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This commit fixes a system lockup that happens with no system log reporting and affects all Red Hat RT kernels. 

From the commit log:

    Traditionally hrtimer callbacks were run with IRQs disabled, but with
    the introduction of HRTIMER_MODE_SOFT it is possible they run from
    SoftIRQ context, which does _NOT_ have IRQs disabled.
    
    Allow for the CFS bandwidth timers (period_timer and slack_timer) to
    be ran from SoftIRQ context; this entails removing the assumption that
    IRQs are already disabled from the locking.
    
    While mainline doesn't strictly need this, -RT forces all timers not
    explicitly marked with MODE_HARD into MODE_SOFT and trips over this.
    And marking these timers as MODE_HARD doesn't make sense as they're
    not required for RT operation and can potentially be quite expensive.
    
    Reported-by: Tom Putzeys <tom.putzeys.com>
    Tested-by: Mike Galbraith <efault>
    Signed-off-by: Peter Zijlstra (Intel) <peterz>
    Cc: Linus Torvalds <torvalds>
    Cc: Peter Zijlstra <peterz>
    Cc: Sebastian Andrzej Siewior <bigeasy>
    Cc: Thomas Gleixner <tglx>
    Link: https://lkml.kernel.org/r/20190107125231.GE14122@hirez.programming.kicks-ass.net
    Signed-off-by: Ingo Molnar <mingo>

Upstream commit from PREEMPT_RT tree:  c0ad4aa4d8

The code from commit c0ad4aa4d8 got pulled in with other 5.2-rt backports, so this is mainly relevant for pulling back to zstreams

(In reply to Clark Williams from comment #2)
> The code from commit c0ad4aa4d8 got pulled in with other 5.2-rt backports,
> so this is mainly relevant for pulling back to zstreams

kernel-rt-4.18.0-80.5.rt16.1.el8 (2019-03-27) and newer contains this commit

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHSA-2019:3309