miri/concurrency/data_race.rs
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//! Implementation of a data-race detector using Lamport Timestamps / Vector-clocks
//! based on the Dynamic Race Detection for C++:
//! <https://www.doc.ic.ac.uk/~afd/homepages/papers/pdfs/2017/POPL.pdf>
//! which does not report false-positives when fences are used, and gives better
//! accuracy in presence of read-modify-write operations.
//!
//! The implementation contains modifications to correctly model the changes to the memory model in C++20
//! regarding the weakening of release sequences: <http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0982r1.html>.
//! Relaxed stores now unconditionally block all currently active release sequences and so per-thread tracking of release
//! sequences is not needed.
//!
//! The implementation also models races with memory allocation and deallocation via treating allocation and
//! deallocation as a type of write internally for detecting data-races.
//!
//! Weak memory orders are explored but not all weak behaviours are exhibited, so it can still miss data-races
//! but should not report false-positives
//!
//! Data-race definition from(<https://en.cppreference.com/w/cpp/language/memory_model#Threads_and_data_races>):
//! a data race occurs between two memory accesses if they are on different threads, at least one operation
//! is non-atomic, at least one operation is a write and neither access happens-before the other. Read the link
//! for full definition.
//!
//! This re-uses vector indexes for threads that are known to be unable to report data-races, this is valid
//! because it only re-uses vector indexes once all currently-active (not-terminated) threads have an internal
//! vector clock that happens-after the join operation of the candidate thread. Threads that have not been joined
//! on are not considered. Since the thread's vector clock will only increase and a data-race implies that
//! there is some index x where `clock[x] > thread_clock`, when this is true `clock[candidate-idx] > thread_clock`
//! can never hold and hence a data-race can never be reported in that vector index again.
//! This means that the thread-index can be safely re-used, starting on the next timestamp for the newly created
//! thread.
//!
//! The timestamps used in the data-race detector assign each sequence of non-atomic operations
//! followed by a single atomic or concurrent operation a single timestamp.
//! Write, Read, Write, ThreadJoin will be represented by a single timestamp value on a thread.
//! This is because extra increment operations between the operations in the sequence are not
//! required for accurate reporting of data-race values.
//!
//! As per the paper a threads timestamp is only incremented after a release operation is performed
//! so some atomic operations that only perform acquires do not increment the timestamp. Due to shared
//! code some atomic operations may increment the timestamp when not necessary but this has no effect
//! on the data-race detection code.
use std::cell::{Cell, Ref, RefCell, RefMut};
use std::fmt::Debug;
use std::mem;
use rustc_abi::{Align, HasDataLayout, Size};
use rustc_ast::Mutability;
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_index::{Idx, IndexVec};
use rustc_middle::mir;
use rustc_middle::ty::Ty;
use rustc_span::Span;
use super::vector_clock::{VClock, VTimestamp, VectorIdx};
use super::weak_memory::EvalContextExt as _;
use crate::diagnostics::RacingOp;
use crate::*;
pub type AllocState = VClockAlloc;
/// Valid atomic read-write orderings, alias of atomic::Ordering (not non-exhaustive).
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
pub enum AtomicRwOrd {
Relaxed,
Acquire,
Release,
AcqRel,
SeqCst,
}
/// Valid atomic read orderings, subset of atomic::Ordering.
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
pub enum AtomicReadOrd {
Relaxed,
Acquire,
SeqCst,
}
/// Valid atomic write orderings, subset of atomic::Ordering.
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
pub enum AtomicWriteOrd {
Relaxed,
Release,
SeqCst,
}
/// Valid atomic fence orderings, subset of atomic::Ordering.
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
pub enum AtomicFenceOrd {
Acquire,
Release,
AcqRel,
SeqCst,
}
/// The current set of vector clocks describing the state
/// of a thread, contains the happens-before clock and
/// additional metadata to model atomic fence operations.
#[derive(Clone, Default, Debug)]
pub(super) struct ThreadClockSet {
/// The increasing clock representing timestamps
/// that happen-before this thread.
pub(super) clock: VClock,
/// The set of timestamps that will happen-before this
/// thread once it performs an acquire fence.
fence_acquire: VClock,
/// The last timestamp of happens-before relations that
/// have been released by this thread by a release fence.
fence_release: VClock,
/// Timestamps of the last SC write performed by each
/// thread, updated when this thread performs an SC fence.
/// This is never acquired into the thread's clock, it
/// just limits which old writes can be seen in weak memory emulation.
pub(super) write_seqcst: VClock,
/// Timestamps of the last SC fence performed by each
/// thread, updated when this thread performs an SC read.
/// This is never acquired into the thread's clock, it
/// just limits which old writes can be seen in weak memory emulation.
pub(super) read_seqcst: VClock,
}
impl ThreadClockSet {
/// Apply the effects of a release fence to this
/// set of thread vector clocks.
#[inline]
fn apply_release_fence(&mut self) {
self.fence_release.clone_from(&self.clock);
}
/// Apply the effects of an acquire fence to this
/// set of thread vector clocks.
#[inline]
fn apply_acquire_fence(&mut self) {
self.clock.join(&self.fence_acquire);
}
/// Increment the happens-before clock at a
/// known index.
#[inline]
fn increment_clock(&mut self, index: VectorIdx, current_span: Span) {
self.clock.increment_index(index, current_span);
}
/// Join the happens-before clock with that of
/// another thread, used to model thread join
/// operations.
fn join_with(&mut self, other: &ThreadClockSet) {
self.clock.join(&other.clock);
}
}
/// Error returned by finding a data race
/// should be elaborated upon.
#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
pub struct DataRace;
/// Externally stored memory cell clocks
/// explicitly to reduce memory usage for the
/// common case where no atomic operations
/// exists on the memory cell.
#[derive(Clone, PartialEq, Eq, Debug)]
struct AtomicMemoryCellClocks {
/// The clock-vector of the timestamp of the last atomic
/// read operation performed by each thread.
/// This detects potential data-races between atomic read
/// and non-atomic write operations.
read_vector: VClock,
/// The clock-vector of the timestamp of the last atomic
/// write operation performed by each thread.
/// This detects potential data-races between atomic write
/// and non-atomic read or write operations.
write_vector: VClock,
/// Synchronization vector for acquire-release semantics
/// contains the vector of timestamps that will
/// happen-before a thread if an acquire-load is
/// performed on the data.
sync_vector: VClock,
/// The size of accesses to this atomic location.
/// We use this to detect non-synchronized mixed-size accesses. Since all accesses must be
/// aligned to their size, this is sufficient to detect imperfectly overlapping accesses.
/// `None` indicates that we saw multiple different sizes, which is okay as long as all accesses are reads.
size: Option<Size>,
}
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
enum AtomicAccessType {
Load(AtomicReadOrd),
Store,
Rmw,
}
/// Type of a non-atomic read operation.
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
pub enum NaReadType {
/// Standard unsynchronized write.
Read,
// An implicit read generated by a retag.
Retag,
}
impl NaReadType {
fn description(self) -> &'static str {
match self {
NaReadType::Read => "non-atomic read",
NaReadType::Retag => "retag read",
}
}
}
/// Type of a non-atomic write operation: allocating memory, non-atomic writes, and
/// deallocating memory are all treated as writes for the purpose of the data-race detector.
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
pub enum NaWriteType {
/// Allocate memory.
Allocate,
/// Standard unsynchronized write.
Write,
// An implicit write generated by a retag.
Retag,
/// Deallocate memory.
/// Note that when memory is deallocated first, later non-atomic accesses
/// will be reported as use-after-free, not as data races.
/// (Same for `Allocate` above.)
Deallocate,
}
impl NaWriteType {
fn description(self) -> &'static str {
match self {
NaWriteType::Allocate => "creating a new allocation",
NaWriteType::Write => "non-atomic write",
NaWriteType::Retag => "retag write",
NaWriteType::Deallocate => "deallocation",
}
}
}
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
enum AccessType {
NaRead(NaReadType),
NaWrite(NaWriteType),
AtomicLoad,
AtomicStore,
AtomicRmw,
}
/// Per-byte vector clock metadata for data-race detection.
