also test pthread_mutex/rwlock directly

turns out one of the synchronizations in rwlock_writer_unlock is unnecessary

src/tools/miri/src/concurrency/sync.rs

@@ -110,6 +110,7 @@ struct RwLock {
     /// must load the clock of the last write and must not
     /// add happens-before orderings between shared reader
     /// locks.
+    /// This is only relevant when there is an active reader.
     data_race_reader: VClock,
 }
 
@@ -485,6 +486,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
             Entry::Vacant(_) => return false, // we did not even own this lock
         }
         if let Some(data_race) = &this.machine.data_race {
+            // Add this to the shared-release clock of all concurrent readers.
             data_race.validate_lock_release_shared(
                 &mut rwlock.data_race_reader,
                 reader,
@@ -539,20 +541,13 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
             }
             rwlock.writer = None;
             trace!("rwlock_writer_unlock: {:?} unlocked by {:?}", id, expected_writer);
-            // Release memory to both reader and writer vector clocks
-            //  since this writer happens-before both the union of readers once they are finished
-            //  and the next writer
+            // Release memory to next lock holder.
             if let Some(data_race) = &this.machine.data_race {
                 data_race.validate_lock_release(
                     &mut rwlock.data_race,
                     current_writer,
                     current_span,
                 );
-                data_race.validate_lock_release(
-                    &mut rwlock.data_race_reader,
-                    current_writer,
-                    current_span,
-                );
             }
             // The thread was a writer.
             //

src/tools/miri/tests/pass-dep/shims/pthread-sync.rs

@@ -1,24 +1,34 @@
 //@ignore-target-windows: No libc on Windows
+// We use `yield` to test specific interleavings, so disable automatic preemption.
+//@compile-flags: -Zmiri-preemption-rate=0
+#![feature(sync_unsafe_cell)]
+
+use std::cell::SyncUnsafeCell;
+use std::thread;
+use std::{mem, ptr};
 
 fn main() {
     test_mutex_libc_init_recursive();
     test_mutex_libc_init_normal();
     test_mutex_libc_init_errorcheck();
     test_rwlock_libc_static_initializer();
-
     #[cfg(target_os = "linux")]
     test_mutex_libc_static_initializer_recursive();
+
+    test_mutex();
+    check_rwlock_write();
+    check_rwlock_read_no_deadlock();
 }
 
 fn test_mutex_libc_init_recursive() {
     unsafe {
-        let mut attr: libc::pthread_mutexattr_t = std::mem::zeroed();
+        let mut attr: libc::pthread_mutexattr_t = mem::zeroed();
         assert_eq!(libc::pthread_mutexattr_init(&mut attr as *mut _), 0);
         assert_eq!(
             libc::pthread_mutexattr_settype(&mut attr as *mut _, libc::PTHREAD_MUTEX_RECURSIVE),
             0,
         );
-        let mut mutex: libc::pthread_mutex_t = std::mem::zeroed();
+        let mut mutex: libc::pthread_mutex_t = mem::zeroed();
         assert_eq!(libc::pthread_mutex_init(&mut mutex as *mut _, &mut attr as *mut _), 0);
         assert_eq!(libc::pthread_mutex_lock(&mut mutex as *mut _), 0);
         assert_eq!(libc::pthread_mutex_trylock(&mut mutex as *mut _), 0);
@@ -36,7 +46,7 @@ fn test_mutex_libc_init_recursive() {
 
 fn test_mutex_libc_init_normal() {
     unsafe {
-        let mut mutexattr: libc::pthread_mutexattr_t = std::mem::zeroed();
+        let mut mutexattr: libc::pthread_mutexattr_t = mem::zeroed();
         assert_eq!(
             libc::pthread_mutexattr_settype(&mut mutexattr as *mut _, 0x12345678),
             libc::EINVAL,
@@ -45,7 +55,7 @@ fn test_mutex_libc_init_normal() {
             libc::pthread_mutexattr_settype(&mut mutexattr as *mut _, libc::PTHREAD_MUTEX_NORMAL),
             0,
         );
-        let mut mutex: libc::pthread_mutex_t = std::mem::zeroed();
+        let mut mutex: libc::pthread_mutex_t = mem::zeroed();
         assert_eq!(libc::pthread_mutex_init(&mut mutex as *mut _, &mutexattr as *const _), 0);
         assert_eq!(libc::pthread_mutex_lock(&mut mutex as *mut _), 0);
         assert_eq!(libc::pthread_mutex_trylock(&mut mutex as *mut _), libc::EBUSY);
@@ -58,7 +68,7 @@ fn test_mutex_libc_init_normal() {
 
