README
1============
2LITMUS TESTS
3============
4
5Each subdirectory contains litmus tests that are typical to describe the
6semantics of respective kernel APIs.
7For more information about how to "run" a litmus test or how to generate
8a kernel test module based on a litmus test, please see
9tools/memory-model/README.
10
11
12atomic (/atomic directory)
13--------------------------
14
15Atomic-RMW+mb__after_atomic-is-stronger-than-acquire.litmus
16 Test that an atomic RMW followed by a smp_mb__after_atomic() is
17 stronger than a normal acquire: both the read and write parts of
18 the RMW are ordered before the subsequential memory accesses.
19
20Atomic-RMW-ops-are-atomic-WRT-atomic_set.litmus
21 Test that atomic_set() cannot break the atomicity of atomic RMWs.
22 NOTE: Require herd7 7.56 or later which supports "(void)expr".
23
24cmpxchg-fail-ordered-1.litmus
25 Demonstrate that a failing cmpxchg() operation acts as a full barrier
26 when followed by smp_mb__after_atomic().
27
28cmpxchg-fail-ordered-2.litmus
29 Demonstrate that a failing cmpxchg() operation acts as an acquire
30 operation when followed by smp_mb__after_atomic().
31
32cmpxchg-fail-unordered-1.litmus
33 Demonstrate that a failing cmpxchg() operation does not act as a
34 full barrier.
35
36cmpxchg-fail-unordered-2.litmus
37 Demonstrate that a failing cmpxchg() operation does not act as an
38 acquire operation.
39
40
41locking (/locking directory)
42----------------------------
43
44DCL-broken.litmus
45 Demonstrates that double-checked locking needs more than just
46 the obvious lock acquisitions and releases.
47
48DCL-fixed.litmus
49 Demonstrates corrected double-checked locking that uses
50 smp_store_release() and smp_load_acquire() in addition to the
51 obvious lock acquisitions and releases.
52
53RM-broken.litmus
54 Demonstrates problems with "roach motel" locking, where code is
55 freely moved into lock-based critical sections. This example also
56 shows how to use the "filter" clause to discard executions that
57 would be excluded by other code not modeled in the litmus test.
58 Note also that this "roach motel" optimization is emulated by
59 physically moving P1()'s two reads from x under the lock.
60
61 What is a roach motel? This is from an old advertisement for
62 a cockroach trap, much later featured in one of the "Men in
63 Black" movies. "The roaches check in. They don't check out."
64
65RM-fixed.litmus
66 The counterpart to RM-broken.litmus, showing P0()'s two loads from
67 x safely outside of the critical section.
68
69
70RCU (/rcu directory)
71--------------------
72
73MP+onceassign+derefonce.litmus (under tools/memory-model/litmus-tests/)
74 Demonstrates the use of rcu_assign_pointer() and rcu_dereference() to
75 ensure that an RCU reader will not see pre-initialization garbage.
76
77RCU+sync+read.litmus
78RCU+sync+free.litmus
79 Both the above litmus tests demonstrate the RCU grace period guarantee
80 that an RCU read-side critical section can never span a grace period.
81