1 ============ !! 1 This directory contains the following litmus tests:
2 LITMUS TESTS <<
3 ============ <<
4 2
5 CoRR+poonceonce+Once.litmus 3 CoRR+poonceonce+Once.litmus
6 Test of read-read coherence, that is, 4 Test of read-read coherence, that is, whether or not two
7 successive reads from the same variabl 5 successive reads from the same variable are ordered.
8 6
9 CoRW+poonceonce+Once.litmus 7 CoRW+poonceonce+Once.litmus
10 Test of read-write coherence, that is, 8 Test of read-write coherence, that is, whether or not a read
11 from a given variable followed by a wr 9 from a given variable followed by a write to that same variable
12 are ordered. 10 are ordered.
13 11
14 CoWR+poonceonce+Once.litmus 12 CoWR+poonceonce+Once.litmus
15 Test of write-read coherence, that is, 13 Test of write-read coherence, that is, whether or not a write
16 to a given variable followed by a read 14 to a given variable followed by a read from that same variable
17 are ordered. 15 are ordered.
18 16
19 CoWW+poonceonce.litmus 17 CoWW+poonceonce.litmus
20 Test of write-write coherence, that is 18 Test of write-write coherence, that is, whether or not two
21 successive writes to the same variable 19 successive writes to the same variable are ordered.
22 20
23 IRIW+fencembonceonces+OnceOnce.litmus 21 IRIW+fencembonceonces+OnceOnce.litmus
24 Test of independent reads from indepen 22 Test of independent reads from independent writes with smp_mb()
25 between each pairs of reads. In other 23 between each pairs of reads. In other words, is smp_mb()
26 sufficient to cause two different read 24 sufficient to cause two different reading processes to agree on
27 the order of a pair of writes, where e 25 the order of a pair of writes, where each write is to a different
28 variable by a different process? This 26 variable by a different process? This litmus test is forbidden
29 by LKMM's propagation rule. 27 by LKMM's propagation rule.
30 28
31 IRIW+poonceonces+OnceOnce.litmus 29 IRIW+poonceonces+OnceOnce.litmus
32 Test of independent reads from indepen 30 Test of independent reads from independent writes with nothing
33 between each pairs of reads. In other 31 between each pairs of reads. In other words, is anything at all
34 needed to cause two different reading 32 needed to cause two different reading processes to agree on the
35 order of a pair of writes, where each 33 order of a pair of writes, where each write is to a different
36 variable by a different process? 34 variable by a different process?
37 35
38 ISA2+pooncelock+pooncelock+pombonce.litmus 36 ISA2+pooncelock+pooncelock+pombonce.litmus
39 Tests whether the ordering provided by 37 Tests whether the ordering provided by a lock-protected S
40 litmus test is visible to an external 38 litmus test is visible to an external process whose accesses are
41 separated by smp_mb(). This addition !! 39 separated by smp_mb(). This addition of an external process to
42 S is otherwise known as ISA2. 40 S is otherwise known as ISA2.
43 41
44 ISA2+poonceonces.litmus 42 ISA2+poonceonces.litmus
45 As below, but with store-release repla 43 As below, but with store-release replaced with WRITE_ONCE()
46 and load-acquire replaced with READ_ON 44 and load-acquire replaced with READ_ONCE().
47 45
48 ISA2+pooncerelease+poacquirerelease+poacquireo 46 ISA2+pooncerelease+poacquirerelease+poacquireonce.litmus
49 Can a release-acquire chain order a pr 47 Can a release-acquire chain order a prior store against
50 a later load? 48 a later load?
51 49
52 LB+fencembonceonce+ctrlonceonce.litmus 50 LB+fencembonceonce+ctrlonceonce.litmus
53 Does a control dependency and an smp_m 51 Does a control dependency and an smp_mb() suffice for the
54 load-buffering litmus test, where each 52 load-buffering litmus test, where each process reads from one
55 of two variables then writes to the ot 53 of two variables then writes to the other?
