From 7d874db213cdb17f20c4960e314bcce328d2b61c Mon Sep 17 00:00:00 2001 From: Andy Wang Date: Thu, 12 May 2022 22:04:37 +0100 Subject: [PATCH] Add tests showing weak memory behaviours --- .../consistency.rs} | 39 +--------- .../consistency.stderr} | 0 .../weak_memory/imperfectly_overlapping.rs | 29 +++++++ tests/run-pass/weak_memory/weak.rs | 77 +++++++++++++++++++ tests/run-pass/weak_memory/weak.stderr | 2 + 5 files changed, 112 insertions(+), 35 deletions(-) rename tests/run-pass/{concurrency/weak_memory.rs => weak_memory/consistency.rs} (80%) rename tests/run-pass/{concurrency/weak_memory.stderr => weak_memory/consistency.stderr} (100%) create mode 100644 tests/run-pass/weak_memory/imperfectly_overlapping.rs create mode 100644 tests/run-pass/weak_memory/weak.rs create mode 100644 tests/run-pass/weak_memory/weak.stderr diff --git a/tests/run-pass/concurrency/weak_memory.rs b/tests/run-pass/weak_memory/consistency.rs similarity index 80% rename from tests/run-pass/concurrency/weak_memory.rs rename to tests/run-pass/weak_memory/consistency.rs index e85c2d1960c..d7c44f6ac28 100644 --- a/tests/run-pass/concurrency/weak_memory.rs +++ b/tests/run-pass/weak_memory/consistency.rs @@ -1,8 +1,8 @@ // ignore-windows: Concurrency on Windows is not supported yet. // compile-flags: -Zmiri-ignore-leaks -Zmiri-disable-stacked-borrows -// Weak memory emulation tests. All of the following test if -// our weak memory emulation produces any inconsistent execution outcomes +// The following tests check whether our weak memory emulation produces +// any inconsistent execution outcomes // // Due to the random nature of choosing valid stores, it is always // possible that our tests spuriously succeeds: even though our weak @@ -12,15 +12,6 @@ // // To mitigate this, each test is ran enough times such that the chance // of spurious success is very low. These tests never supriously fail. -// -// Note that we can't effectively test whether our weak memory emulation -// can produce *all* consistent execution outcomes. This may be possible -// if Miri's scheduler is sufficiently random and explores all possible -// interleavings of our small test cases after a reasonable number of runs. -// However, since Miri's scheduler is not even pre-emptive, there will -// always be possible interleavings (and possible execution outcomes), -// that can never be observed regardless of how weak memory emulation is -// implemented. // Test cases and their consistent outcomes are from // http://svr-pes20-cppmem.cl.cam.ac.uk/cppmem/ @@ -28,10 +19,9 @@ // M. Batty, S. Owens, S. Sarkar, P. Sewell and T. Weber, // "Mathematizing C++ concurrency", ACM SIGPLAN Notices, vol. 46, no. 1, pp. 55-66, 2011. // Available: https://ss265.host.cs.st-andrews.ac.uk/papers/n3132.pdf. -#![feature(atomic_from_mut)] +use std::sync::atomic::AtomicUsize; use std::sync::atomic::Ordering::*; -use std::sync::atomic::{AtomicU16, AtomicU32, AtomicUsize}; use std::thread::{spawn, yield_now}; #[derive(Copy, Clone)] @@ -41,7 +31,7 @@ unsafe impl Send for EvilSend {} unsafe impl Sync for EvilSend {} // We can't create static items because we need to run each test -// multiple tests +// multiple times fn static_atomic(val: usize) -> &'static AtomicUsize { let ret = Box::leak(Box::new(AtomicUsize::new(val))); // A workaround to put the initialisation value in the store buffer @@ -190,26 +180,6 @@ fn test_mixed_access() { assert_eq!(r2, 2); } -// Strictly speaking, atomic accesses that imperfectly overlap with existing -// atomic objects are UB. Nonetheless we'd like to provide a sane value when -// the access is not racy. -fn test_imperfectly_overlapping_access() { - let mut qword = AtomicU32::new(42); - assert_eq!(qword.load(Relaxed), 42); - qword.store(u32::to_be(0xabbafafa), Relaxed); - - let qword_mut = qword.get_mut(); - - let dwords_mut = unsafe { std::mem::transmute::<&mut u32, &mut [u16; 2]>(qword_mut) }; - - let (hi_mut, lo_mut) = dwords_mut.split_at_mut(1); - - let (hi, lo) = (AtomicU16::from_mut(&mut hi_mut[0]), AtomicU16::from_mut(&mut lo_mut[0])); - - assert_eq!(u16::from_be(hi.load(Relaxed)), 0xabba); - assert_eq!