tools/memory-model/lock.cat

// SPDX-License-Identifier: GPL-2.0+
(*
 * Copyright (C) 2016 Luc Maranget <luc.maranget@inria.fr> for Inria
 * Copyright (C) 2017 Alan Stern <stern@rowland.harvard.edu>
 *)

(*
 * Generate coherence orders and handle lock operations
 *
 * Warning: spin_is_locked() crashes herd7 versions strictly before 7.48.
 * spin_is_locked() is functional from herd7 version 7.49.
 *)

include "cross.cat"

(*
 * The lock-related events generated by herd are as follows:
 *
 * LKR		Lock-Read: the read part of a spin_lock() or successful
 *			spin_trylock() read-modify-write event pair
 * LKW		Lock-Write: the write part of a spin_lock() or successful
 *			spin_trylock() RMW event pair
 * UL		Unlock: a spin_unlock() event
 * LF		Lock-Fail: a failed spin_trylock() event
 * RL		Read-Locked: a spin_is_locked() event which returns True
 * RU		Read-Unlocked: a spin_is_locked() event which returns False
 *
 * LKR and LKW events always come paired, like all RMW event sequences.
 *
 * LKR, LF, RL, and RU are read events; LKR has Acquire ordering.
 * LKW and UL are write events; UL has Release ordering.
 * LKW, LF, RL, and RU have no ordering properties.
 *)

(* Backward compatibility *)
let RL = try RL with emptyset
let RU = try RU with emptyset

(* Treat RL as a kind of LF: a read with no ordering properties *)
let LF = LF | RL

(* There should be no ordinary R or W accesses to spinlocks *)
let ALL-LOCKS = LKR | LKW | UL | LF | RU
flag ~empty [M \ IW] ; loc ; [ALL-LOCKS] as mixed-lock-accesses

(* Link Lock-Reads to their RMW-partner Lock-Writes *)
let lk-rmw = ([LKR] ; po-loc ; [LKW]) \ (po ; po)
let rmw = rmw | lk-rmw

(* The litmus test is invalid if an LKR/LKW event is not part of an RMW pair *)
flag ~empty LKW \ range(lk-rmw) as unpaired-LKW
flag ~empty LKR \ domain(lk-rmw) as unpaired-LKR

(*
 * An LKR must always see an unlocked value; spin_lock() calls nested
 * inside a critical section (for the same lock) always deadlock.
 *)
empty ([LKW] ; po-loc ; [LKR]) \ (po-loc ; [UL] ; po-loc) as lock-nest

(* The final value of a spinlock should not be tested *)
flag ~empty [FW] ; loc ; [ALL-LOCKS] as lock-final

(*
 * Put lock operations in their appropriate classes, but leave UL out of W
 * until after the co relation has been generated.
 *)
let R = R | LKR | LF | RU
let W = W | LKW

let Release = Release | UL
let Acquire = Acquire | LKR

(* Match LKW events to their corresponding UL events *)
let critical = ([LKW] ; po-loc ; [UL]) \ (po-loc ; [LKW | UL] ; po-loc)

flag ~empty UL \ range(critical) as unmatched-unlock

(* Allow up to one unmatched LKW per location; more must deadlock *)
let UNMATCHED-LKW = LKW \ domain(critical)
empty ([UNMATCHED-LKW] ; loc ; [UNMATCHED-LKW]) \ id as unmatched-locks

(* rfi for LF events: link each LKW to the LF events in its critical section *)
let rfi-lf = ([LKW] ; po-loc ; [LF]) \ ([LKW] ; po-loc ; [UL] ; po-loc)

(* rfe for LF events *)
let all-possible-rfe-lf =
	(*
	 * Given an LF event r, compute the possible rfe edges for that event
	 * (all those starting from LKW events in other threads),
	 * and then convert that relation to a set of single-edge relations.
	 *)
	let possible-rfe-lf r =
		let pair-to-relation p = p ++ 0
		in map pair-to-relation ((LKW * {r}) & loc & ext)
	(* Do this for each LF event r that isn't in rfi-lf *)
	in map possible-rfe-lf (LF \ range(rfi-lf))

(* Generate all rf relations for LF events *)
with rfe-lf from cross(all-possible-rfe-lf)
let rf-lf = rfe-lf | rfi-lf

(*
 * RU, i.e., spin_is_locked() returning False, is slightly different.
 * We rely on the memory model to rule out cases where spin_is_locked()
 * within one of the lock's critical sections returns False.
 *)

(* rfi for RU events: an RU may read from the last po-previous UL *)
let rfi-ru = ([UL] ; po-loc ; [RU]) \ ([UL] ; po-loc ; [LKW] ; po-loc)

(* rfe for RU events: an RU may read from an external UL or the initial write *)
let all-possible-rfe-ru =
	let possible-rfe-ru r =
		let pair-to-relation p = p ++ 0
		in map pair-to-relation (((UL | IW) * {r}) & loc & ext)
	in map possible-rfe-ru RU

(* Generate all rf relations for RU events *)
with rfe-ru from cross(all-possible-rfe-ru)
let rf-ru = rfe-ru | rfi-ru

(* Final rf relation *)
let rf = rf | rf-lf | rf-ru

(* Generate all co relations, including LKW events but not UL *)
let co0 = co0 | ([IW] ; loc ; [LKW]) |
	(([LKW] ; loc ; [UNMATCHED-LKW]) \ [UNMATCHED-LKW])
include "cos-opt.cat"
let W = W | UL
let M = R | W

(* Merge UL events into co *)
let co = (co | critical | (critical^-1 ; co))+
let coe = co & ext
let coi = co & int

(* Merge LKR events into rf *)
let rf = rf | ([IW | UL] ; singlestep(co) ; lk-rmw^-1)
let rfe = rf & ext
let rfi = rf & int

let fr = rf^-1 ; co
let fre = fr & ext
let fri = fr & int

show co,rf,fr