Re: [PATCH] fix __mod_timer vs __run_timers deadlock.

Benjamin Herrenschmidt
2005-05-03T01:31:53Z

On Mon, 2005-05-02 at 21:24 -0400, Lee Revell wrote:
> On Tue, 2005-05-03 at 10:13 +1000, Benjamin Herrenschmidt wrote:
> > Well, there may be other issues brought by this new timer code though.
> > I'm running G5s regulary without a lockup or anything for weeks, so it
> > would be interesting if you could try to find out what's involved in
> > that other lockup you had.
>
> It seems like it would not be to hard to create a timer test suite that
> just hammers the timer subsystem, creating and deleting and modifying
> zillions of timers, changing the system time, etc. Combined with
> running with HZ=10000 or something it seems like you could shake out
> bugs a lot faster than just running & waiting for a race to show up.

Well, yes and know... the timer subsytem is very senstivie to things
like memory barriers issues, and thus changes in the "barrier" semantics
of a timer call may have an impact on the caller code regardless of the
validity of the timer code itself, that sort of thing ...

> I've seen timer related issues (the set_rtc_mmss issue that George
> Anzinger fixed) while testing the RT patchset that I could only ever
> reproduce once.