#[derive(Clone, PartialEq, Eq, Debug)]
struct MemoryCellClocks {
/// The vector-clock timestamp and the thread that did the last non-atomic write. We don't need
/// a full `VClock` here, it's always a single thread and nothing synchronizes, so the effective
/// clock is all-0 except for the thread that did the write.
write: (VectorIdx, VTimestamp),
/// The type of operation that the write index represents,
/// either newly allocated memory, a non-atomic write or
/// a deallocation of memory.
write_type: NaWriteType,
/// The vector-clock of all non-atomic reads that happened since the last non-atomic write
/// (i.e., we join together the "singleton" clocks corresponding to each read). It is reset to
/// zero on each write operation.
read: VClock,
/// Atomic access, acquire, release sequence tracking clocks.
/// For non-atomic memory this value is set to None.
/// For atomic memory, each byte carries this information.
atomic_ops: Option<Box<AtomicMemoryCellClocks>>,
}
/// Extra metadata associated with a thread.
#[derive(Debug, Clone, Default)]
struct ThreadExtraState {
/// The current vector index in use by the
/// thread currently, this is set to None
/// after the vector index has been re-used
/// and hence the value will never need to be
/// read during data-race reporting.
vector_index: Option<VectorIdx>,
/// Thread termination vector clock, this
/// is set on thread termination and is used
/// for joining on threads since the vector_index
/// may be re-used when the join operation occurs.
termination_vector_clock: Option<VClock>,
}
/// Global data-race detection state, contains the currently
/// executing thread as well as the vector-clocks associated
/// with each of the threads.
// FIXME: it is probably better to have one large RefCell, than to have so many small ones.
#[derive(Debug, Clone)]
pub struct GlobalState {
/// Set to true once the first additional
/// thread has launched, due to the dependency
/// between before and after a thread launch.
/// Any data-races must be recorded after this
/// so concurrent execution can ignore recording
/// any data-races.
multi_threaded: Cell<bool>,
/// A flag to mark we are currently performing
/// a data race free action (such as atomic access)
/// to suppress the race detector
ongoing_action_data_race_free: Cell<bool>,
/// Mapping of a vector index to a known set of thread
/// clocks, this is not directly mapping from a thread id
/// since it may refer to multiple threads.
vector_clocks: RefCell<IndexVec<VectorIdx, ThreadClockSet>>,
/// Mapping of a given vector index to the current thread
/// that the execution is representing, this may change
/// if a vector index is re-assigned to a new thread.
vector_info: RefCell<IndexVec<VectorIdx, ThreadId>>,
/// The mapping of a given thread to associated thread metadata.
thread_info: RefCell<IndexVec<ThreadId, ThreadExtraState>>,
/// Potential vector indices that could be re-used on thread creation
/// values are inserted here on after the thread has terminated and
/// been joined with, and hence may potentially become free
/// for use as the index for a new thread.
/// Elements in this set may still require the vector index to
/// report data-races, and can only be re-used after all
/// active vector-clocks catch up with the threads timestamp.
reuse_candidates: RefCell<FxHashSet<VectorIdx>>,
/// We make SC fences act like RMWs on a global location.
/// To implement that, they all release and acquire into this clock.
last_sc_fence: RefCell<VClock>,
/// The timestamp of last SC write performed by each thread.
/// Threads only update their own index here!
last_sc_write_per_thread: RefCell<VClock>,
/// Track when an outdated (weak memory) load happens.
pub track_outdated_loads: bool,
}
impl VisitProvenance for GlobalState {
fn visit_provenance(&self, _visit: &mut VisitWith<'_>) {
// We don't have any tags.
}
}
impl AccessType {
fn description(self, ty: Option<Ty<'_>>, size: Option<Size>) -> String {
let mut msg = String::new();
if let Some(size) = size {
if size == Size::ZERO {
// In this case there were multiple read accesss with different sizes and then a write.
// We will be reporting *one* of the other reads, but we don't have enough information
// to determine which one had which size.
assert!(self == AccessType::AtomicLoad);
assert!(ty.is_none());
return format!("multiple differently-sized atomic loads, including one load");
}
msg.push_str(&format!("{}-byte {}", size.bytes(), msg))
}
msg.push_str(match self {
AccessType::NaRead(w) => w.description(),
AccessType::NaWrite(w) => w.description(),
AccessType::AtomicLoad => "atomic load",
AccessType::AtomicStore => "atomic store",
AccessType::AtomicRmw => "atomic read-modify-write",
});
if let Some(ty) = ty {
msg.push_str(&format!(" of type `{}`", ty));
}
msg
}
fn is_atomic(self) -> bool {
match self {
AccessType::AtomicLoad | AccessType::AtomicStore | AccessType::AtomicRmw => true,
AccessType::NaRead(_) | AccessType::NaWrite(_) => false,
}
}
fn is_read(self) -> bool {
match self {
AccessType::AtomicLoad | AccessType::NaRead(_) => true,
AccessType::NaWrite(_) | AccessType::AtomicStore | AccessType::AtomicRmw => false,
}
}
fn is_retag(self) -> bool {
matches!(
self,
AccessType::NaRead(NaReadType::Retag) | AccessType::NaWrite(NaWriteType::Retag)
)
}
}
impl AtomicMemoryCellClocks {
fn new(size: Size) -> Self {
AtomicMemoryCellClocks {
read_vector: Default::default(),
write_vector: Default::default(),
sync_vector: Default::default(),
size: Some(size),
}
}
}
impl MemoryCellClocks {
/// Create a new set of clocks representing memory allocated
/// at a given vector timestamp and index.
fn new(alloc: VTimestamp, alloc_index: VectorIdx) -> Self {
MemoryCellClocks {
read: VClock::default(),
write: (alloc_index, alloc),
write_type: NaWriteType::Allocate,
atomic_ops: None,
}
}
#[inline]
fn write_was_before(&self, other: &VClock) -> bool {
// This is the same as `self.write() <= other` but
// without actually manifesting a clock for `self.write`.
self.write.1 <= other[self.write.0]
}
#[inline]
fn write(&self) -> VClock {
VClock::new_with_index(self.write.0, self.write.1)
}
/// Load the internal atomic memory cells if they exist.
#[inline]
fn atomic(&self) -> Option<&AtomicMemoryCellClocks> {
self.atomic_ops.as_deref()
}
/// Load the internal atomic memory cells if they exist.
#[inline]
fn atomic_mut_unwrap(&mut self) -> &mut AtomicMemoryCellClocks {
self.atomic_ops.as_deref_mut().unwrap()
}
/// Load or create the internal atomic memory metadata if it does not exist. Also ensures we do
/// not do mixed-size atomic accesses, and updates the recorded atomic access size.
fn atomic_access(
&mut self,
thread_clocks: &ThreadClockSet,
size: Size,
write: bool,
) -> Result<&mut AtomicMemoryCellClocks, DataRace> {
match self.atomic_ops {
Some(ref mut atomic) => {
// We are good if the size is the same or all atomic accesses are before our current time.
if atomic.size == Some(size) {
Ok(atomic)
} else if atomic.read_vector <= thread_clocks.clock
&& atomic.write_vector <= thread_clocks.clock
{
// We are fully ordered after all previous accesses, so we can change the size.
atomic.size = Some(size);
Ok(atomic)
} else if !write && atomic.write_vector <= thread_clocks.clock {
// This is a read, and it is ordered after the last write. It's okay for the
// sizes to mismatch, as long as no writes with a different size occur later.
atomic.size = None;
Ok(atomic)
} else {
Err(DataRace)
}
}
None => {
self.atomic_ops = Some(Box::new(AtomicMemoryCellClocks::new(size)));
Ok(self.atomic_ops.as_mut().unwrap())
}
}
}
/// Update memory cell data-race tracking for atomic
/// load acquire semantics, is a no-op if this memory was
/// not used previously as atomic memory.
fn load_acquire(
&mut self,
thread_clocks: &mut ThreadClockSet,
index: VectorIdx,
access_size: Size,
) -> Result<(), DataRace> {
self.atomic_read_detect(thread_clocks, index, access_size)?;
if let Some(atomic) = self.atomic() {
thread_clocks.clock.join(&atomic.sync_vector);
}
Ok(())
}
/// Update memory cell data-race tracking for atomic
/// load relaxed semantics, is a no-op if this memory was
/// not used previously as atomic memory.
