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    SubjectRe: /proc/sys/kernel/pid_max issues
    On Mon, 2004-09-13 at 03:57, Ingo Molnar wrote:
    >> this is a pretty sweeping assertion. Would you
    >> care to mention a few examples of such hazards?

    On Mon, Sep 13, 2004 at 09:54:09AM -0400, Albert Cahalan wrote:
    > kill(12345,9)
    > setpriority(PRIO_PROCESS,12345,-20)
    > sched_setscheduler(12345, SCHED_FIFO, &sp)
    > Prior to the call being handled, the process may
    > die and be replaced. Some random innocent process,
    > or a not-so-innocent one, will get acted upon by
    > mistake. This is broken and dangerous.
    > Well, it's in the UNIX standard. The best one can
    > do is to make the race window hard to hit, with LRU.

    How do you propose to queue pid's? This is space constrained. I don't
    believe it's feasible and/or desirable to attempt this, as there are
    4 million objects to track independent of machine size. The general
    tactic of cyclic order allocation is oriented toward making this rare
    and/or hard to trigger by having a reuse period long enough that what
    processes there are after a pid wrap are likely to have near-indefinite
    lifetimes. i.e. it's the closest feasible approximation of LRU. If you
    truly want/need reuse to be gone, 64-bit+ pid's are likely best.

    -- wli
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