 fn test_mutex_libc_init_errorcheck() {
     unsafe {
-        let mut mutexattr: libc::pthread_mutexattr_t = std::mem::zeroed();
+        let mut mutexattr: libc::pthread_mutexattr_t = mem::zeroed();
         assert_eq!(
             libc::pthread_mutexattr_settype(
                 &mut mutexattr as *mut _,
@@ -66,7 +76,7 @@ fn test_mutex_libc_init_errorcheck() {
             ),
             0,
         );
-        let mut mutex: libc::pthread_mutex_t = std::mem::zeroed();
+        let mut mutex: libc::pthread_mutex_t = mem::zeroed();
         assert_eq!(libc::pthread_mutex_init(&mut mutex as *mut _, &mutexattr as *const _), 0);
         assert_eq!(libc::pthread_mutex_lock(&mut mutex as *mut _), 0);
         assert_eq!(libc::pthread_mutex_trylock(&mut mutex as *mut _), libc::EBUSY);
@@ -98,6 +108,111 @@ fn test_mutex_libc_static_initializer_recursive() {
     }
 }
 
+struct SendPtr<T> {
+    ptr: *mut T,
+}
+unsafe impl<T> Send for SendPtr<T> {}
+impl<T> Copy for SendPtr<T> {}
+impl<T> Clone for SendPtr<T> {
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+
+fn test_mutex() {
+    // Specifically *not* using `Arc` to make sure there is no synchronization apart from the mutex.
+    unsafe {
+        let data = SyncUnsafeCell::new((libc::PTHREAD_MUTEX_INITIALIZER, 0));
+        let ptr = SendPtr { ptr: data.get() };
+        let mut threads = Vec::new();
+
+        for _ in 0..3 {
+            let thread = thread::spawn(move || {
+                let ptr = ptr; // circumvent per-field closure capture
+                let mutexptr = ptr::addr_of_mut!((*ptr.ptr).0);
+                assert_eq!(libc::pthread_mutex_lock(mutexptr), 0);
+                thread::yield_now();
+                (*ptr.ptr).1 += 1;
+                assert_eq!(libc::pthread_mutex_unlock(mutexptr), 0);
+            });
+            threads.push(thread);
+        }
+
+        for thread in threads {
+            thread.join().unwrap();
+        }
+
+        let mutexptr = ptr::addr_of_mut!((*ptr.ptr).0);
+        assert_eq!(libc::pthread_mutex_trylock(mutexptr), 0);
+        assert_eq!((*ptr.ptr).1, 3);
+    }
+}
+
+fn check_rwlock_write() {
+    unsafe {
+        let data = SyncUnsafeCell::new((libc::PTHREAD_RWLOCK_INITIALIZER, 0));
+        let ptr = SendPtr { ptr: data.get() };
+        let mut threads = Vec::new();
+
+        for _ in 0..3 {
+            let thread = thread::spawn(move || {
+                let ptr = ptr; // circumvent per-field closure capture
+                let rwlockptr = ptr::addr_of_mut!((*ptr.ptr).0);
+                assert_eq!(libc::pthread_rwlock_wrlock(rwlockptr), 0);
+                thread::yield_now();
+                (*ptr.ptr).1 += 1;
+                assert_eq!(libc::pthread_rwlock_unlock(rwlockptr), 0);
+            });
+            threads.push(thread);
+
+            let readthread = thread::spawn(move || {
+                let ptr = ptr; // circumvent per-field closure capture
+                let rwlockptr = ptr::addr_of_mut!((*ptr.ptr).0);
+                assert_eq!(libc::pthread_rwlock_rdlock(rwlockptr), 0);
+                thread::yield_now();
+                let val = (*ptr.ptr).1;
+                assert!(val >= 0 && val <= 3);
+                assert_eq!(libc::pthread_rwlock_unlock(rwlockptr), 0);
+            });
+            threads.push(readthread);
+        }
+
+        for thread in threads {
+            thread.join().unwrap();
+        }
+
+        let rwlockptr = ptr::addr_of_mut!((*ptr.ptr).0);
+        assert_eq!(libc::pthread_rwlock_tryrdlock(rwlockptr), 0);
+        assert_eq!((*ptr.ptr).1, 3);
+    }
+}
+
+fn check_rwlock_read_no_deadlock() {
+    unsafe {
+        let l1 = SyncUnsafeCell::new(libc::PTHREAD_RWLOCK_INITIALIZER);
+        let l1 = SendPtr { ptr: l1.get() };
+        let l2 = SyncUnsafeCell::new(libc::PTHREAD_RWLOCK_INITIALIZER);
+        let l2 = SendPtr { ptr: l2.get() };
+
+        // acquire l1 and hold it until after the other thread is done
+        assert_eq!(libc::pthread_rwlock_rdlock(l1.ptr), 0);
+        let handle = thread::spawn(move || {
+            let l1 = l1; // circumvent per-field closure capture
+            let l2 = l2; // circumvent per-field closure capture
+            // acquire l2 before the other thread
+            assert_eq!(libc::pthread_rwlock_rdlock(l2.ptr), 0);
+            thread::yield_now();
+            assert_eq!(libc::pthread_rwlock_rdlock(l1.ptr), 0);
+            thread::yield_now();
+            assert_eq!(libc::pthread_rwlock_unlock(l1.ptr), 0);
+            assert_eq!(libc::pthread_rwlock_unlock(l2.ptr), 0);
+        });
+        thread::yield_now();
+        assert_eq!(libc::pthread_rwlock_rdlock(l2.ptr), 0);
+        handle.join().unwrap();
+    }
+}
+
 // std::sync::RwLock does not even used pthread_rwlock any more.
 // Do some smoke testing of the API surface.
 fn test_rwlock_libc_static_initializer() {

