with the group leader.
    >>
    >> So having the 1:1 relation with filedesc imposes a resource limit on
    >> userspace.
    >>
    >> This patch breaks that and enables a user to basically DoS the system by
    >> creating unbound events.
    >
    > The idea was to account the events in the locked memory allocation too.
    > Not sure that made it into the patch though.

    It didn't. I can't figure out what to charge on the locked memory, as
    all that memory is in kernel-side objects. It also needs to make sense
    as iirc the default MLOCK_LIMIT is quite low, you'd hit it sooner than
    the file descriptor limit.

    > It has a minor issue that it might break some existing setups that rely
    > on the mmap fitting exactly into the mmap allocation, but that could
    > be solved by allowing a little slack, since the existing setups
    > likely don't have that many events.

    I don't see how to make this work in a sane way. Besides, if we have to
    have a limit anyway, sticking with the existing one is just easier and
    1:1 is kind of more logical.

    Regards,
    --
    Alex

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