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(* Release Acquire *)
28let acq-po = [Acquire] ; po ; [M]
29let po-rel = [M] ; po ; [Release]
30let po-unlock-lock-po = po ; [UL] ; (po|rf) ; [LKR] ; po
31
32(* Fences *)
33let R4rmb = R \ Noreturn	(* Reads for which rmb works *)
34let rmb = [R4rmb] ; fencerel(Rmb) ; [R4rmb]
35let wmb = [W] ; fencerel(Wmb) ; [W]
36let mb = ([M] ; fencerel(Mb) ; [M]) |
37	([M] ; fencerel(Before-atomic) ; [RMW] ; po? ; [M]) |
38	([M] ; po? ; [RMW] ; fencerel(After-atomic) ; [M]) |
39	([M] ; po? ; [LKW] ; fencerel(After-spinlock) ; [M]) |
40(*
41 * Note: The po-unlock-lock-po relation only passes the lock to the direct
42 * successor, perhaps giving the impression that the ordering of the
43 * smp_mb__after_unlock_lock() fence only affects a single lock handover.
44 * However, in a longer sequence of lock handovers, the implicit
45 * A-cumulative release fences of lock-release ensure that any stores that
46 * propagate to one of the involved CPUs before it hands over the lock to
47 * the next CPU will also propagate to the final CPU handing over the lock
48 * to the CPU that executes the fence.  Therefore, all those stores are
49 * also affected by the fence.
50 *)
51	([M] ; po-unlock-lock-po ;
52		[After-unlock-lock] ; po ; [M]) |
53	([M] ; po? ; [Srcu-unlock] ; fencerel(After-srcu-read-unlock) ; [M])
54let gp = po ; [Sync-rcu | Sync-srcu] ; po?
55let strong-fence = mb | gp
56
57let nonrw-fence = strong-fence | po-rel | acq-po
58let fence = nonrw-fence | wmb | rmb
59let barrier = fencerel(Barrier | Rmb | Wmb | Mb | Sync-rcu | Sync-srcu |
60		Before-atomic | After-atomic | Acquire | Release |
61		Rcu-lock | Rcu-unlock | Srcu-lock | Srcu-unlock) |
62	(po ; [Release]) | ([Acquire] ; po)
63
64(**********************************)
65(* Fundamental coherence ordering *)
66(**********************************)
67
68(* Sequential Consistency Per Variable *)
69let com = rf | co | fr
70acyclic po-loc | com as coherence
71
72(* Atomic Read-Modify-Write *)
73empty rmw & (fre ; coe) as atomic
74
75(**********************************)
76(* Instruction execution ordering *)
77(**********************************)
78
79(* Preserved Program Order *)
80let dep = addr | data
81let rwdep = (dep | ctrl) ; [W]
82let overwrite = co | fr
83let to-w = rwdep | (overwrite & int) | (addr ; [Plain] ; wmb)
84let to-r = (addr ; [R]) | (dep ; [Marked] ; rfi)
85let ppo = to-r | to-w | (fence & int) | (po-unlock-lock-po & int)
86
87(* Propagation: Ordering from release operations and strong fences. *)
88let A-cumul(r) = (rfe ; [Marked])? ; r
89let rmw-sequence = (rf ; rmw)*
90let cumul-fence = [Marked] ; (A-cumul(strong-fence | po-rel) | wmb |
91	po-unlock-lock-po) ; [Marked] ; rmw-sequence
92let prop = [Marked] ; (overwrite & ext)? ; cumul-fence* ;
93	[Marked] ; rfe? ; [Marked]
94
95(*
96 * Happens Before: Ordering from the passage of time.
97 * No fences needed here for prop because relation confined to one process.
98 *)
99let hb = [Marked] ; (ppo | rfe | ((prop \ id) & int)) ; [Marked]
100acyclic hb as happens-before
101
102(****************************************)
103(* Write and fence propagation ordering *)
104(****************************************)
105
106(* Propagation: Each non-rf link needs a strong fence. *)
107let pb = prop ; strong-fence ; hb* ; [Marked]
108acyclic pb as propagation
109
110(*******)
111(* RCU *)
112(*******)
113
114(*
115 * Effects of read-side critical sections proceed from the rcu_read_unlock()
116 * or srcu_read_unlock() backwards on the one hand, and from the
117 * rcu_read_lock() or srcu_read_lock() forwards on the other hand.
118 *
119 * In the definition of rcu-fence below, the po term at the left-hand side
120 * of each disjunct and the po? term at the right-hand end have been factored
121 * out.  They have been moved into the definitions of rcu-link and rb.
122 * This was necessary in order to apply the "& loc" tests correctly.
