Re: [ANNOUNCE] v4.4.3-rt9

From: Thomas Gleixner
Date: Mon Feb 29 2016 - 10:01:45 EST

On Mon, 29 Feb 2016, Mike Galbraith wrote:

> On Mon, 2016-02-29 at 13:46 +0100, Thomas Gleixner wrote:
> > Dear RT folks!
> >
> > I'm pleased to announce the v4.4.3-rt9 patch set. v4.4.2-rt7 and v4.4.3-rt8
> > are non-announced updates to incorporate the linux-4.4.y stable tree.
> >
> > There is one change caused by the 4.4.3 update:
> >
> > The relaxed handling of dump_stack() on RT has been dropped as there is
> > actually a potential deadlock lurking around the corner. See: commit
> > d7ce36924344 upstream. This does not effect the other facilities which
> > gather stack traces.
> Hrm. I had rolled that dropped bit forward as below. I was given
> cause to do a very large pile of ltp oom4 testing (rt kernels will
> livelock due to waitqueue workers waiting for kthreadd to get memory to
> spawn a kworker thread, while stuck kworker holds manager mutex, unless
> workers are run as rt tasks to keep us from getting that depleted in
> the first place), which gives it oodles of exercise, and all _seemed_
> well. Only seemed?

Well, it will work nicely as long as you don't trigger a back trace in hard
irq context. Hmm?