fn load_relaxed(
&mut self,
thread_clocks: &mut ThreadClockSet,
index: VectorIdx,
access_size: Size,
) -> Result<(), DataRace> {
self.atomic_read_detect(thread_clocks, index, access_size)?;
if let Some(atomic) = self.atomic() {
thread_clocks.fence_acquire.join(&atomic.sync_vector);
}
Ok(())
}
/// Update the memory cell data-race tracking for atomic
/// store release semantics.
fn store_release(
&mut self,
thread_clocks: &ThreadClockSet,
index: VectorIdx,
access_size: Size,
) -> Result<(), DataRace> {
self.atomic_write_detect(thread_clocks, index, access_size)?;
let atomic = self.atomic_mut_unwrap(); // initialized by `atomic_write_detect`
atomic.sync_vector.clone_from(&thread_clocks.clock);
Ok(())
}
/// Update the memory cell data-race tracking for atomic
/// store relaxed semantics.
fn store_relaxed(
&mut self,
thread_clocks: &ThreadClockSet,
index: VectorIdx,
access_size: Size,
) -> Result<(), DataRace> {
self.atomic_write_detect(thread_clocks, index, access_size)?;
// The handling of release sequences was changed in C++20 and so
// the code here is different to the paper since now all relaxed
// stores block release sequences. The exception for same-thread
// relaxed stores has been removed.
let atomic = self.atomic_mut_unwrap();
atomic.sync_vector.clone_from(&thread_clocks.fence_release);
Ok(())
}
/// Update the memory cell data-race tracking for atomic
/// store release semantics for RMW operations.
fn rmw_release(
&mut self,
thread_clocks: &ThreadClockSet,
index: VectorIdx,
access_size: Size,
) -> Result<(), DataRace> {
self.atomic_write_detect(thread_clocks, index, access_size)?;
let atomic = self.atomic_mut_unwrap();
atomic.sync_vector.join(&thread_clocks.clock);
Ok(())
}
/// Update the memory cell data-race tracking for atomic
/// store relaxed semantics for RMW operations.
fn rmw_relaxed(
&mut self,
thread_clocks: &ThreadClockSet,
index: VectorIdx,
access_size: Size,
) -> Result<(), DataRace> {
self.atomic_write_detect(thread_clocks, index, access_size)?;
let atomic = self.atomic_mut_unwrap();
atomic.sync_vector.join(&thread_clocks.fence_release);
Ok(())
}
/// Detect data-races with an atomic read, caused by a non-atomic write that does
/// not happen-before the atomic-read.
fn atomic_read_detect(
&mut self,
thread_clocks: &ThreadClockSet,
index: VectorIdx,
access_size: Size,
) -> Result<(), DataRace> {
trace!("Atomic read with vectors: {:#?} :: {:#?}", self, thread_clocks);
let atomic = self.atomic_access(thread_clocks, access_size, /*write*/ false)?;
atomic.read_vector.set_at_index(&thread_clocks.clock, index);
// Make sure the last non-atomic write was before this access.
if self.write_was_before(&thread_clocks.clock) { Ok(()) } else { Err(DataRace) }
}
/// Detect data-races with an atomic write, either with a non-atomic read or with
/// a non-atomic write.
fn atomic_write_detect(
&mut self,
thread_clocks: &ThreadClockSet,
index: VectorIdx,
access_size: Size,
) -> Result<(), DataRace> {
trace!("Atomic write with vectors: {:#?} :: {:#?}", self, thread_clocks);
let atomic = self.atomic_access(thread_clocks, access_size, /*write*/ true)?;
atomic.write_vector.set_at_index(&thread_clocks.clock, index);
// Make sure the last non-atomic write and all non-atomic reads were before this access.
if self.write_was_before(&thread_clocks.clock) && self.read <= thread_clocks.clock {
Ok(())
} else {
Err(DataRace)
}
}
/// Detect races for non-atomic read operations at the current memory cell
/// returns true if a data-race is detected.
fn read_race_detect(
&mut self,
thread_clocks: &mut ThreadClockSet,
index: VectorIdx,
read_type: NaReadType,
current_span: Span,
) -> Result<(), DataRace> {
trace!("Unsynchronized read with vectors: {:#?} :: {:#?}", self, thread_clocks);
if !current_span.is_dummy() {
thread_clocks.clock.index_mut(index).span = current_span;
}
thread_clocks.clock.index_mut(index).set_read_type(read_type);
if self.write_was_before(&thread_clocks.clock) {
// We must be ordered-after all atomic writes.
let race_free = if let Some(atomic) = self.atomic() {
atomic.write_vector <= thread_clocks.clock
} else {
true
};
self.read.set_at_index(&thread_clocks.clock, index);
if race_free { Ok(()) } else { Err(DataRace) }
} else {
Err(DataRace)
}
}
/// Detect races for non-atomic write operations at the current memory cell
/// returns true if a data-race is detected.
fn write_race_detect(
&mut self,
thread_clocks: &mut ThreadClockSet,
index: VectorIdx,
write_type: NaWriteType,
current_span: Span,
) -> Result<(), DataRace> {
trace!("Unsynchronized write with vectors: {:#?} :: {:#?}", self, thread_clocks);
if !current_span.is_dummy() {
thread_clocks.clock.index_mut(index).span = current_span;
}
if self.write_was_before(&thread_clocks.clock) && self.read <= thread_clocks.clock {
let race_free = if let Some(atomic) = self.atomic() {
atomic.write_vector <= thread_clocks.clock
&& atomic.read_vector <= thread_clocks.clock
} else {
true
};
self.write = (index, thread_clocks.clock[index]);
self.write_type = write_type;
if race_free {
self.read.set_zero_vector();
Ok(())
} else {
Err(DataRace)
}
} else {
Err(DataRace)
}
}
}
/// Evaluation context extensions.
impl<'tcx> EvalContextExt<'tcx> for MiriInterpCx<'tcx> {}
pub trait EvalContextExt<'tcx>: MiriInterpCxExt<'tcx> {
/// Perform an atomic read operation at the memory location.
fn read_scalar_atomic(
&self,
place: &MPlaceTy<'tcx>,
atomic: AtomicReadOrd,
) -> InterpResult<'tcx, Scalar> {
let this = self.eval_context_ref();
this.atomic_access_check(place, AtomicAccessType::Load(atomic))?;
// This will read from the last store in the modification order of this location. In case
// weak memory emulation is enabled, this may not be the store we will pick to actually read from and return.
// This is fine with StackedBorrow and race checks because they don't concern metadata on
// the *value* (including the associated provenance if this is an AtomicPtr) at this location.
// Only metadata on the location itself is used.
let scalar = this.allow_data_races_ref(move |this| this.read_scalar(place))?;
let buffered_scalar = this.buffered_atomic_read(place, atomic, scalar, || {
this.validate_atomic_load(place, atomic)
})?;
interp_ok(buffered_scalar.ok_or_else(|| err_ub!(InvalidUninitBytes(None)))?)
}
/// Perform an atomic write operation at the memory location.
fn write_scalar_atomic(
&mut self,
val: Scalar,
dest: &MPlaceTy<'tcx>,
atomic: AtomicWriteOrd,
) -> InterpResult<'tcx> {
let this = self.eval_context_mut();
this.atomic_access_check(dest, AtomicAccessType::Store)?;
// Read the previous value so we can put it in the store buffer later.
// The program didn't actually do a read, so suppress the memory access hooks.