src/tools/miri/tests/pass/concurrency/sync.rs

@@ -1,6 +1,7 @@
 //@revisions: stack tree
 //@[tree]compile-flags: -Zmiri-tree-borrows
-//@compile-flags: -Zmiri-disable-isolation -Zmiri-strict-provenance
+// We use `yield` to test specific interleavings, so disable automatic preemption.
+//@compile-flags: -Zmiri-disable-isolation -Zmiri-strict-provenance -Zmiri-preemption-rate=0
 
 use std::sync::{Arc, Barrier, Condvar, Mutex, Once, RwLock};
 use std::thread;
@@ -119,13 +120,25 @@ fn check_rwlock_write() {
     let mut threads = Vec::new();
 
     for _ in 0..3 {
-        let data = Arc::clone(&data);
-        let thread = thread::spawn(move || {
-            let mut data = data.write().unwrap();
-            thread::yield_now();
-            *data += 1;
+        let thread = thread::spawn({
+            let data = Arc::clone(&data);
+            move || {
+                let mut data = data.write().unwrap();
+                thread::yield_now();
+                *data += 1;
+            }
         });
         threads.push(thread);
+
+        let readthread = thread::spawn({
+            let data = Arc::clone(&data);
+            move || {
+                let data = data.read().unwrap();
+                thread::yield_now();
+                assert!(*data >= 0 && *data <= 3);
+            }
+        });
+        threads.push(readthread);
     }
 
     for thread in threads {
@@ -144,8 +157,10 @@ fn check_rwlock_read_no_deadlock() {
 
     let l1_copy = Arc::clone(&l1);
     let l2_copy = Arc::clone(&l2);
+    // acquire l1 and hold it until after the other thread is done
     let _guard1 = l1.read().unwrap();
     let handle = thread::spawn(move || {
+        // acquire l2 before the other thread
         let _guard2 = l2_copy.read().unwrap();
         thread::yield_now();
         let _guard1 = l1_copy.read().unwrap();