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