[PATCH 00/11] rcu: introduce percpu rcu_preempt_depth

[Lai Jiangshan]

My mind was occupied with percpu rcu_preempt_depth for
several years since Peter introduced percu preempt_count.
But it was stopped by no good way to avoid the scheduler deadlocks.
Now we have deferred_qs to avoid the deadlocks, it is time to implement it.

During the work, I found two possible? drawbacks (fixed by patch1/2
but patch2 is reverted by patch8 which is a better way).

And my not noticing the order of handling special.b.deferred_qs
ate many debuging energy (patch7).

The percpu rcu_preempt_depth patch is the last patch, patch11.

x86 is the only beneficial arch. But other arch can put
->rcu_read_lock_nesting and ->rcu_read_unlock_special to
thread_info to avoid the function call after we have patch8/9.

CC: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CC: Ingo Molnar <mingo@xxxxxxxxxx>
CC: "H. Peter Anvin" <hpa@xxxxxxxxx>
CC: x86@xxxxxxxxxx
CC: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
CC: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
CC: Steven Rostedt <rostedt@xxxxxxxxxxx>
CC: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
CC: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
CC: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CC: linux-kernel@xxxxxxxxxxxxxxx
CC: rcu@xxxxxxxxxxxxxxx

Lai Jiangshan (11):
  rcu: avoid leaking exp_deferred_qs into next GP
  rcu: fix bug when rcu_exp_handler() in nested interrupt
  rcu: clean up rcu_preempt_deferred_qs_irqrestore()
  rcu: cleanup rcu_preempt_deferred_qs()
  rcu: clean all rcu_read_unlock_special after report qs
  rcu: clear t->rcu_read_unlock_special in one go
  rcu: set special.b.deferred_qs before wake_up()
  rcu: don't use negative ->rcu_read_lock_nesting
  rcu: wrap usages of rcu_read_lock_nesting
  rcu: clear the special.b.need_qs in rcu_note_context_switch()
  x86,rcu: use percpu rcu_preempt_depth

 arch/x86/Kconfig                         |   2 +
 arch/x86/include/asm/rcu_preempt_depth.h |  87 +++++++++++++++
 arch/x86/kernel/cpu/common.c             |   7 ++
 arch/x86/kernel/process_32.c             |   2 +
 arch/x86/kernel/process_64.c             |   2 +
 include/linux/rcupdate.h                 |  24 +++++
 init/init_task.c                         |   2 +-
 kernel/fork.c                            |   2 +-
 kernel/rcu/Kconfig                       |   3 +
 kernel/rcu/tree_exp.h                    |  58 ++++------
 kernel/rcu/tree_plugin.h                 | 130 +++++++++++++----------
 11 files changed, 220 insertions(+), 99 deletions(-)
 create mode 100644 arch/x86/include/asm/rcu_preempt_depth.h

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2.20.1