// This is also a very special exception where we just ignore an error -- if this read
// was UB e.g. because the memory is uninitialized, we don't want to know!
let old_val = this.run_for_validation(|this| this.read_scalar(dest)).discard_err();
this.allow_data_races_mut(move |this| this.write_scalar(val, dest))?;
this.validate_atomic_store(dest, atomic)?;
this.buffered_atomic_write(val, dest, atomic, old_val)
}
/// Perform an atomic RMW operation on a memory location.
fn atomic_rmw_op_immediate(
&mut self,
place: &MPlaceTy<'tcx>,
rhs: &ImmTy<'tcx>,
op: mir::BinOp,
not: bool,
atomic: AtomicRwOrd,
) -> InterpResult<'tcx, ImmTy<'tcx>> {
let this = self.eval_context_mut();
this.atomic_access_check(place, AtomicAccessType::Rmw)?;
let old = this.allow_data_races_mut(|this| this.read_immediate(place))?;
let val = this.binary_op(op, &old, rhs)?;
let val = if not { this.unary_op(mir::UnOp::Not, &val)? } else { val };
this.allow_data_races_mut(|this| this.write_immediate(*val, place))?;
this.validate_atomic_rmw(place, atomic)?;
this.buffered_atomic_rmw(val.to_scalar(), place, atomic, old.to_scalar())?;
interp_ok(old)
}
/// Perform an atomic exchange with a memory place and a new
/// scalar value, the old value is returned.
fn atomic_exchange_scalar(
&mut self,
place: &MPlaceTy<'tcx>,
new: Scalar,
atomic: AtomicRwOrd,
) -> InterpResult<'tcx, Scalar> {
let this = self.eval_context_mut();
this.atomic_access_check(place, AtomicAccessType::Rmw)?;
let old = this.allow_data_races_mut(|this| this.read_scalar(place))?;
this.allow_data_races_mut(|this| this.write_scalar(new, place))?;
this.validate_atomic_rmw(place, atomic)?;
this.buffered_atomic_rmw(new, place, atomic, old)?;
interp_ok(old)
}
/// Perform an conditional atomic exchange with a memory place and a new
/// scalar value, the old value is returned.
fn atomic_min_max_scalar(
&mut self,
place: &MPlaceTy<'tcx>,
rhs: ImmTy<'tcx>,
min: bool,
atomic: AtomicRwOrd,
) -> InterpResult<'tcx, ImmTy<'tcx>> {
let this = self.eval_context_mut();
this.atomic_access_check(place, AtomicAccessType::Rmw)?;
let old = this.allow_data_races_mut(|this| this.read_immediate(place))?;
let lt = this.binary_op(mir::BinOp::Lt, &old, &rhs)?.to_scalar().to_bool()?;
#[rustfmt::skip] // rustfmt makes this unreadable
let new_val = if min {
if lt { &old } else { &rhs }
} else {
if lt { &rhs } else { &old }
};
this.allow_data_races_mut(|this| this.write_immediate(**new_val, place))?;
this.validate_atomic_rmw(place, atomic)?;
this.buffered_atomic_rmw(new_val.to_scalar(), place, atomic, old.to_scalar())?;
// Return the old value.
interp_ok(old)
}
/// Perform an atomic compare and exchange at a given memory location.
/// On success an atomic RMW operation is performed and on failure
/// only an atomic read occurs. If `can_fail_spuriously` is true,
/// then we treat it as a "compare_exchange_weak" operation, and
/// some portion of the time fail even when the values are actually
/// identical.
fn atomic_compare_exchange_scalar(
&mut self,
place: &MPlaceTy<'tcx>,
expect_old: &ImmTy<'tcx>,
new: Scalar,
success: AtomicRwOrd,
fail: AtomicReadOrd,
can_fail_spuriously: bool,
) -> InterpResult<'tcx, Immediate<Provenance>> {
use rand::Rng as _;
let this = self.eval_context_mut();
this.atomic_access_check(place, AtomicAccessType::Rmw)?;
// Failure ordering cannot be stronger than success ordering, therefore first attempt
// to read with the failure ordering and if successful then try again with the success
// read ordering and write in the success case.
// Read as immediate for the sake of `binary_op()`
let old = this.allow_data_races_mut(|this| this.read_immediate(place))?;
// `binary_op` will bail if either of them is not a scalar.
let eq = this.binary_op(mir::BinOp::Eq, &old, expect_old)?;
// If the operation would succeed, but is "weak", fail some portion
// of the time, based on `success_rate`.
let success_rate = 1.0 - this.machine.cmpxchg_weak_failure_rate;
let cmpxchg_success = eq.to_scalar().to_bool()?
&& if can_fail_spuriously {
this.machine.rng.get_mut().gen_bool(success_rate)
} else {
true
};
let res = Immediate::ScalarPair(old.to_scalar(), Scalar::from_bool(cmpxchg_success));
// Update ptr depending on comparison.
// if successful, perform a full rw-atomic validation
// otherwise treat this as an atomic load with the fail ordering.
if cmpxchg_success {
this.allow_data_races_mut(|this| this.write_scalar(new, place))?;
this.validate_atomic_rmw(place, success)?;
this.buffered_atomic_rmw(new, place, success, old.to_scalar())?;
} else {
this.validate_atomic_load(place, fail)?;
// A failed compare exchange is equivalent to a load, reading from the latest store
// in the modification order.
// Since `old` is only a value and not the store element, we need to separately
// find it in our store buffer and perform load_impl on it.
this.perform_read_on_buffered_latest(place, fail)?;
}
// Return the old value.
interp_ok(res)
}
/// Update the data-race detector for an atomic fence on the current thread.
fn atomic_fence(&mut self, atomic: AtomicFenceOrd) -> InterpResult<'tcx> {
let this = self.eval_context_mut();
let current_span = this.machine.current_span();
if let Some(data_race) = &mut this.machine.data_race {
data_race.maybe_perform_sync_operation(
&this.machine.threads,
current_span,
|index, mut clocks| {
trace!("Atomic fence on {:?} with ordering {:?}", index, atomic);
// Apply data-race detection for the current fences
// this treats AcqRel and SeqCst as the same as an acquire
// and release fence applied in the same timestamp.
if atomic != AtomicFenceOrd::Release {
// Either Acquire | AcqRel | SeqCst
clocks.apply_acquire_fence();
}
if atomic == AtomicFenceOrd::SeqCst {
// Behave like an RMW on the global fence location. This takes full care of
// all the SC fence requirements, including C++17 §32.4 [atomics.order]
// paragraph 6 (which would limit what future reads can see). It also rules
// out many legal behaviors, but we don't currently have a model that would
// be more precise.
// Also see the second bullet on page 10 of
// <https://www.cs.tau.ac.il/~orilahav/papers/popl21_robustness.pdf>.
let mut sc_fence_clock = data_race.last_sc_fence.borrow_mut();
sc_fence_clock.join(&clocks.clock);
clocks.clock.join(&sc_fence_clock);
// Also establish some sort of order with the last SC write that happened, globally
// (but this is only respected by future reads).
clocks.write_seqcst.join(&data_race.last_sc_write_per_thread.borrow());
}
// The release fence is last, since both of the above could alter our clock,
// which should be part of what is being released.
if atomic != AtomicFenceOrd::Acquire {
// Either Release | AcqRel | SeqCst
clocks.apply_release_fence();
}
// Increment timestamp in case of release semantics.
interp_ok(atomic != AtomicFenceOrd::Acquire)
},
)
} else {
interp_ok(())
}
}
/// After all threads are done running, this allows data races to occur for subsequent
/// 'administrative' machine accesses (that logically happen outside of the Abstract Machine).
fn allow_data_races_all_threads_done(&mut self) {
let this = self.eval_context_ref();
assert!(this.have_all_terminated());
if let Some(data_race) = &this.machine.data_race {
let old = data_race.ongoing_action_data_race_free.replace(true);
assert!(!old, "cannot nest allow_data_races");
}
}
/// Calls the callback with the "release" clock of the current thread.
/// Other threads can acquire this clock in the future to establish synchronization
/// with this program point.
///
/// The closure will only be invoked if data race handling is on.
fn release_clock<R>(&self, callback: impl FnOnce(&VClock) -> R) -> Option<R> {
let this = self.eval_context_ref();
Some(this.machine.data_race.as_ref()?.release_clock(&this.machine.threads, callback))
}
/// Acquire the given clock into the current thread, establishing synchronization with
/// the moment when that clock snapshot was taken via `release_clock`.
fn acquire_clock(&self, clock: &VClock) {
let this = self.eval_context_ref();
if let Some(data_race) = &this.machine.data_race {
data_race.acquire_clock(clock, &this.machine.threads);
}
}
}
/// Vector clock metadata for a logical memory allocation.
#[derive(Debug, Clone)]
pub struct VClockAlloc {
/// Assigning each byte a MemoryCellClocks.
alloc_ranges: RefCell<RangeMap<MemoryCellClocks>>,
}
impl VisitProvenance for VClockAlloc {
fn visit_provenance(&self, _visit: &mut VisitWith<'_>) {
// No tags or allocIds here.
}
}
impl VClockAlloc {
/// Create a new data-race detector for newly allocated memory.
pub fn new_allocation(
global: &GlobalState,
thread_mgr: &ThreadManager<'_>,
len: Size,
kind: MemoryKind,
current_span: Span,
) -> VClockAlloc {
// Determine the thread that did the allocation, and when it did it.
let (alloc_timestamp, alloc_index) = match kind {
// User allocated and stack memory should track allocation.
