On Mon, 29 Feb 2016, Mike Galbraith wrote:

On Mon, 2016-02-29 at 13:46 +0100, Thomas Gleixner wrote:

quoted

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?

Thanks,

	tglx