56 54
57 LB+poacquireonce+pooncerelease.litmus 55 LB+poacquireonce+pooncerelease.litmus
58 Does a release-acquire pair suffice fo 56 Does a release-acquire pair suffice for the load-buffering
59 litmus test, where each process reads 57 litmus test, where each process reads from one of two variables then
60 writes to the other? 58 writes to the other?
61 59
62 LB+poonceonces.litmus 60 LB+poonceonces.litmus
63 As above, but with store-release repla 61 As above, but with store-release replaced with WRITE_ONCE()
64 and load-acquire replaced with READ_ON 62 and load-acquire replaced with READ_ONCE().
65 63
66 LB+unlocklockonceonce+poacquireonce.litmus <<
67 Does a unlock+lock pair provides order <<
68 load and a store? <<
69 <<
70 MP+onceassign+derefonce.litmus 64 MP+onceassign+derefonce.litmus
71 As below, but with rcu_assign_pointer( 65 As below, but with rcu_assign_pointer() and an rcu_dereference().
72 66
73 MP+polockmbonce+poacquiresilsil.litmus 67 MP+polockmbonce+poacquiresilsil.litmus
74 Protect the access with a lock and an 68 Protect the access with a lock and an smp_mb__after_spinlock()
75 in one process, and use an acquire loa 69 in one process, and use an acquire load followed by a pair of
76 spin_is_locked() calls in the other pr 70 spin_is_locked() calls in the other process.
77 71
78 MP+polockonce+poacquiresilsil.litmus 72 MP+polockonce+poacquiresilsil.litmus
79 Protect the access with a lock in one 73 Protect the access with a lock in one process, and use an
80 acquire load followed by a pair of spi 74 acquire load followed by a pair of spin_is_locked() calls
81 in the other process. 75 in the other process.
82 76
83 MP+polocks.litmus 77 MP+polocks.litmus
84 As below, but with the second access o 78 As below, but with the second access of the writer process
85 and the first access of reader process 79 and the first access of reader process protected by a lock.
86 80
87 MP+poonceonces.litmus 81 MP+poonceonces.litmus
88 As below, but without the smp_rmb() an 82 As below, but without the smp_rmb() and smp_wmb().
89 83
90 MP+pooncerelease+poacquireonce.litmus 84 MP+pooncerelease+poacquireonce.litmus
91 As below, but with a release-acquire c 85 As below, but with a release-acquire chain.
92 86
93 MP+porevlocks.litmus 87 MP+porevlocks.litmus
94 As below, but with the first access of 88 As below, but with the first access of the writer process
95 and the second access of reader proces 89 and the second access of reader process protected by a lock.
96 90
97 MP+unlocklockonceonce+fencermbonceonce.litmus <<
98 Does a unlock+lock pair provides order <<
99 store and another store? <<
100 <<
101 MP+fencewmbonceonce+fencermbonceonce.litmus 91 MP+fencewmbonceonce+fencermbonceonce.litmus
102 Does a smp_wmb() (between the stores) 92 Does a smp_wmb() (between the stores) and an smp_rmb() (between
103 the loads) suffice for the message-pas 93 the loads) suffice for the message-passing litmus test, where one
104 process writes data and then a flag, a 94 process writes data and then a flag, and the other process reads
105 the flag and then the data. (This is 95 the flag and then the data. (This is similar to the ISA2 tests,
106 but with two processes instead of thre 96 but with two processes instead of three.)
107 97
108 R+fencembonceonces.litmus 98 R+fencembonceonces.litmus
109 This is the fully ordered (via smp_mb( 99 This is the fully ordered (via smp_mb()) version of one of
110 the classic counterintuitive litmus te 100 the classic counterintuitive litmus tests that illustrates the
111 effects of store propagation delays. 101 effects of store propagation delays.