MemoryKind::Machine(
MiriMemoryKind::Rust
| MiriMemoryKind::Miri
| MiriMemoryKind::C
| MiriMemoryKind::WinHeap
| MiriMemoryKind::WinLocal
| MiriMemoryKind::Mmap,
)
| MemoryKind::Stack => {
let (alloc_index, clocks) = global.active_thread_state(thread_mgr);
let mut alloc_timestamp = clocks.clock[alloc_index];
alloc_timestamp.span = current_span;
(alloc_timestamp, alloc_index)
}
// Other global memory should trace races but be allocated at the 0 timestamp
// (conceptually they are allocated on the main thread before everything).
MemoryKind::Machine(
MiriMemoryKind::Global
| MiriMemoryKind::Machine
| MiriMemoryKind::Runtime
| MiriMemoryKind::ExternStatic
| MiriMemoryKind::Tls,
)
| MemoryKind::CallerLocation =>
(VTimestamp::ZERO, global.thread_index(ThreadId::MAIN_THREAD)),
};
VClockAlloc {
alloc_ranges: RefCell::new(RangeMap::new(
len,
MemoryCellClocks::new(alloc_timestamp, alloc_index),
)),
}
}
// Find an index, if one exists where the value
// in `l` is greater than the value in `r`.
fn find_gt_index(l: &VClock, r: &VClock) -> Option<VectorIdx> {
trace!("Find index where not {:?} <= {:?}", l, r);
let l_slice = l.as_slice();
let r_slice = r.as_slice();
l_slice
.iter()
.zip(r_slice.iter())
.enumerate()
.find_map(|(idx, (&l, &r))| if l > r { Some(idx) } else { None })
.or_else(|| {
if l_slice.len() > r_slice.len() {
// By invariant, if l_slice is longer
// then one element must be larger.
// This just validates that this is true
// and reports earlier elements first.
let l_remainder_slice = &l_slice[r_slice.len()..];
let idx = l_remainder_slice
.iter()
.enumerate()
.find_map(|(idx, &r)| if r == VTimestamp::ZERO { None } else { Some(idx) })
.expect("Invalid VClock Invariant");
Some(idx + r_slice.len())
} else {
None
}
})
.map(VectorIdx::new)
}
/// Report a data-race found in the program.
/// This finds the two racing threads and the type
/// of data-race that occurred. This will also
/// return info about the memory location the data-race
/// occurred in. The `ty` parameter is used for diagnostics, letting
/// the user know which type was involved in the access.
#[cold]
#[inline(never)]
fn report_data_race<'tcx>(
global: &GlobalState,
thread_mgr: &ThreadManager<'_>,
mem_clocks: &MemoryCellClocks,
access: AccessType,
access_size: Size,
ptr_dbg: interpret::Pointer<AllocId>,
ty: Option<Ty<'_>>,
) -> InterpResult<'tcx> {
let (active_index, active_clocks) = global.active_thread_state(thread_mgr);
let mut other_size = None; // if `Some`, this was a size-mismatch race
let write_clock;
let (other_access, other_thread, other_clock) =
// First check the atomic-nonatomic cases.
if !access.is_atomic() &&
let Some(atomic) = mem_clocks.atomic() &&
let Some(idx) = Self::find_gt_index(&atomic.write_vector, &active_clocks.clock)
{
(AccessType::AtomicStore, idx, &atomic.write_vector)
} else if !access.is_atomic() &&
let Some(atomic) = mem_clocks.atomic() &&
let Some(idx) = Self::find_gt_index(&atomic.read_vector, &active_clocks.clock)
{
(AccessType::AtomicLoad, idx, &atomic.read_vector)
// Then check races with non-atomic writes/reads.
} else if mem_clocks.write.1 > active_clocks.clock[mem_clocks.write.0] {
write_clock = mem_clocks.write();
(AccessType::NaWrite(mem_clocks.write_type), mem_clocks.write.0, &write_clock)
} else if let Some(idx) = Self::find_gt_index(&mem_clocks.read, &active_clocks.clock) {
(AccessType::NaRead(mem_clocks.read[idx].read_type()), idx, &mem_clocks.read)
// Finally, mixed-size races.
} else if access.is_atomic() && let Some(atomic) = mem_clocks.atomic() && atomic.size != Some(access_size) {
// This is only a race if we are not synchronized with all atomic accesses, so find
// the one we are not synchronized with.
other_size = Some(atomic.size.unwrap_or(Size::ZERO));
if let Some(idx) = Self::find_gt_index(&atomic.write_vector, &active_clocks.clock)
{
(AccessType::AtomicStore, idx, &atomic.write_vector)
} else if let Some(idx) =
Self::find_gt_index(&atomic.read_vector, &active_clocks.clock)
{
(AccessType::AtomicLoad, idx, &atomic.read_vector)
} else {
unreachable!(
"Failed to report data-race for mixed-size access: no race found"
)
}
} else {
unreachable!("Failed to report data-race")
};
// Load elaborated thread information about the racing thread actions.
let active_thread_info = global.print_thread_metadata(thread_mgr, active_index);
let other_thread_info = global.print_thread_metadata(thread_mgr, other_thread);
let involves_non_atomic = !access.is_atomic() || !other_access.is_atomic();
// Throw the data-race detection.
let extra = if other_size.is_some() {
assert!(!involves_non_atomic);
Some("overlapping unsynchronized atomic accesses must use the same access size")
} else if access.is_read() && other_access.is_read() {
panic!("there should be no same-size read-read races")
} else {
None
};
Err(err_machine_stop!(TerminationInfo::DataRace {
involves_non_atomic,
extra,
retag_explain: access.is_retag() || other_access.is_retag(),
ptr: ptr_dbg,
op1: RacingOp {
action: other_access.description(None, other_size),
thread_info: other_thread_info,
span: other_clock.as_slice()[other_thread.index()].span_data(),
},
op2: RacingOp {
action: access.description(ty, other_size.map(|_| access_size)),
thread_info: active_thread_info,
span: active_clocks.clock.as_slice()[active_index.index()].span_data(),
},
}))?
}
/// Detect data-races for an unsynchronized read operation. It will not perform
/// data-race detection if `race_detecting()` is false, either due to no threads
/// being created or if it is temporarily disabled during a racy read or write
/// operation for which data-race detection is handled separately, for example
/// atomic read operations. The `ty` parameter is used for diagnostics, letting
/// the user know which type was read.
pub fn read<'tcx>(
&self,
alloc_id: AllocId,
access_range: AllocRange,
read_type: NaReadType,
ty: Option<Ty<'_>>,
machine: &MiriMachine<'_>,
) -> InterpResult<'tcx> {
let current_span = machine.current_span();
let global = machine.data_race.as_ref().unwrap();
if !global.race_detecting() {
return interp_ok(());
}
let (index, mut thread_clocks) = global.active_thread_state_mut(&machine.threads);
let mut alloc_ranges = self.alloc_ranges.borrow_mut();
for (mem_clocks_range, mem_clocks) in
alloc_ranges.iter_mut(access_range.start, access_range.size)
{
if let Err(DataRace) =
mem_clocks.read_race_detect(&mut thread_clocks, index, read_type, current_span)
{
drop(thread_clocks);
// Report data-race.
return Self::report_data_race(
global,
&machine.threads,
mem_clocks,
AccessType::NaRead(read_type),
access_range.size,
interpret::Pointer::new(alloc_id, Size::from_bytes(mem_clocks_range.start)),
ty,
);
}
}
interp_ok(())
}
/// Detect data-races for an unsynchronized write operation. It will not perform
/// data-race detection if `race_detecting()` is false, either due to no threads
/// being created or if it is temporarily disabled during a racy read or write
/// operation. The `ty` parameter is used for diagnostics, letting
/// the user know which type was written.
pub fn write<'tcx>(
&mut self,
alloc_id: AllocId,
access_range: AllocRange,
write_type: NaWriteType,
ty: Option<Ty<'_>>,
machine: &mut MiriMachine<'_>,
) -> InterpResult<'tcx> {
let current_span = machine.current_span();
let global = machine.data_race.as_mut().unwrap();
if !global.race_detecting() {
return interp_ok(());
}
let (index, mut thread_clocks) = global.active_thread_state_mut(&machine.threads);
for (mem_clocks_range, mem_clocks) in
self.alloc_ranges.get_mut().iter_mut(access_range.start, access_range.size)
{
if let Err(DataRace) =
mem_clocks.write_race_detect(&mut thread_clocks, index, write_type, current_span)
{
drop(thread_clocks);
// Report data-race
return Self::report_data_race(
global,
&machine.threads,
mem_clocks,
AccessType::NaWrite(write_type),
access_range.size,
interpret::Pointer::new(alloc_id, Size::from_bytes(mem_clocks_range.start)),
ty,
);
}
}
interp_ok(())
}
}
/// Vector clock state for a stack frame (tracking the local variables
/// that do not have an allocation yet).