123 *)
124let rcu-gp = [Sync-rcu]		(* Compare with gp *)
125let srcu-gp = [Sync-srcu]
126let rcu-rscsi = rcu-rscs^-1
127let srcu-rscsi = srcu-rscs^-1
128
129(*
130 * The synchronize_rcu() strong fence is special in that it can order not
131 * one but two non-rf relations, but only in conjunction with an RCU
132 * read-side critical section.
133 *)
134let rcu-link = po? ; hb* ; pb* ; prop ; po
135
136(*
137 * Any sequence containing at least as many grace periods as RCU read-side
138 * critical sections (joined by rcu-link) induces order like a generalized
139 * inter-CPU strong fence.
140 * Likewise for SRCU grace periods and read-side critical sections, provided
141 * the synchronize_srcu() and srcu_read_[un]lock() calls refer to the same
142 * struct srcu_struct location.
143 *)
144let rec rcu-order = rcu-gp | srcu-gp |
145	(rcu-gp ; rcu-link ; rcu-rscsi) |
146	((srcu-gp ; rcu-link ; srcu-rscsi) & loc) |
147	(rcu-rscsi ; rcu-link ; rcu-gp) |
148	((srcu-rscsi ; rcu-link ; srcu-gp) & loc) |
149	(rcu-gp ; rcu-link ; rcu-order ; rcu-link ; rcu-rscsi) |
150	((srcu-gp ; rcu-link ; rcu-order ; rcu-link ; srcu-rscsi) & loc) |
151	(rcu-rscsi ; rcu-link ; rcu-order ; rcu-link ; rcu-gp) |
152	((srcu-rscsi ; rcu-link ; rcu-order ; rcu-link ; srcu-gp) & loc) |
153	(rcu-order ; rcu-link ; rcu-order)
154let rcu-fence = po ; rcu-order ; po?
155let fence = fence | rcu-fence
156let strong-fence = strong-fence | rcu-fence
157
158(* rb orders instructions just as pb does *)
159let rb = prop ; rcu-fence ; hb* ; pb* ; [Marked]
160
161irreflexive rb as rcu
162
163(*
164 * The happens-before, propagation, and rcu constraints are all
165 * expressions of temporal ordering.  They could be replaced by
166 * a single constraint on an "executes-before" relation, xb:
167 *
168 * let xb = hb | pb | rb
169 * acyclic xb as executes-before
170 *)
171
172(*********************************)
173(* Plain accesses and data races *)
174(*********************************)
175
176(* Warn about plain writes and marked accesses in the same region *)
177let mixed-accesses = ([Plain & W] ; (po-loc \ barrier) ; [Marked]) |
178	([Marked] ; (po-loc \ barrier) ; [Plain & W])
179flag ~empty mixed-accesses as mixed-accesses
180
181(* Executes-before and visibility *)
182let xbstar = (hb | pb | rb)*
183let vis = cumul-fence* ; rfe? ; [Marked] ;
184	((strong-fence ; [Marked] ; xbstar) | (xbstar & int))
185
186(* Boundaries for lifetimes of plain accesses *)
187let w-pre-bounded = [Marked] ; (addr | fence)?
188let r-pre-bounded = [Marked] ; (addr | nonrw-fence |
189	([R4rmb] ; fencerel(Rmb) ; [~Noreturn]))?
190let w-post-bounded = fence? ; [Marked] ; rmw-sequence
191let r-post-bounded = (nonrw-fence | ([~Noreturn] ; fencerel(Rmb) ; [R4rmb]))? ;
192	[Marked]
193
194(* Visibility and executes-before for plain accesses *)
195let ww-vis = fence | (strong-fence ; xbstar ; w-pre-bounded) |
196	(w-post-bounded ; vis ; w-pre-bounded)
197let wr-vis = fence | (strong-fence ; xbstar ; r-pre-bounded) |
198	(w-post-bounded ; vis ; r-pre-bounded)
199let rw-xbstar = fence | (r-post-bounded ; xbstar ; w-pre-bounded)
200
201(* Potential races *)
202let pre-race = ext & ((Plain * M) | ((M \ IW) * Plain))
203
204(* Coherence requirements for plain accesses *)
205let wr-incoh = pre-race & rf & rw-xbstar^-1
206let rw-incoh = pre-race & fr & wr-vis^-1
207let ww-incoh = pre-race & co & ww-vis^-1
208empty (wr-incoh | rw-incoh | ww-incoh) as plain-coherence
209
210(* Actual races *)
211let ww-nonrace = ww-vis & ((Marked * W) | rw-xbstar) & ((W * Marked) | wr-vis)
212let ww-race = (pre-race & co) \ ww-nonrace
213let wr-race = (pre-race & (co? ; rf)) \ wr-vis \ rw-xbstar^-1
214let rw-race = (pre-race & fr) \ rw-xbstar
215
216flag ~empty (ww-race | wr-race | rw-race) as data-race
217