(u16::from_be(lo.load(Relaxed)), 0xfafa); -} - // The following two tests are taken from Repairing Sequential Consistency in C/C++11 // by Lahav et al. // https://plv.mpi-sws.org/scfix/paper.pdf @@ -236,7 +206,6 @@ fn test_sc_store_buffering() { } pub fn main() { - test_imperfectly_overlapping_access(); // TODO: does this make chances of spurious success // "sufficiently low"? This also takes a long time to run, // prehaps each function should be its own test case so they diff --git a/tests/run-pass/concurrency/weak_memory.stderr b/tests/run-pass/weak_memory/consistency.stderr similarity index 100% rename from tests/run-pass/concurrency/weak_memory.stderr rename to tests/run-pass/weak_memory/consistency.stderr diff --git a/tests/run-pass/weak_memory/imperfectly_overlapping.rs b/tests/run-pass/weak_memory/imperfectly_overlapping.rs new file mode 100644 index 00000000000..2a8e8e5f323 --- /dev/null +++ b/tests/run-pass/weak_memory/imperfectly_overlapping.rs @@ -0,0 +1,29 @@ +// ignore-windows: Concurrency on Windows is not supported yet. +#![feature(atomic_from_mut)] + +use std::sync::atomic::Ordering::*; +use std::sync::atomic::{AtomicU16, AtomicU32}; + +// Strictly speaking, atomic accesses that imperfectly overlap with existing +// atomic objects are UB. Nonetheless we'd like to provide a sane value when +// the access is not racy. +fn test_same_thread() { + let mut qword = AtomicU32::new(42); + assert_eq!(qword.load(Relaxed), 42); + qword.store(u32::to_be(0xabbafafa), Relaxed); + + let qword_mut = qword.get_mut(); + + let dwords_mut = unsafe { std::mem::transmute::<&mut u32, &mut [u16; 2]>(qword_mut) }; + + let (hi_mut, lo_mut) = dwords_mut.split_at_mut(1); + + let (hi, lo) = (AtomicU16::from_mut(&mut hi_mut[0]), AtomicU16::from_mut(&mut lo_mut[0])); + + assert_eq!(u16::from_be(hi.load(Relaxed)), 0xabba); + assert_eq!(u16::from_be(lo.load(Relaxed)), 0xfafa); +} + +pub fn main() { + test_same_thread(); +} diff --git a/tests/run-pass/weak_memory/weak.rs b/tests/run-pass/weak_memory/weak.rs new file mode 100644 index 00000000000..ab0c20cc977 --- /dev/null +++ b/tests/run-pass/weak_memory/weak.rs @@ -0,0 +1,77 @@ +// ignore-windows: Concurrency on Windows is not supported yet. +// compile-flags: -Zmiri-ignore-leaks + +// Tests showing weak memory behaviours are exhibited. All tests +// return true when the desired behaviour is seen. +// This is scheduler and pseudo-RNG dependent, so each test is +// run multiple times until one try returns true. +// Spurious failure is possible, if you are really unlucky with +// the RNG. + +use std::sync::atomic::AtomicUsize; +use std::sync::atomic::Ordering::*; +use std::thread::spawn; + +#[derive(Copy, Clone)] +struct EvilSend(pub T); + +unsafe impl Send for EvilSend {} +unsafe impl Sync for EvilSend {} + +// We can't create static items because we need to run each test +// multiple times +fn static_atomic(val: usize) -> &'static AtomicUsize { + let ret = Box::leak(Box::new(AtomicUsize::new(val))); + // A workaround to put the initialisation value in the store buffer + ret.store(val, Relaxed); + ret +} + +fn relaxed() -> bool { + let x = static_atomic(0); + let j1 = spawn(move || { + x.store(1, Relaxed); + x.store(2, Relaxed); + }); + + let j2 = spawn(move || x.load(Relaxed)); + + j1.join().unwrap(); + let r2 = j2.join().unwrap(); + + r2 == 1 +} + +// https://www.doc.ic.ac.uk/~afd/homepages/papers/pdfs/2017/POPL.pdf Figure 8 +fn seq_cst() -> bool { + let x = static_atomic(0); + + let j1 = spawn(move || { + x.store(1, Relaxed); + }); + + let j2 = spawn(move || { + x.store(2, SeqCst); + x.store(3, SeqCst); + }); + + let j3 = spawn(move || x.load(SeqCst)); + + j1.join().unwrap(); + j2.join().unwrap(); + let r3 = j3.join().unwrap(); + + r3 == 1 +} + +// Asserts that the function returns true at least once in 100 runs +macro_rules! assert_once { + ($f:ident) => { + assert!(std::iter::repeat_with(|| $f()).take(100).any(|x| x)); + }; +} + +pub fn main() { + assert_once!(relaxed); + assert_once!(seq_cst); +} diff --git a/tests/run-pass/weak_memory/weak.stderr b/tests/run-pass/weak_memory/weak.stderr new file mode 100644 index 00000000000..03676519d4f --- /dev/null +++ b/tests/run-pass/weak_memory/weak.stderr @@ -0,0 +1,2 @@ +warning: thread support is experimental and incomplete: weak memory effects are not emulated. +