On Fri, Oct 04, 2024 at 02:27:33PM -0400, Mathieu Desnoyers wrote:
> include/linux/hp.h | 158 +++++++++++++++++++++++++++++++++++++++++++++
> kernel/Makefile | 2 +-
> kernel/hp.c | 46 +++++++++++++
> 3 files changed, 205 insertions(+), 1 deletion(-)
> create mode 100644 include/linux/hp.h
> create mode 100644 kernel/hp.c
>
> diff --git a/include/linux/hp.h b/include/linux/hp.h
> new file mode 100644
> index 000000000000..e85fc4365ea2
> --- /dev/null
> +++ b/include/linux/hp.h
> @@ -0,0 +1,158 @@
> +// SPDX-FileCopyrightText: 2024 Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> +//
> +// SPDX-License-Identifier: LGPL-2.1-or-later
> +
> +#ifndef _LINUX_HP_H
> +#define _LINUX_HP_H
> +
> +/*
> + * HP: Hazard Pointers
> + *
> + * This API provides existence guarantees of objects through hazard
> + * pointers.
> + *
> + * It uses a fixed number of hazard pointer slots (nr_cpus) across the
> + * entire system for each HP domain.
> + *
> + * Its main benefit over RCU is that it allows fast reclaim of
> + * HP-protected pointers without needing to wait for a grace period.
> + *
> + * It also allows the hazard pointer scan to call a user-defined callback
> + * to retire a hazard pointer slot immediately if needed. This callback
> + * may, for instance, issue an IPI to the relevant CPU.
> + *
> + * References:
> + *
> + * [1]: M. M. Michael, "Hazard pointers: safe memory reclamation for
> + * lock-free objects," in IEEE Transactions on Parallel and
> + * Distributed Systems, vol. 15, no. 6, pp. 491-504, June 2004
> + */
> +
> +#include <linux/rcupdate.h>
> +
> +/*
> + * Hazard pointer slot.
> + */
> +struct hp_slot {
> + void *addr;
> +};
> +
> +/*
> + * Hazard pointer context, returned by hp_use().
> + */
> +struct hp_ctx {
> + struct hp_slot *slot;
> + void *addr;
> +};
> +
> +/*
> + * hp_scan: Scan hazard pointer domain for @addr.
> + *
> + * Scan hazard pointer domain for @addr.
> + * If @retire_cb is NULL, wait to observe that each slot contains a value
> + * that differs from @addr.
> + * If @retire_cb is non-NULL, invoke @callback for each slot containing
> + * @addr.
> + */
> +void hp_scan(struct hp_slot __percpu *percpu_slots, void *addr,
> + void (*retire_cb)(int cpu, struct hp_slot *slot, void *addr));
struct hp_domain {
struct hp_slot __percpu *slots
};
might clarify things a wee little.
> +
> +/* Get the hazard pointer context address (may be NULL). */
> +static inline
> +void *hp_ctx_addr(struct hp_ctx ctx)
> +{
> + return ctx.addr;
> +}
