xref: /linux/tools/memory-model/linux-kernel.cat (revision 44f57d78) 
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 | Sync-srcu] ; 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 * Effects of read-side critical sections proceed from the rcu_read_unlock()
95 * or srcu_read_unlock() backwards on the one hand, and from the
96 * rcu_read_lock() or srcu_read_lock() forwards on the other hand.
97 *
98 * In the definition of rcu-fence below, the po term at the left-hand side
99 * of each disjunct and the po? term at the right-hand end have been factored
100 * out.  They have been moved into the definitions of rcu-link and rb.
101 * This was necessary in order to apply the "& loc" tests correctly.
102 *)
103let rcu-gp = [Sync-rcu]		(* Compare with gp *)
104let srcu-gp = [Sync-srcu]
105let rcu-rscsi = rcu-rscs^-1
106let srcu-rscsi = srcu-rscs^-1
107
108(*
109 * The synchronize_rcu() strong fence is special in that it can order not
110 * one but two non-rf relations, but only in conjunction with an RCU
111 * read-side critical section.
112 *)
113let rcu-link = po? ; hb* ; pb* ; prop ; po
114
115(*
116 * Any sequence containing at least as many grace periods as RCU read-side
117 * critical sections (joined by rcu-link) acts as a generalized strong fence.
118 * Likewise for SRCU grace periods and read-side critical sections, provided
119 * the synchronize_srcu() and srcu_read_[un]lock() calls refer to the same
120 * struct srcu_struct location.
121 *)
122let rec rcu-fence = rcu-gp | srcu-gp |
123	(rcu-gp ; rcu-link ; rcu-rscsi) |
124	((srcu-gp ; rcu-link ; srcu-rscsi) & loc) |
125	(rcu-rscsi ; rcu-link ; rcu-gp) |
126	((srcu-rscsi ; rcu-link ; srcu-gp) & loc) |
127	(rcu-gp ; rcu-link ; rcu-fence ; rcu-link ; rcu-rscsi) |
128	((srcu-gp ; rcu-link ; rcu-fence ; rcu-link ; srcu-rscsi) & loc) |
129	(rcu-rscsi ; rcu-link ; rcu-fence ; rcu-link ; rcu-gp) |
130	((srcu-rscsi ; rcu-link ; rcu-fence ; rcu-link ; srcu-gp) & loc) |
131	(rcu-fence ; rcu-link ; rcu-fence)
132
133(* rb orders instructions just as pb does *)
134let rb = prop ; po ; rcu-fence ; po? ; hb* ; pb*
135
136irreflexive rb as rcu
137
138(*
139 * The happens-before, propagation, and rcu constraints are all
140 * expressions of temporal ordering.  They could be replaced by
141 * a single constraint on an "executes-before" relation, xb:
142 *
143 * let xb = hb | pb | rb
144 * acyclic xb as executes-before
145 *)
146