112 102
113 R+poonceonces.litmus 103 R+poonceonces.litmus
114 As above, but without the smp_mb() inv 104 As above, but without the smp_mb() invocations.
115 105
116 SB+fencembonceonces.litmus 106 SB+fencembonceonces.litmus
117 This is the fully ordered (again, via 107 This is the fully ordered (again, via smp_mb() version of store
118 buffering, which forms the core of Dek 108 buffering, which forms the core of Dekker's mutual-exclusion
119 algorithm. 109 algorithm.
120 110
121 SB+poonceonces.litmus 111 SB+poonceonces.litmus
122 As above, but without the smp_mb() inv 112 As above, but without the smp_mb() invocations.
123 113
124 SB+rfionceonce-poonceonces.litmus 114 SB+rfionceonce-poonceonces.litmus
125 This litmus test demonstrates that LKM 115 This litmus test demonstrates that LKMM is not fully multicopy
126 atomic. (Neither is it other multicop 116 atomic. (Neither is it other multicopy atomic.) This litmus test
127 also demonstrates the "locations" debu 117 also demonstrates the "locations" debugging aid, which designates
128 additional registers and locations to 118 additional registers and locations to be printed out in the dump
129 of final states in the herd7 output. 119 of final states in the herd7 output. Without the "locations"
130 statement, only those registers and lo 120 statement, only those registers and locations mentioned in the
131 "exists" clause will be printed. 121 "exists" clause will be printed.
132 122
133 S+poonceonces.litmus 123 S+poonceonces.litmus
134 As below, but without the smp_wmb() an 124 As below, but without the smp_wmb() and acquire load.
135 125
136 S+fencewmbonceonce+poacquireonce.litmus 126 S+fencewmbonceonce+poacquireonce.litmus
137 Can a smp_wmb(), instead of a release, 127 Can a smp_wmb(), instead of a release, and an acquire order
138 a prior store against a subsequent sto 128 a prior store against a subsequent store?
139 129
140 WRC+poonceonces+Once.litmus 130 WRC+poonceonces+Once.litmus
141 WRC+pooncerelease+fencermbonceonce+Once.litmus 131 WRC+pooncerelease+fencermbonceonce+Once.litmus
142 These two are members of an extension 132 These two are members of an extension of the MP litmus-test
143 class in which the first write is move 133 class in which the first write is moved to a separate process.
144 The second is forbidden because smp_st 134 The second is forbidden because smp_store_release() is
145 A-cumulative in LKMM. 135 A-cumulative in LKMM.
146 136
147 Z6.0+pooncelock+pooncelock+pombonce.litmus 137 Z6.0+pooncelock+pooncelock+pombonce.litmus
148 Is the ordering provided by a spin_unl 138 Is the ordering provided by a spin_unlock() and a subsequent
149 spin_lock() sufficient to make orderin 139 spin_lock() sufficient to make ordering apparent to accesses
150 by a process not holding the lock? 140 by a process not holding the lock?
151 141
152 Z6.0+pooncelock+poonceLock+pombonce.litmus 142 Z6.0+pooncelock+poonceLock+pombonce.litmus
153 As above, but with smp_mb__after_spinl 143 As above, but with smp_mb__after_spinlock() immediately
154 following the spin_lock(). 144 following the spin_lock().
155 145
156 Z6.0+pooncerelease+poacquirerelease+fencembonc 146 Z6.0+pooncerelease+poacquirerelease+fencembonceonce.litmus
157 Is the ordering provided by a release- 147 Is the ordering provided by a release-acquire chain sufficient
158 to make ordering apparent to accesses 148 to make ordering apparent to accesses by a process that does
159 not participate in that release-acquir 149 not participate in that release-acquire chain?
