[RFC PATCH v5 0/2] Hazard Pointers

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

Here is a v5 of my Hazard Pointers series. I know Boqun has a use case
for it for lockdep.

This new version has those significant changes since v4:

- Fold scheduler integration.
- Actually set ctx slot to backup slot on context switch.
- Remove CONFIG_PREEMPT_HAZPTR config option.
- Use per-cpu ctx pointers for context switch slot tracking
  rather than per-task lists. This accelerates the hazptr
  acquire/release fast-path.
- Guarantee scan forward progress with two-lists scheme.
- Reimplement the hazptr acquire with a temporary wildcard
  to eliminate a dependency on the addr_p load, likely to
  cause a pipeline stall due to the needed memory barrier.
  This simplifies the algorithm, removes the need for pointer
  re-load + comparison, and is expected to be faster on some
  architectures.
- Reduce number of percpu slots to 4, introduce a hazptr_slot_item
  struct to contain both the slot and ctx pointers. Reducing number
  of slots to 4 makes sure all the slot and ctx pointers fit in a
  single cache line.
- Rebased on v7.0-rc1.

Feedback is welcome,

Thanks,

Mathieu

Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: John Stultz <jstultz@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Uladzislau Rezki <urezki@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Zqiang <qiang.zhang1211@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Waiman Long <longman@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: maged.michael@gmail.com
Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc: Jonas Oberhauser <jonas.oberhauser@huaweicloud.com>
Cc: rcu@vger.kernel.org
Cc: linux-mm@kvack.org
Cc: lkmm@lists.linux.dev

Mathieu Desnoyers (2):
  hazptr: Implement Hazard Pointers
  hazptr: Add refscale test

 include/linux/hazptr.h | 197 +++++++++++++++++++++++++++++++++
 init/main.c            |   2 +
 kernel/Makefile        |   2 +-
 kernel/hazptr.c        | 242 +++++++++++++++++++++++++++++++++++++++++
 kernel/rcu/refscale.c  |  43 ++++++++
 kernel/sched/core.c    |   2 +
 6 files changed, 487 insertions(+), 1 deletion(-)
 create mode 100644 include/linux/hazptr.h
 create mode 100644 kernel/hazptr.c

-- 
2.39.5