Re: [ANNOUNCE] v4.4.3-rt9

[Mike Galbraith]

On Mon, 2016-02-29 at 16:00 +0100, Thomas Gleixner wrote:
> 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?

Poo.. that's a pretty darn good reason.  Thanks.

	-Mike