1// SPDX-License-Identifier: GPL-2.0+
2(*
3 * Copyright (C) 2015 Jade Alglave <j.alglave@ucl.ac.uk>,
4 * Copyright (C) 2016 Luc Maranget <luc.maranget@inria.fr> for Inria
5 * Copyright (C) 2017 Alan Stern <stern@rowland.harvard.edu>,
6 *                    Andrea Parri <parri.andrea@gmail.com>
7 *
8 * An earlier version of this file appeared in the companion webpage for
9 * "Frightening small children and disconcerting grown-ups: Concurrency
10 * in the Linux kernel" by Alglave, Maranget, McKenney, Parri, and Stern,
11 * which appeared in ASPLOS 2018.
12 *)
13
14"Linux-kernel memory consistency model"
15
16(*
17 * File "lock.cat" handles locks and is experimental.
18 * It can be replaced by include "cos.cat" for tests that do not use locks.
19 *)
20
21include "lock.cat"
22
23(*******************)
24(* Basic relations *)
25(*******************)
26
27(* Fences *)
28let rmb = [R \ Noreturn] ; fencerel(Rmb) ; [R \ Noreturn]
29let wmb = [W] ; fencerel(Wmb) ; [W]
30let mb = ([M] ; fencerel(Mb) ; [M]) |
31	([M] ; fencerel(Before-atomic) ; [RMW] ; po? ; [M]) |
32	([M] ; po? ; [RMW] ; fencerel(After-atomic) ; [M]) |
33	([M] ; po? ; [LKW] ; fencerel(After-spinlock) ; [M]) |
34	([M] ; po ; [UL] ; (co | po) ; [LKW] ;
35		fencerel(After-unlock-lock) ; [M])
36let gp = po ; [Sync-rcu] ; po?
37
38let strong-fence = mb | gp
39
40(* Release Acquire *)
41let acq-po = [Acquire] ; po ; [M]
42let po-rel = [M] ; po ; [Release]
43let po-unlock-rf-lock-po = po ; [UL] ; rf ; [LKR] ; po
44
45(**********************************)
46(* Fundamental coherence ordering *)
47(**********************************)
48
49(* Sequential Consistency Per Variable *)
50let com = rf | co | fr
51acyclic po-loc | com as coherence
52
53(* Atomic Read-Modify-Write *)
54empty rmw & (fre ; coe) as atomic
55
56(**********************************)
57(* Instruction execution ordering *)
58(**********************************)
59
60(* Preserved Program Order *)
61let dep = addr | data
62let rwdep = (dep | ctrl) ; [W]
63let overwrite = co | fr
64let to-w = rwdep | (overwrite & int)
65let to-r = addr | (dep ; rfi)
66let fence = strong-fence | wmb | po-rel | rmb | acq-po
67let ppo = to-r | to-w | fence | (po-unlock-rf-lock-po & int)
68
69(* Propagation: Ordering from release operations and strong fences. *)
70let A-cumul(r) = rfe? ; r
71let cumul-fence = A-cumul(strong-fence | po-rel) | wmb | po-unlock-rf-lock-po
72let prop = (overwrite & ext)? ; cumul-fence* ; rfe?
73
74(*
75 * Happens Before: Ordering from the passage of time.
76 * No fences needed here for prop because relation confined to one process.
77 *)
78let hb = ppo | rfe | ((prop \ id) & int)
79acyclic hb as happens-before
80
81(****************************************)
82(* Write and fence propagation ordering *)
83(****************************************)
84
85(* Propagation: Each non-rf link needs a strong fence. *)
86let pb = prop ; strong-fence ; hb*
87acyclic pb as propagation
88
89(*******)
90(* RCU *)
91(*******)
92
93(*
94 * Effect of read-side critical section proceeds from the rcu_read_lock()
95 * onward on the one hand and from the rcu_read_unlock() backwards on the
96 * other hand.
97 *)
98let rscs = po ; crit^-1 ; po?
99
100(*
101 * The synchronize_rcu() strong fence is special in that it can order not
102 * one but two non-rf relations, but only in conjunction with an RCU
103 * read-side critical section.
104 *)
105let rcu-link = hb* ; pb* ; prop
106
107(*
108 * Any sequence containing at least as many grace periods as RCU read-side
109 * critical sections (joined by rcu-link) acts as a generalized strong fence.
110 *)
111let rec rcu-fence = gp |
112	(gp ; rcu-link ; rscs) |
113	(rscs ; rcu-link ; gp) |
114	(gp ; rcu-link ; rcu-fence ; rcu-link ; rscs) |
115	(rscs ; rcu-link ; rcu-fence ; rcu-link ; gp) |
116	(rcu-fence ; rcu-link ; rcu-fence)
117
118(* rb orders instructions just as pb does *)
119let rb = prop ; rcu-fence ; hb* ; pb*
120
121irreflexive rb as rcu
122
123(*
124 * The happens-before, propagation, and rcu constraints are all
125 * expressions of temporal ordering.  They could be replaced by
126 * a single constraint on an "executes-before" relation, xb:
127 *
128 * let xb = hb | pb | rb
129 * acyclic xb as executes-before
130 *)
131