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

[Bill Davidsen <davidsen@tmr.com>]

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