Re: can I bring Linux down by running "renice -20 cpu_intensive_process"?

[Måns Rullgård]

Bill Davidsen <davidsen@xxxxxxx> writes:

> Måns Rullgård wrote:
>> Lee Revell <rlrevell@xxxxxxxxxxx> writes:
>>
>>> On Fri, 2006-03-10 at 22:01 +0000, Måns Rullgård wrote:
>>>> Jan Engelhardt <jengelh@xxxxxxxxxxxxxxx> 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.

-- 
Måns Rullgård
mru@xxxxxxxxxxxxx
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