#[derive(Debug, Default)]
pub struct FrameState {
local_clocks: RefCell<FxHashMap<mir::Local, LocalClocks>>,
}
/// Stripped-down version of [`MemoryCellClocks`] for the clocks we need to keep track
/// of in a local that does not yet have addressable memory -- and hence can only
/// be accessed from the thread its stack frame belongs to, and cannot be access atomically.
#[derive(Debug)]
struct LocalClocks {
write: VTimestamp,
write_type: NaWriteType,
read: VTimestamp,
}
impl Default for LocalClocks {
fn default() -> Self {
Self { write: VTimestamp::ZERO, write_type: NaWriteType::Allocate, read: VTimestamp::ZERO }
}
}
impl FrameState {
pub fn local_write(&self, local: mir::Local, storage_live: bool, machine: &MiriMachine<'_>) {
let current_span = machine.current_span();
let global = machine.data_race.as_ref().unwrap();
if !global.race_detecting() {
return;
}
let (index, mut thread_clocks) = global.active_thread_state_mut(&machine.threads);
// This should do the same things as `MemoryCellClocks::write_race_detect`.
if !current_span.is_dummy() {
thread_clocks.clock.index_mut(index).span = current_span;
}
let mut clocks = self.local_clocks.borrow_mut();
if storage_live {
let new_clocks = LocalClocks {
write: thread_clocks.clock[index],
write_type: NaWriteType::Allocate,
read: VTimestamp::ZERO,
};
// There might already be an entry in the map for this, if the local was previously
// live already.
clocks.insert(local, new_clocks);
} else {
// This can fail to exist if `race_detecting` was false when the allocation
// occurred, in which case we can backdate this to the beginning of time.
let clocks = clocks.entry(local).or_default();
clocks.write = thread_clocks.clock[index];
clocks.write_type = NaWriteType::Write;
}
}
pub fn local_read(&self, local: mir::Local, machine: &MiriMachine<'_>) {
let current_span = machine.current_span();
let global = machine.data_race.as_ref().unwrap();
if !global.race_detecting() {
return;
}
let (index, mut thread_clocks) = global.active_thread_state_mut(&machine.threads);
// This should do the same things as `MemoryCellClocks::read_race_detect`.
if !current_span.is_dummy() {
thread_clocks.clock.index_mut(index).span = current_span;
}
thread_clocks.clock.index_mut(index).set_read_type(NaReadType::Read);
// This can fail to exist if `race_detecting` was false when the allocation
// occurred, in which case we can backdate this to the beginning of time.
let mut clocks = self.local_clocks.borrow_mut();
let clocks = clocks.entry(local).or_default();
clocks.read = thread_clocks.clock[index];
}
pub fn local_moved_to_memory(
&self,
local: mir::Local,
alloc: &mut VClockAlloc,
machine: &MiriMachine<'_>,
) {
let global = machine.data_race.as_ref().unwrap();
if !global.race_detecting() {
return;
}
let (index, _thread_clocks) = global.active_thread_state_mut(&machine.threads);
// Get the time the last write actually happened. This can fail to exist if
// `race_detecting` was false when the write occurred, in that case we can backdate this
// to the beginning of time.
let local_clocks = self.local_clocks.borrow_mut().remove(&local).unwrap_or_default();
for (_mem_clocks_range, mem_clocks) in alloc.alloc_ranges.get_mut().iter_mut_all() {
// The initialization write for this already happened, just at the wrong timestamp.
// Check that the thread index matches what we expect.
assert_eq!(mem_clocks.write.0, index);
// Convert the local's clocks into memory clocks.
mem_clocks.write = (index, local_clocks.write);
mem_clocks.write_type = local_clocks.write_type;
mem_clocks.read = VClock::new_with_index(index, local_clocks.read);
}
}
}
impl<'tcx> EvalContextPrivExt<'tcx> for MiriInterpCx<'tcx> {}
trait EvalContextPrivExt<'tcx>: MiriInterpCxExt<'tcx> {
/// Temporarily allow data-races to occur. This should only be used in
/// one of these cases:
/// - One of the appropriate `validate_atomic` functions will be called to
/// treat a memory access as atomic.
/// - The memory being accessed should be treated as internal state, that
/// cannot be accessed by the interpreted program.
/// - Execution of the interpreted program execution has halted.
#[inline]
fn allow_data_races_ref<R>(&self, op: impl FnOnce(&MiriInterpCx<'tcx>) -> R) -> R {
let this = self.eval_context_ref();
if let Some(data_race) = &this.machine.data_race {
let old = data_race.ongoing_action_data_race_free.replace(true);
assert!(!old, "cannot nest allow_data_races");
}
let result = op(this);
if let Some(data_race) = &this.machine.data_race {
data_race.ongoing_action_data_race_free.set(false);
}
result
}
/// Same as `allow_data_races_ref`, this temporarily disables any data-race detection and
/// so should only be used for atomic operations or internal state that the program cannot
/// access.
#[inline]
fn allow_data_races_mut<R>(&mut self, op: impl FnOnce(&mut MiriInterpCx<'tcx>) -> R) -> R {
let this = self.eval_context_mut();
if let Some(data_race) = &this.machine.data_race {
let old = data_race.ongoing_action_data_race_free.replace(true);
assert!(!old, "cannot nest allow_data_races");
}
let result = op(this);
if let Some(data_race) = &this.machine.data_race {
data_race.ongoing_action_data_race_free.set(false);
}
result
}
/// Checks that an atomic access is legal at the given place.
fn atomic_access_check(
&self,
place: &MPlaceTy<'tcx>,
access_type: AtomicAccessType,
) -> InterpResult<'tcx> {
let this = self.eval_context_ref();
// Check alignment requirements. Atomics must always be aligned to their size,
// even if the type they wrap would be less aligned (e.g. AtomicU64 on 32bit must
// be 8-aligned).
let align = Align::from_bytes(place.layout.size.bytes()).unwrap();
this.check_ptr_align(place.ptr(), align)?;
// Ensure the allocation is mutable. Even failing (read-only) compare_exchange need mutable
// memory on many targets (i.e., they segfault if taht memory is mapped read-only), and
// atomic loads can be implemented via compare_exchange on some targets. There could
// possibly be some very specific exceptions to this, see
// <https://github.com/rust-lang/miri/pull/2464#discussion_r939636130> for details.
// We avoid `get_ptr_alloc` since we do *not* want to run the access hooks -- the actual
// access will happen later.
let (alloc_id, _offset, _prov) = this
.ptr_try_get_alloc_id(place.ptr(), 0)
.expect("there are no zero-sized atomic accesses");
if this.get_alloc_mutability(alloc_id)? == Mutability::Not {
// See if this is fine.
match access_type {
AtomicAccessType::Rmw | AtomicAccessType::Store => {
throw_ub_format!(
"atomic store and read-modify-write operations cannot be performed on read-only memory\n\
see <https://doc.rust-lang.org/nightly/std/sync/atomic/index.html#atomic-accesses-to-read-only-memory> for more information"
);
}
AtomicAccessType::Load(_)
if place.layout.size > this.tcx.data_layout().pointer_size() =>
{
throw_ub_format!(
"large atomic load operations cannot be performed on read-only memory\n\
these operations often have to be implemented using read-modify-write operations, which require writeable memory\n\
see <https://doc.rust-lang.org/nightly/std/sync/atomic/index.html#atomic-accesses-to-read-only-memory> for more information"
);
}
AtomicAccessType::Load(o) if o != AtomicReadOrd::Relaxed => {
throw_ub_format!(
"non-relaxed atomic load operations cannot be performed on read-only memory\n\
these operations sometimes have to be implemented using read-modify-write operations, which require writeable memory\n\
see <https://doc.rust-lang.org/nightly/std/sync/atomic/index.html#atomic-accesses-to-read-only-memory> for more information"
);
}
_ => {
// Large relaxed loads are fine!
