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    SubjectRe: can I bring Linux down by running "renice -20 cpu_intensive_process"?
    Måns Rullgård wrote:

    >Bill Davidsen <davidsen@tmr.com> writes:
    >
    >
    >
    >>Måns Rullgård wrote:
    >>
    >>
    >>>Lee Revell <rlrevell@joe-job.com> writes:
    >>>
    >>>
    >>>
    >>>>On Fri, 2006-03-10 at 22:01 +0000, Måns Rullgård wrote:
    >>>>
    >>>>
    >>>>>Jan Engelhardt <jengelh@linux01.gwdg.de> writes:
    >>>>>
    >>>>>
    >>>>>
    >>>>>>>Subject: can I bring Linux down by running "renice -20
    >>>>>>>cpu_intensive_process"?
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>>>>Depends on what the cpu_intensive_process does. If it tries to
    >>>>>>allocate lots of memory, maybe. If it's _just_ CPU (as in `perl
    >>>>>>-e '1 while 1'`), you get a chance that you can input some
    >>>>>>commands on a terminal to kill it. SCHED_FIFO'ing or
    >>>>>>SCHED_RR'ing such a process is sudden death of course.
    >>>>>>
    >>>>>>
    >>>>>Sysrq+n changes all realtime tasks to normal priority.
    >>>>>
    >>>>>
    >>>>>
    >>>>A nice -20 SCHED_OTHER task is not realtime, only SCHED_FIFO and
    >>>>SCHED_RR.
    >>>>
    >>>>
    >>>Maybe extending sysrq+n to lower the priority of -20 tasks would be a
    >>>good idea.
    >>>
    >>>
    >>>
    >>If it runs before the keyboard thread it doesn't matter...
    >>
    >>
    >
    >Of course not, but that's not generally the case.
    >
    >
    >
    >>But why should this hang anything, when there should be enough i/o
    >>to get out of the user process. There's a good fix for this, don't
    >>give this guy root any more ;-)
    >>
    >>
    >
    >Ever heard of bugs? Anyone developing a program can make a mistake.
    >If the program runs with realtime scheduling a bug that makes it enter
    >an infinite loop (or do something else that hogs the CPU) can be
    >difficult to find since it rather efficiently locks you out.
    >
    >
    >
    Please google "emoticons" and find out what those funny characters at
    the end of the of the paragraph you quoted really mean. Sheesh!

    --
    bill davidsen <davidsen@tmr.com>
    CTO TMR Associates, Inc
    Doing interesting things with small computers since 1979

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