160 150
161 A great many more litmus tests are available h 151 A great many more litmus tests are available here:
162 152
163 https://github.com/paulmckrcu/litmus 153 https://github.com/paulmckrcu/litmus
164 <<
165 ================== <<
166 LITMUS TEST NAMING <<
167 ================== <<
168 <<
169 Litmus tests are usually named based on their <<
170 looking at the name tells you what the litmus <<
171 scheme covers litmus tests having a single cyc <<
172 each process exactly once, so litmus tests not <<
173 are named on an ad-hoc basis. <<
174 <<
175 The structure of a litmus-test name is the lit <<
176 sign ("+"), and one string for each process, s <<
177 The end of the name is ".litmus". <<
178 <<
179 The litmus-test classes may be found in the in <<
180 https://www.cl.cam.ac.uk/~pes20/ppc-supplement <<
181 Each class defines the pattern of accesses and <<
182 For example, if the one process writes to a pa <<
183 the other process reads from these same variab <<
184 litmus-test class is "MP" (message passing), w <<
185 left-hand end of the second row of tests on pa <<
186 <<
187 The strings used to identify the actions carri <<
188 complex due to a desire to have short(er) name <<
189 generate these strings from a given litmus tes <<
190 consider the processes from SB+rfionceonce-poo <<
191 <<
192 P0(int *x, int *y) <<
193 { <<
194 int r1; <<
195 int r2; <<
196 <<
197 WRITE_ONCE(*x, 1); <<
198 r1 = READ_ONCE(*x); <<
199 r2 = READ_ONCE(*y); <<
200 } <<
201 <<
202 P1(int *x, int *y) <<
203 { <<
204 int r3; <<
205 int r4; <<
206 <<
207 WRITE_ONCE(*y, 1); <<
208 r3 = READ_ONCE(*y); <<
209 r4 = READ_ONCE(*x); <<
210 } <<
211 <<
212 The next step is to construct a space-separate <<
213 interleaving descriptions of the relation betw <<
214 accesses with descriptions of the second acces <<
215 <<
216 P0()'s WRITE_ONCE() is read by its first READ_ <<
217 reads-from link (rf) and internal to the P0() <<
218 "rfi", which is an abbreviation for "reads-fro <<
219 some of the tools string these abbreviations t <<
220 characters separating processes, the first cha <<
221 resulting in "Rfi". <<
222 <<
223 P0()'s second access is a READ_ONCE(), as oppo <<
224 smp_load_acquire(), so next is "Once". Thus f <<
225 <<
226 P0()'s third access is also a READ_ONCE(), but <<
227 This is related to P0()'s second access by pro <<
228 to a different variable ("d"), and both access <<
229 The resulting descriptor is "PodRR". Because <<
230 READ_ONCE(), we add another "Once" descriptor. <<
231 <<
232 A from-read ("fre") relation links P0()'s thir <<
233 access, and the resulting descriptor is "Fre". <<
234 WRITE_ONCE(), which as before gives the descri <<
235 thus far is thus "Rfi Once PodRR Once Fre Once <<
236 <<
237 The remainder of P1() is similar to P0(), whic <<
238 "Rfi Once PodRR Once". Another fre links P1() <<
239 P0()'s first access, which is WRITE_ONCE(), so <<
240 The full string is thus: <<
241 <<
242 Rfi Once PodRR Once Fre Once Rfi Once <<
243 <<
244 This string can be given to the "norm7" and "c <<
245 produce the name: <<
246 <<
247 $ norm7 -bell linux-kernel.bell \ <<
248 Rfi Once PodRR Once Fre Once R <<
249 sed -e 's/:.*//g' <<
250 SB+rfionceonce-poonceonces <<
251 <<
252 Adding the ".litmus" suffix: SB+rfionceonce-po <<
253 <<
254 The descriptors that describe connections betw <<
255 within the cycle through a given litmus test c <<
256 tool (Rfi, Po, Fre, and so on) or by the linux <<
257 Release, Acquire, and so on). <<
258 <<
259 To see the full list of descriptors, execute t <<
260 <<
261 $ diyone7 -bell linux-kernel.bell -sho <<
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