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

[Bill Davidsen]

Måns Rullgård wrote:

> 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.
>
>  
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@xxxxxxx>
 CTO TMR Associates, Inc
 Doing interesting things with small computers since 1979

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