possible to livelock in mprotect() syscall?

Chris Friesen
2003-02-12T19:15:35Z

Is it possible for ksoftirqd to have hold of some resource that other
processes may need to obtain in the mprotect() syscall?

The background for this is as follows:

I've done some work with modifying the linux scheduler to support
additional scheduling classes with limits on cpu percentages available
for each class under stress.

We're hitting a strange scenario under the following conditions:

sched class A is given 90% of the cpu and is based on strict static
priority scheduling

process x is put in sched class A with and is event driven

process y is put in sched class A with a lower priority than x and is a
cpu hog

We would expect to see a background of y running, interrupted by x when
it becomes runnable.

We seem to be seeing a case where process x calls mprotect() and then
blocks while process y runs for large amounts of time. Eventually we
see ksoftirqd run and immediately after that process x wakes up and runs
for a while, but by this time its too late and some timers have expired.

Hence the question--is it possible for ksoftirqd to have hold of some
resource that process x tries to obtain in the mprotect() syscall?

Thanks,

Chris

--
Chris Friesen | MailStop: 043/33/F10
Nortel Networks | work: (613) 765-0557
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