RCU CPU stall warning updates for v4.15

Hello!

This series updates RCU CPU stall warnings, and also, due to conflicts, pulls along a long-standing patch that allows cond_resched() to do the work that cond_resched_rcu_qs() does.

1. Make cond_resched() provide RCU quiescent state. This has been
heavily optimized over its lifetime, which is almost one year. It should be close enough. Yes, some benchmarks show that it results in higher context-switch rates, but then again, the problem being solved is in fact too few context switches. ;-)

2. Make RCU CPU stall warnings check for irq-disabled CPUs.

3. Turn off tracing before dumping traces.

4. Suppress RCU CPU stall warnings while dumping RCU-related traces.

Thanx, Paul

------------------------------------------------------------------------

 include/linux/sched.h    |    3 -
 kernel/rcu/rcu.h         |   21 +++++++
 kernel/rcu/tree.c        |  129 +++++++++++++++++++++++++++++++++++------------
 kernel/rcu/tree.h        |    5 +
 kernel/rcu/tree_plugin.h |    7 ++
 kernel/rcu/update.c      |    1 
 kernel/sched/core.c      |    1 
 7 files changed, 132 insertions(+), 35 deletions(-)