xref: /openbmc/linux/tools/memory-model/linux-kernel.cat (revision 5b735eb1ce481b2f1674a47c0995944b1cb6f5d5)

// SPDX-License-Identifier: GPL-2.0+
(*
 * Copyright (C) 2015 Jade Alglave <j.alglave@ucl.ac.uk>,
 * Copyright (C) 2016 Luc Maranget <luc.maranget@inria.fr> for Inria
 * Copyright (C) 2017 Alan Stern <stern@rowland.harvard.edu>,
 *                    Andrea Parri <parri.andrea@gmail.com>
 *
 * An earlier version of this file appeared in the companion webpage for
 * "Frightening small children and disconcerting grown-ups: Concurrency
 * in the Linux kernel" by Alglave, Maranget, McKenney, Parri, and Stern,
 * which appeared in ASPLOS 2018.
 *)

"Linux-kernel memory consistency model"

(*
 * File "lock.cat" handles locks and is experimental.
 * It can be replaced by include "cos.cat" for tests that do not use locks.
 *)

include "lock.cat"

(*******************)
(* Basic relations *)
(*******************)

(* Fences *)
let rmb = [R \ Noreturn] ; fencerel(Rmb) ; [R \ Noreturn]
let wmb = [W] ; fencerel(Wmb) ; [W]
let mb = ([M] ; fencerel(Mb) ; [M]) |
	([M] ; fencerel(Before-atomic) ; [RMW] ; po? ; [M]) |
	([M] ; po? ; [RMW] ; fencerel(After-atomic) ; [M]) |
	([M] ; po? ; [LKW] ; fencerel(After-spinlock) ; [M]) |
	([M] ; po ; [UL] ; (co | po) ; [LKW] ;
		fencerel(After-unlock-lock) ; [M])
let gp = po ; [Sync-rcu] ; po?

let strong-fence = mb | gp

(* Release Acquire *)
let acq-po = [Acquire] ; po ; [M]
let po-rel = [M] ; po ; [Release]
let po-unlock-rf-lock-po = po ; [UL] ; rf ; [LKR] ; po

(**********************************)
(* Fundamental coherence ordering *)
(**********************************)

(* Sequential Consistency Per Variable *)
let com = rf | co | fr
acyclic po-loc | com as coherence

(* Atomic Read-Modify-Write *)
empty rmw & (fre ; coe) as atomic

(**********************************)
(* Instruction execution ordering *)
(**********************************)

(* Preserved Program Order *)
let dep = addr | data
let rwdep = (dep | ctrl) ; [W]
let overwrite = co | fr
let to-w = rwdep | (overwrite & int)
let to-r = addr | (dep ; rfi)
let fence = strong-fence | wmb | po-rel | rmb | acq-po
let ppo = to-r | to-w | fence | (po-unlock-rf-lock-po & int)

(* Propagation: Ordering from release operations and strong fences. *)
let A-cumul(r) = rfe? ; r
let cumul-fence = A-cumul(strong-fence | po-rel) | wmb | po-unlock-rf-lock-po
let prop = (overwrite & ext)? ; cumul-fence* ; rfe?

(*
 * Happens Before: Ordering from the passage of time.
 * No fences needed here for prop because relation confined to one process.
 *)
let hb = ppo | rfe | ((prop \ id) & int)
acyclic hb as happens-before

(****************************************)
(* Write and fence propagation ordering *)
(****************************************)

(* Propagation: Each non-rf link needs a strong fence. *)
let pb = prop ; strong-fence ; hb*
acyclic pb as propagation

(*******)
(* RCU *)
(*******)

(*
 * Effect of read-side critical section proceeds from the rcu_read_lock()
 * onward on the one hand and from the rcu_read_unlock() backwards on the
 * other hand.
 *)
let rscs = po ; crit^-1 ; po?

(*
 * The synchronize_rcu() strong fence is special in that it can order not
 * one but two non-rf relations, but only in conjunction with an RCU
 * read-side critical section.
 *)
let rcu-link = hb* ; pb* ; prop

(*
 * Any sequence containing at least as many grace periods as RCU read-side
 * critical sections (joined by rcu-link) acts as a generalized strong fence.
 *)
let rec rcu-fence = gp |
	(gp ; rcu-link ; rscs) |
	(rscs ; rcu-link ; gp) |
	(gp ; rcu-link ; rcu-fence ; rcu-link ; rscs) |
	(rscs ; rcu-link ; rcu-fence ; rcu-link ; gp) |
	(rcu-fence ; rcu-link ; rcu-fence)

(* rb orders instructions just as pb does *)
let rb = prop ; rcu-fence ; hb* ; pb*

irreflexive rb as rcu

(*
 * The happens-before, propagation, and rcu constraints are all
 * expressions of temporal ordering.  They could be replaced by
 * a single constraint on an "executes-before" relation, xb:
 *
 * let xb = hb | pb | rb
 * acyclic xb as executes-before
 *)