Hi, Here is a revisited version of my Hazard Pointers series. Boqun, Joel, if you guys have time to try it out with your use-cases it would be great!
This new version does the following: - It has 8 preallocated hazard pointer slots per CPU (one cache line), - The hazard pointer user allocates a hazard pointer context variable (typically on the stack), which contains the pointer to the slot *and* a backup slot, - When all the per-CPU slots are in use, fallback to the backup slot. Chain the backup slot into per-CPU lists, each protected by a raw spinlock. - The hazard pointer synchronize does a piecewise iteration on the per-CPU overflow slots lists, releasing the raw spinlock between each list item. It uses a 64-bit generation counter to check for concurrent list changes, and restart the traversal on generation counter mismatch. - There is a new CONFIG_PREEMPT_HAZPTR config option. When enabled, the hazard pointer acquire/release adds and then removes the hazard pointer context from a per-task linked list. On context switch, the scheduler migrates the per-CPU slots used by the task to the backup per-context slots, thus making sure the per-CPU slots are not used by preempted and blocked tasks. It is based on v6.18.1. Review is very welcome, Thanks, Mathieu Cc: Nicholas Piggin <[email protected]> Cc: Michael Ellerman <[email protected]> Cc: Greg Kroah-Hartman <[email protected]> Cc: Sebastian Andrzej Siewior <[email protected]> Cc: "Paul E. McKenney" <[email protected]> Cc: Will Deacon <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Boqun Feng <[email protected]> Cc: Alan Stern <[email protected]> Cc: John Stultz <[email protected]> Cc: Neeraj Upadhyay <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Andrew Morton <[email protected]> Cc: Boqun Feng <[email protected]> Cc: Frederic Weisbecker <[email protected]> Cc: Joel Fernandes <[email protected]> Cc: Josh Triplett <[email protected]> Cc: Uladzislau Rezki <[email protected]> Cc: Steven Rostedt <[email protected]> Cc: Lai Jiangshan <[email protected]> Cc: Zqiang <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Waiman Long <[email protected]> Cc: Mark Rutland <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Vlastimil Babka <[email protected]> Cc: [email protected] Cc: Mateusz Guzik <[email protected]> Cc: Jonas Oberhauser <[email protected]> Cc: [email protected] Cc: [email protected] Cc: [email protected] Mathieu Desnoyers (4): compiler.h: Introduce ptr_eq() to preserve address dependency Documentation: RCU: Refer to ptr_eq() hazptr: Implement Hazard Pointers hazptr: Migrate per-CPU slots to backup slot on context switch Documentation/RCU/rcu_dereference.rst | 38 +++- include/linux/compiler.h | 63 +++++++ include/linux/hazptr.h | 241 ++++++++++++++++++++++++++ include/linux/sched.h | 4 + init/init_task.c | 3 + init/main.c | 2 + kernel/Kconfig.preempt | 10 ++ kernel/Makefile | 2 +- kernel/fork.c | 3 + kernel/hazptr.c | 150 ++++++++++++++++ kernel/sched/core.c | 2 + 11 files changed, 512 insertions(+), 6 deletions(-) create mode 100644 include/linux/hazptr.h create mode 100644 kernel/hazptr.c -- 2.39.5