}
}
}
interp_ok(())
}
/// Update the data-race detector for an atomic read occurring at the
/// associated memory-place and on the current thread.
fn validate_atomic_load(
&self,
place: &MPlaceTy<'tcx>,
atomic: AtomicReadOrd,
) -> InterpResult<'tcx> {
let this = self.eval_context_ref();
this.validate_atomic_op(
place,
atomic,
AccessType::AtomicLoad,
move |memory, clocks, index, atomic| {
if atomic == AtomicReadOrd::Relaxed {
memory.load_relaxed(&mut *clocks, index, place.layout.size)
} else {
memory.load_acquire(&mut *clocks, index, place.layout.size)
}
},
)
}
/// Update the data-race detector for an atomic write occurring at the
/// associated memory-place and on the current thread.
fn validate_atomic_store(
&mut self,
place: &MPlaceTy<'tcx>,
atomic: AtomicWriteOrd,
) -> InterpResult<'tcx> {
let this = self.eval_context_mut();
this.validate_atomic_op(
place,
atomic,
AccessType::AtomicStore,
move |memory, clocks, index, atomic| {
if atomic == AtomicWriteOrd::Relaxed {
memory.store_relaxed(clocks, index, place.layout.size)
} else {
memory.store_release(clocks, index, place.layout.size)
}
},
)
}
/// Update the data-race detector for an atomic read-modify-write occurring
/// at the associated memory place and on the current thread.
fn validate_atomic_rmw(
&mut self,
place: &MPlaceTy<'tcx>,
atomic: AtomicRwOrd,
) -> InterpResult<'tcx> {
use AtomicRwOrd::*;
let acquire = matches!(atomic, Acquire | AcqRel | SeqCst);
let release = matches!(atomic, Release | AcqRel | SeqCst);
let this = self.eval_context_mut();
this.validate_atomic_op(
place,
atomic,
AccessType::AtomicRmw,
move |memory, clocks, index, _| {
if acquire {
memory.load_acquire(clocks, index, place.layout.size)?;
} else {
memory.load_relaxed(clocks, index, place.layout.size)?;
}
if release {
memory.rmw_release(clocks, index, place.layout.size)
} else {
memory.rmw_relaxed(clocks, index, place.layout.size)
}
},
)
}
/// Generic atomic operation implementation
fn validate_atomic_op<A: Debug + Copy>(
&self,
place: &MPlaceTy<'tcx>,
atomic: A,
access: AccessType,
mut op: impl FnMut(
&mut MemoryCellClocks,
&mut ThreadClockSet,
VectorIdx,
A,
) -> Result<(), DataRace>,
) -> InterpResult<'tcx> {
let this = self.eval_context_ref();
assert!(access.is_atomic());
let Some(data_race) = &this.machine.data_race else { return interp_ok(()) };
if !data_race.race_detecting() {
return interp_ok(());
}
let size = place.layout.size;
let (alloc_id, base_offset, _prov) = this.ptr_get_alloc_id(place.ptr(), 0)?;
// Load and log the atomic operation.
// Note that atomic loads are possible even from read-only allocations, so `get_alloc_extra_mut` is not an option.
let alloc_meta = this.get_alloc_extra(alloc_id)?.data_race.as_ref().unwrap();
trace!(
"Atomic op({}) with ordering {:?} on {:?} (size={})",
access.description(None, None),
&atomic,
place.ptr(),
size.bytes()
);
let current_span = this.machine.current_span();
// Perform the atomic operation.
data_race.maybe_perform_sync_operation(
&this.machine.threads,
current_span,
|index, mut thread_clocks| {
for (mem_clocks_range, mem_clocks) in
alloc_meta.alloc_ranges.borrow_mut().iter_mut(base_offset, size)
{
if let Err(DataRace) = op(mem_clocks, &mut thread_clocks, index, atomic) {
mem::drop(thread_clocks);
return VClockAlloc::report_data_race(
data_race,
&this.machine.threads,
mem_clocks,
access,
place.layout.size,
interpret::Pointer::new(
alloc_id,
Size::from_bytes(mem_clocks_range.start),
),
None,
)
.map(|_| true);
}
}
// This conservatively assumes all operations have release semantics
interp_ok(true)
},
)?;
// Log changes to atomic memory.
if tracing::enabled!(tracing::Level::TRACE) {
for (_offset, mem_clocks) in alloc_meta.alloc_ranges.borrow().iter(base_offset, size) {
trace!(
"Updated atomic memory({:?}, size={}) to {:#?}",
place.ptr(),
size.bytes(),
mem_clocks.atomic_ops
);
}
}
interp_ok(())
}
}
impl GlobalState {
/// Create a new global state, setup with just thread-id=0
/// advanced to timestamp = 1.
pub fn new(config: &MiriConfig) -> Self {
let mut global_state = GlobalState {
multi_threaded: Cell::new(false),
ongoing_action_data_race_free: Cell::new(false),
vector_clocks: RefCell::new(IndexVec::new()),
vector_info: RefCell::new(IndexVec::new()),
thread_info: RefCell::new(IndexVec::new()),
reuse_candidates: RefCell::new(FxHashSet::default()),
last_sc_fence: RefCell::new(VClock::default()),
last_sc_write_per_thread: RefCell::new(VClock::default()),
track_outdated_loads: config.track_outdated_loads,
};
// Setup the main-thread since it is not explicitly created:
// uses vector index and thread-id 0.
let index = global_state.vector_clocks.get_mut().push(ThreadClockSet::default());
global_state.vector_info.get_mut().push(ThreadId::MAIN_THREAD);
global_state
.thread_info
.get_mut()
.push(ThreadExtraState { vector_index: Some(index), termination_vector_clock: None });
global_state
}
// We perform data race detection when there are more than 1 active thread
// and we have not temporarily disabled race detection to perform something
// data race free
fn race_detecting(&self) -> bool {
self.multi_threaded.get() && !self.ongoing_action_data_race_free.get()
}
pub fn ongoing_action_data_race_free(&self) -> bool {
self.ongoing_action_data_race_free.get()
}
// Try to find vector index values that can potentially be re-used
// by a new thread instead of a new vector index being created.
fn find_vector_index_reuse_candidate(&self) -> Option<VectorIdx> {
let mut reuse = self.reuse_candidates.borrow_mut();
let vector_clocks = self.vector_clocks.borrow();
for &candidate in reuse.iter() {
let target_timestamp = vector_clocks[candidate].clock[candidate];
if vector_clocks.iter_enumerated().all(|(clock_idx, clock)| {
// The thread happens before the clock, and hence cannot report
// a data-race with this the candidate index.
let no_data_race = clock.clock[candidate] >= target_timestamp;
// The vector represents a thread that has terminated and hence cannot
// report a data-race with the candidate index.
let vector_terminated = reuse.contains(&clock_idx);
// The vector index cannot report a race with the candidate index
// and hence allows the candidate index to be re-used.
no_data_race || vector_terminated
}) {
// All vector clocks for each vector index are equal to
// the target timestamp, and the thread is known to have
// terminated, therefore this vector clock index cannot
// report any more data-races.
assert!(reuse.remove(&candidate));
return Some(candidate);
}
}
None
}
// Hook for thread creation, enabled multi-threaded execution and marks
// the current thread timestamp as happening-before the current thread.
