Hi Peter, This is a follow-up for Lyude's work [1]. After learning the current preempt_count() usage and how ARM64 handle this, I came up with this series that could resolve your feedback [2]. The basic idea is based on:
1) preempt_count() previously already masks our NEED_RESCHED bit, so the effective bits is 31bits 2) with a 64bit preempt count implementation (as in your PREEMPT_LONG proposal), the effective bits that record "whether we CAN preempt or not" still fit in 32bit (i.e. an int) as a result, I don't think we need to change the existing preempt_count() API, but rather keep "32bit vs 64bit" as an implementation detail. This saves us the need to change the printk code for preempt_count(). v1: https://lore.kernel.org/rust-for-linux/[email protected]/ Changes since v1: * Rename PREEMPT_COUNT_64BIT to HAS_SEPARATE_PREEMPT_RESCHED_BITS per Mark Rutland. * Add s390's support for HAS_SEPARATE_PREEMPT_RESCHED_BITS for Heiko Carstens, thank you! * Reorder patch #1 and #2 per Steven Rostedt. * Keep the NMI count warning per Steven Rostedt and Joel Fernandes. * Fix an race between interrupt disabling and softirq reported by sashiko (see the changes in __irq_exit_rcu()). * Add Context Analysis annotations for the newly introduced API. * Sync the preempt bits changes to BPF tests. I would like to target this changes for 7.2 if possible. [1]: https://lore.kernel.org/all/[email protected]/ [2]: https://lore.kernel.org/all/[email protected]/ Regards, Boqun Boqun Feng (8): preempt: Introduce HARDIRQ_DISABLE_BITS preempt: Introduce __preempt_count_{sub, add}_return() irq & spin_lock: Add counted interrupt disabling/enabling locking: Switch to _irq_{disable,enable}() variants in cleanup guards sched: Remove the unused preempt_offset parameter of __cant_sleep() sched: Avoid signed comparison of preempt_count() in __cant_migrate() preempt: Introduce HAS_SEPARATE_PREEMPT_RESCHED_BITS arm64: sched/preempt: Enable HAS_SEPARATE_PREEMPT_RESCHED_BITS Heiko Carstens (1): s390/preempt: Enable HAS_SEPARATE_PREEMPT_RESCHED_BITS Joel Fernandes (1): preempt: Track NMI nesting to separate per-CPU counter Lyude Paul (2): openrisc: Include <linux/cpumask.h> in smp.h irq: Add KUnit test for refcounted interrupt enable/disable arch/arm64/Kconfig | 1 + arch/arm64/include/asm/preempt.h | 18 +++ arch/openrisc/include/asm/smp.h | 2 + arch/s390/Kconfig | 1 + arch/s390/include/asm/lowcore.h | 13 ++- arch/s390/include/asm/preempt.h | 49 ++++---- arch/x86/Kconfig | 1 + arch/x86/include/asm/preempt.h | 61 +++++++--- arch/x86/kernel/cpu/common.c | 2 +- include/asm-generic/preempt.h | 14 +++ include/linux/hardirq.h | 43 ++++++- include/linux/interrupt_rc.h | 65 +++++++++++ include/linux/kernel.h | 4 +- include/linux/preempt.h | 35 ++++-- include/linux/spinlock.h | 48 +++++--- include/linux/spinlock_api_smp.h | 41 +++++++ include/linux/spinlock_api_up.h | 16 +++ include/linux/spinlock_rt.h | 18 +++ kernel/Kconfig.preempt | 4 + kernel/irq/Makefile | 1 + kernel/irq/refcount_interrupt_test.c | 109 ++++++++++++++++++ kernel/locking/spinlock.c | 29 +++++ kernel/sched/core.c | 18 ++- kernel/softirq.c | 22 +++- lib/locking-selftest.c | 2 +- .../testing/selftests/bpf/bpf_experimental.h | 7 +- 26 files changed, 544 insertions(+), 80 deletions(-) create mode 100644 include/linux/interrupt_rc.h create mode 100644 kernel/irq/refcount_interrupt_test.c -- 2.50.1 (Apple Git-155)
