Use proper atomic rmw for {mutex, rwlock, cond, srwlock}_get_or_create_id

Author: cbeuw

src/data_race.rs

@@ -441,21 +441,33 @@ impl MemoryCellClocks {
 /// Evaluation context extensions.
 impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for MiriEvalContext<'mir, 'tcx> {}
 pub trait EvalContextExt<'mir, 'tcx: 'mir>: MiriEvalContextExt<'mir, 'tcx> {
-    /// Atomic variant of read_scalar_at_offset.
-    fn read_scalar_at_offset_atomic(
+    /// Calculates the MPlaceTy given the offset and layout of an access on an operand
+    fn offset_and_layout_to_place(
         &self,
         op: &OpTy<'tcx, Tag>,
         offset: u64,
         layout: TyAndLayout<'tcx>,
-        atomic: AtomicReadOp,
-    ) -> InterpResult<'tcx, ScalarMaybeUninit<Tag>> {
+    ) -> InterpResult<'tcx, MPlaceTy<'tcx, Tag>> {
         let this = self.eval_context_ref();
         let op_place = this.deref_operand(op)?;
         let offset = Size::from_bytes(offset);
 
-        // Ensure that the following read at an offset is within bounds.
+        // Ensure that the access is within bounds.
         assert!(op_place.layout.size >= offset + layout.size);
         let value_place = op_place.offset(offset, MemPlaceMeta::None, layout, this)?;
+        Ok(value_place)
+    }
+
+    /// Atomic variant of read_scalar_at_offset.
+    fn read_scalar_at_offset_atomic(
+        &self,
+        op: &OpTy<'tcx, Tag>,
+        offset: u64,
+        layout: TyAndLayout<'tcx>,
+        atomic: AtomicReadOp,
+    ) -> InterpResult<'tcx, ScalarMaybeUninit<Tag>> {
+        let this = self.eval_context_ref();
+        let value_place = this.offset_and_layout_to_place(op, offset, layout)?;
         this.read_scalar_atomic(&value_place, atomic)
     }
 
@@ -469,12 +481,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: MiriEvalContextExt<'mir, 'tcx> {
         atomic: AtomicWriteOp,
     ) -> InterpResult<'tcx> {
         let this = self.eval_context_mut();
-        let op_place = this.deref_operand(op)?;
-        let offset = Size::from_bytes(offset);
-
-        // Ensure that the following read at an offset is within bounds.
-        assert!(op_place.layout.size >= offset + layout.size);
-        let value_place = op_place.offset(offset, MemPlaceMeta::None, layout, this)?;
+        let value_place = this.offset_and_layout_to_place(op, offset, layout)?;
         this.write_scalar_atomic(value.into(), &value_place, atomic)
     }
 

src/shims/posix/sync.rs

@@ -112,15 +112,23 @@ fn mutex_get_or_create_id<'mir, 'tcx: 'mir>(
     ecx: &mut MiriEvalContext<'mir, 'tcx>,
     mutex_op: &OpTy<'tcx, Tag>,
 ) -> InterpResult<'tcx, MutexId> {
-    let id = mutex_get_id(ecx, mutex_op)?.to_u32()?;
-    if id == 0 {
-        // 0 is a default value and also not a valid mutex id. Need to allocate
-        // a new mutex.
+    let value_place = ecx.offset_and_layout_to_place(mutex_op, 4, ecx.machine.layouts.u32)?;
+    let (old, success) = ecx
+        .atomic_compare_exchange_scalar(
+            &value_place,
+            &ImmTy::from_uint(0u32, ecx.machine.layouts.u32),
+            ecx.mutex_next_id().to_u32_scalar().into(),
+            AtomicRwOp::Relaxed,
+            AtomicReadOp::Relaxed,
+            false,
+        )?
+        .to_scalar_pair()?;
+
+    if success.to_bool().expect("compare_exchange's second return value is a bool") {
         let id = ecx.mutex_create();
-        mutex_set_id(ecx, mutex_op, id.to_u32_scalar())?;
         Ok(id)
     } else {
-        Ok(MutexId::from_u32(id))
+        Ok(MutexId::from_u32(old.to_u32().expect("layout is u32")))
     }
 }
 
@@ -156,15 +164,23 @@ fn rwlock_get_or_create_id<'mir, 'tcx: 'mir>(
     ecx: &mut MiriEvalContext<'mir, 'tcx>,
     rwlock_op: &OpTy<'tcx, Tag>,
 ) -> InterpResult<'tcx, RwLockId> {
-    let id = rwlock_get_id(ecx, rwlock_op)?.to_u32()?;
-    if id == 0 {
-        // 0 is a default value and also not a valid rwlock id. Need to allocate
-        // a new read-write lock.
+    let value_place = ecx.offset_and_layout_to_place(rwlock_op, 4, ecx.machine.layouts.u32)?;
+    let (old, success) = ecx
+        .atomic_compare_exchange_scalar(
+            &value_place,
+            &ImmTy::from_uint(0u32, ecx.machine.layouts.u32),
+            ecx.rwlock_next_id().to_u32_scalar().into(),
+            AtomicRwOp::Relaxed,
+            AtomicReadOp::Relaxed,
+            false,
+        )?
+        .to_scalar_pair()?;
+
+    if success.to_bool().expect("compare_exchange's second return value is a bool") {
         let id = ecx.rwlock_create();
-        rwlock_set_id(ecx, rwlock_op, id.to_u32_scalar())?;
         Ok(id)
     } else {
-        Ok(RwLockId::from_u32(id))
+        Ok(RwLockId::from_u32(old.to_u32().expect("layout is u32")))
     }
 }
 
