Subject: Re: [linux-audio-dev] [SOURCE] rt monitor to kill runaway RT processes
From: rm (async_AT_cc.gatech.edu)
Date: Wed Aug 28 2002 - 19:47:41 EEST
On Wed, Aug 28, 2002 at 10:15:54AM -0400, Paul Davis wrote:
> a side note: JACK, when run in RT mode, launches its own maximal
> priority thread to perform exactly this function. all other RT threads
> run at lower priorities. i believe that it is not possible to use JACK
> to perform DOS attacks like this unless the client modifies its
> scheduling priority itself.
which is still an issue. relying on the courtesy of user programs is
probably not optimal (as i'm sure you're all well aware).
this issue bugs me especially because people go on and on about the
stability of *nix, and yet here we have an easy way in which a user
(albeit root) program can bring the system to its knees. all it takes
is one small bug in a reasonably complex program--not exactly
uncommon.
i've been working on a kernel patch that will allow a program to use
the entire cpu up to some percentage of cycles which are reserved.
(this is a common approach in RT literature). preliminary testing
seems to indicate its workable, but a number of issues need to be
cleared up (>1 cpu, what happens if more than one process wants fifo
scheduling, etc). i will probably add a new scheduling policy,
something like SCHED_USER_FIFO.
anyway hopefully soonish i will get a chance to swap it in and make a
patch if anyone is interested. (if lots of folks are interested i'll
get to it sooner rather than later if possible).
if anyone has thoughts feel free to share.
rob
----
Robert Melby
Georgia Institute of Technology, Atlanta Georgia, 30332
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