#[inline]
pub fn thread_created(
&mut self,
thread_mgr: &ThreadManager<'_>,
thread: ThreadId,
current_span: Span,
) {
let current_index = self.active_thread_index(thread_mgr);
// Enable multi-threaded execution, there are now at least two threads
// so data-races are now possible.
self.multi_threaded.set(true);
// Load and setup the associated thread metadata
let mut thread_info = self.thread_info.borrow_mut();
thread_info.ensure_contains_elem(thread, Default::default);
// Assign a vector index for the thread, attempting to re-use an old
// vector index that can no longer report any data-races if possible.
let created_index = if let Some(reuse_index) = self.find_vector_index_reuse_candidate() {
// Now re-configure the re-use candidate, increment the clock
// for the new sync use of the vector.
let vector_clocks = self.vector_clocks.get_mut();
vector_clocks[reuse_index].increment_clock(reuse_index, current_span);
// Locate the old thread the vector was associated with and update
// it to represent the new thread instead.
let vector_info = self.vector_info.get_mut();
let old_thread = vector_info[reuse_index];
vector_info[reuse_index] = thread;
// Mark the thread the vector index was associated with as no longer
// representing a thread index.
thread_info[old_thread].vector_index = None;
reuse_index
} else {
// No vector re-use candidates available, instead create
// a new vector index.
let vector_info = self.vector_info.get_mut();
vector_info.push(thread)
};
trace!("Creating thread = {:?} with vector index = {:?}", thread, created_index);
// Mark the chosen vector index as in use by the thread.
thread_info[thread].vector_index = Some(created_index);
// Create a thread clock set if applicable.
let vector_clocks = self.vector_clocks.get_mut();
if created_index == vector_clocks.next_index() {
vector_clocks.push(ThreadClockSet::default());
}
// Now load the two clocks and configure the initial state.
let (current, created) = vector_clocks.pick2_mut(current_index, created_index);
// Join the created with current, since the current threads
// previous actions happen-before the created thread.
created.join_with(current);
// Advance both threads after the synchronized operation.
// Both operations are considered to have release semantics.
current.increment_clock(current_index, current_span);
created.increment_clock(created_index, current_span);
}
/// Hook on a thread join to update the implicit happens-before relation between the joined
/// thread (the joinee, the thread that someone waited on) and the current thread (the joiner,
/// the thread who was waiting).
#[inline]
pub fn thread_joined(&mut self, threads: &ThreadManager<'_>, joinee: ThreadId) {
let thread_info = self.thread_info.borrow();
let thread_info = &thread_info[joinee];
// Load the associated vector clock for the terminated thread.
let join_clock = thread_info
.termination_vector_clock
.as_ref()
.expect("joined with thread but thread has not terminated");
// Acquire that into the current thread.
self.acquire_clock(join_clock, threads);
// Check the number of live threads, if the value is 1
// then test for potentially disabling multi-threaded execution.
// This has to happen after `acquire_clock`, otherwise there'll always
// be some thread that has not synchronized yet.
if let Some(current_index) = thread_info.vector_index {
if threads.get_live_thread_count() == 1 {
let vector_clocks = self.vector_clocks.get_mut();
// May potentially be able to disable multi-threaded execution.
let current_clock = &vector_clocks[current_index];
if vector_clocks
.iter_enumerated()
.all(|(idx, clocks)| clocks.clock[idx] <= current_clock.clock[idx])
{
// All thread terminations happen-before the current clock
// therefore no data-races can be reported until a new thread
// is created, so disable multi-threaded execution.
self.multi_threaded.set(false);
}
}
}
}
/// On thread termination, the vector-clock may re-used
/// in the future once all remaining thread-clocks catch
/// up with the time index of the terminated thread.
/// This assigns thread termination with a unique index
/// which will be used to join the thread
/// This should be called strictly before any calls to
/// `thread_joined`.
#[inline]
pub fn thread_terminated(&mut self, thread_mgr: &ThreadManager<'_>) {
let current_thread = thread_mgr.active_thread();
let current_index = self.active_thread_index(thread_mgr);
// Store the terminaion clock.
let terminaion_clock = self.release_clock(thread_mgr, |clock| clock.clone());
self.thread_info.get_mut()[current_thread].termination_vector_clock =
Some(terminaion_clock);
// Add this thread's clock index as a candidate for re-use.
let reuse = self.reuse_candidates.get_mut();
reuse.insert(current_index);
}
/// Attempt to perform a synchronized operation, this
/// will perform no operation if multi-threading is
/// not currently enabled.
/// Otherwise it will increment the clock for the current
/// vector before and after the operation for data-race
/// detection between any happens-before edges the
/// operation may create.
fn maybe_perform_sync_operation<'tcx>(
&self,
thread_mgr: &ThreadManager<'_>,
current_span: Span,
op: impl FnOnce(VectorIdx, RefMut<'_, ThreadClockSet>) -> InterpResult<'tcx, bool>,
) -> InterpResult<'tcx> {
if self.multi_threaded.get() {
let (index, clocks) = self.active_thread_state_mut(thread_mgr);
if op(index, clocks)? {
let (_, mut clocks) = self.active_thread_state_mut(thread_mgr);
clocks.increment_clock(index, current_span);
}
}
interp_ok(())
}
/// Internal utility to identify a thread stored internally
/// returns the id and the name for better diagnostics.
fn print_thread_metadata(&self, thread_mgr: &ThreadManager<'_>, vector: VectorIdx) -> String {
let thread = self.vector_info.borrow()[vector];
let thread_name = thread_mgr.get_thread_display_name(thread);
format!("thread `{thread_name}`")
}
/// Acquire the given clock into the current thread, establishing synchronization with
/// the moment when that clock snapshot was taken via `release_clock`.
/// As this is an acquire operation, the thread timestamp is not
/// incremented.
pub fn acquire_clock<'tcx>(&self, clock: &VClock, threads: &ThreadManager<'tcx>) {
let thread = threads.active_thread();
let (_, mut clocks) = self.thread_state_mut(thread);
clocks.clock.join(clock);
}
/// Calls the given closure with the "release" clock of the current thread.
/// Other threads can acquire this clock in the future to establish synchronization
/// with this program point.
pub fn release_clock<'tcx, R>(
&self,
threads: &ThreadManager<'tcx>,
callback: impl FnOnce(&VClock) -> R,
) -> R {
let thread = threads.active_thread();
let span = threads.active_thread_ref().current_span();
let (index, mut clocks) = self.thread_state_mut(thread);
let r = callback(&clocks.clock);
// Increment the clock, so that all following events cannot be confused with anything that
// occurred before the release. Crucially, the callback is invoked on the *old* clock!
clocks.increment_clock(index, span);
r
}
fn thread_index(&self, thread: ThreadId) -> VectorIdx {
self.thread_info.borrow()[thread].vector_index.expect("thread has no assigned vector")
}
/// Load the vector index used by the given thread as well as the set of vector clocks
/// used by the thread.
#[inline]
fn thread_state_mut(&self, thread: ThreadId) -> (VectorIdx, RefMut<'_, ThreadClockSet>) {
let index = self.thread_index(thread);
let ref_vector = self.vector_clocks.borrow_mut();
let clocks = RefMut::map(ref_vector, |vec| &mut vec[index]);
(index, clocks)
}
/// Load the vector index used by the given thread as well as the set of vector clocks
/// used by the thread.
#[inline]
fn thread_state(&self, thread: ThreadId) -> (VectorIdx, Ref<'_, ThreadClockSet>) {
let index = self.thread_index(thread);
let ref_vector = self.vector_clocks.borrow();
let clocks = Ref::map(ref_vector, |vec| &vec[index]);
(index, clocks)
}
/// Load the current vector clock in use and the current set of thread clocks
/// in use for the vector.
#[inline]
pub(super) fn active_thread_state(
&self,
thread_mgr: &ThreadManager<'_>,
) -> (VectorIdx, Ref<'_, ThreadClockSet>) {
self.thread_state(thread_mgr.active_thread())
}
/// Load the current vector clock in use and the current set of thread clocks
/// in use for the vector mutably for modification.
#[inline]
pub(super) fn active_thread_state_mut(
&self,
thread_mgr: &ThreadManager<'_>,
) -> (VectorIdx, RefMut<'_, ThreadClockSet>) {
self.thread_state_mut(thread_mgr.active_thread())
}
/// Return the current thread, should be the same
/// as the data-race active thread.
#[inline]
fn active_thread_index(&self, thread_mgr: &ThreadManager<'_>) -> VectorIdx {
let active_thread_id = thread_mgr.active_thread();
self.thread_index(active_thread_id)
}
// SC ATOMIC STORE rule in the paper.
pub(super) fn sc_write(&self, thread_mgr: &ThreadManager<'_>) {
let (index, clocks) = self.active_thread_state(thread_mgr);
self.last_sc_write_per_thread.borrow_mut().set_at_index(&clocks.clock, index);
}
// SC ATOMIC READ rule in the paper.
pub(super) fn sc_read(&self, thread_mgr: &ThreadManager<'_>) {
let (.., mut clocks) = self.active_thread_state_mut(thread_mgr);
clocks.read_seqcst.join(&self.last_sc_fence.borrow());
}
}