@@ -228,15 +244,24 @@ fn cond_get_or_create_id<'mir, 'tcx: 'mir>(
     ecx: &mut MiriEvalContext<'mir, 'tcx>,
     cond_op: &OpTy<'tcx, Tag>,
 ) -> InterpResult<'tcx, CondvarId> {
-    let id = cond_get_id(ecx, cond_op)?.to_u32()?;
-    if id == 0 {
-        // 0 is a default value and also not a valid conditional variable id.
-        // Need to allocate a new id.
+    let value_place = ecx.offset_and_layout_to_place(cond_op, 4, ecx.machine.layouts.u32)?;
+
+    let (old, success) = ecx
+        .atomic_compare_exchange_scalar(
+            &value_place,
+            &ImmTy::from_uint(0u32, ecx.machine.layouts.u32),
+            ecx.condvar_next_id().to_u32_scalar().into(),
+            AtomicRwOp::Relaxed,
+            AtomicReadOp::Relaxed,
+            false,
+        )?
+        .to_scalar_pair()?;
+
+    if success.to_bool().expect("compare_exchange's second return value is a bool") {
         let id = ecx.condvar_create();
-        cond_set_id(ecx, cond_op, id.to_u32_scalar())?;
         Ok(id)
     } else {
-        Ok(CondvarId::from_u32(id))
+        Ok(CondvarId::from_u32(old.to_u32().expect("layout is u32")))
     }
 }
 

src/shims/windows/sync.rs

@@ -7,15 +7,24 @@ fn srwlock_get_or_create_id<'mir, 'tcx: 'mir>(
     ecx: &mut MiriEvalContext<'mir, 'tcx>,
     lock_op: &OpTy<'tcx, Tag>,
 ) -> InterpResult<'tcx, RwLockId> {
-    let id = ecx.read_scalar_at_offset(lock_op, 0, ecx.machine.layouts.u32)?.to_u32()?;
-    if id == 0 {
-        // 0 is a default value and also not a valid rwlock id. Need to allocate
-        // a new rwlock.
+    let value_place = ecx.offset_and_layout_to_place(lock_op, 0, ecx.machine.layouts.u32)?;
+
+    let (old, success) = ecx
+        .atomic_compare_exchange_scalar(
+            &value_place,
+            &ImmTy::from_uint(0u32, ecx.machine.layouts.u32),
+            ecx.rwlock_next_id().to_u32_scalar().into(),
+            AtomicRwOp::AcqRel,
+            AtomicReadOp::Acquire,
+            false,
+        )?
+        .to_scalar_pair()?;
+
+    if success.to_bool().expect("compare_exchange's second return value is a bool") {
         let id = ecx.rwlock_create();
-        ecx.write_scalar_at_offset(lock_op, 0, id.to_u32_scalar(), ecx.machine.layouts.u32)?;
         Ok(id)
     } else {
-        Ok(RwLockId::from_u32(id))
+        Ok(RwLockId::from_u32(old.to_u32().expect("layout is u32")))
     }
 }
 

src/sync.rs

@@ -208,6 +208,13 @@ trait EvalContextExtPriv<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
 // situations.
 impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
 pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> {
+    #[inline]
+    /// Peek the id of the next mutex
+    fn mutex_next_id(&self) -> MutexId {
+        let this = self.eval_context_ref();
+        this.machine.threads.sync.mutexes.next_index()
+    }
+
     #[inline]
     /// Create state for a new mutex.
     fn mutex_create(&mut self) -> MutexId {
@@ -290,6 +297,13 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         this.block_thread(thread);
     }
 
+    #[inline]
+    /// Peek the id of the next read write lock
+    fn rwlock_next_id(&self) -> RwLockId {
+        let this = self.eval_context_ref();
+        this.machine.threads.sync.rwlocks.next_index()
+    }
+
     #[inline]
     /// Create state for a new read write lock.
     fn rwlock_create(&mut self) -> RwLockId {
@@ -438,6 +452,13 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         this.block_thread(writer);
     }
 
+    #[inline]
+    /// Peek the id of the next Condvar
+    fn condvar_next_id(&self) -> CondvarId {
+        let this = self.eval_context_ref();
+        this.machine.threads.sync.condvars.next_index()
+    }
+
     #[inline]
     /// Create state for a new conditional variable.
     fn condvar_create(&mut self) -> CondvarId {