From 1effdc091b441c4b1ada4327c1422cd360f80f98 Mon Sep 17 00:00:00 2001
From: Ian Gudger <igudger@google.com>
Date: Tue, 21 Jan 2020 16:59:24 -0800
Subject: TMutex based on sync.Mutex.

Updates #231

PiperOrigin-RevId: 290854399
---
 pkg/sync/BUILD            |  2 ++
 pkg/sync/tmutex_test.go   | 71 +++++++++++++++++++++++++++++++++++++++++++++++
 pkg/sync/tmutex_unsafe.go | 49 ++++++++++++++++++++++++++++++++
 3 files changed, 122 insertions(+)
 create mode 100644 pkg/sync/tmutex_test.go
 create mode 100644 pkg/sync/tmutex_unsafe.go

(limited to 'pkg/sync')

diff --git a/pkg/sync/BUILD b/pkg/sync/BUILD
index e8cd16b8f..97c4b3b1e 100644
--- a/pkg/sync/BUILD
+++ b/pkg/sync/BUILD
@@ -38,6 +38,7 @@ go_library(
         "race_unsafe.go",
         "seqcount.go",
         "syncutil.go",
+        "tmutex_unsafe.go",
     ],
     importpath = "gvisor.dev/gvisor/pkg/sync",
 )
@@ -48,6 +49,7 @@ go_test(
     srcs = [
         "downgradable_rwmutex_test.go",
         "seqcount_test.go",
+        "tmutex_test.go",
     ],
     embed = [":sync"],
 )
diff --git a/pkg/sync/tmutex_test.go b/pkg/sync/tmutex_test.go
new file mode 100644
index 000000000..c640bae23
--- /dev/null
+++ b/pkg/sync/tmutex_test.go
@@ -0,0 +1,71 @@
+// Copyright 2019 The gVisor Authors.
+//
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package sync
+
+import (
+	"sync"
+	"testing"
+	"unsafe"
+)
+
+// TestStructSize verifies that syncMutex's size hasn't drifted from the
+// standard library's version.
+//
+// The correctness of this package relies on these remaining in sync.
+func TestStructSize(t *testing.T) {
+	const (
+		got  = unsafe.Sizeof(syncMutex{})
+		want = unsafe.Sizeof(sync.Mutex{})
+	)
+	if got != want {
+		t.Errorf("got sizeof(syncMutex) = %d, want = sizeof(sync.Mutex) = %d", got, want)
+	}
+}
+
+// TestFieldValues verifies that the semantics of syncMutex.state from the
+// standard library's implementation.
+//
+// The correctness of this package relies on these remaining in sync.
+func TestFieldValues(t *testing.T) {
+	var m TMutex
+	m.Lock()
+	if got := *m.state(); got != mutexLocked {
+		t.Errorf("got locked sync.Mutex.state = %d, want = %d", got, mutexLocked)
+	}
+	m.Unlock()
+	if got := *m.state(); got != mutexUnlocked {
+		t.Errorf("got unlocked sync.Mutex.state = %d, want = %d", got, mutexUnlocked)
+	}
+}
+
+func TestDoubleTryLock(t *testing.T) {
+	var m TMutex
+	if !m.TryLock() {
+		t.Fatal("failed to aquire lock")
+	}
+	if m.TryLock() {
+		t.Fatal("unexpectedly succeeded in aquiring locked mutex")
+	}
+}
+
+func TestTryLockAfterLock(t *testing.T) {
+	var m TMutex
+	m.Lock()
+	if m.TryLock() {
+		t.Fatal("unexpectedly succeeded in aquiring locked mutex")
+	}
+}
+
+func TestTryLockUnlock(t *testing.T) {
+	var m TMutex
+	if !m.TryLock() {
+		t.Fatal("failed to aquire lock")
+	}
+	m.Unlock()
+	if !m.TryLock() {
+		t.Fatal("failed to aquire lock after unlock")
+	}
+}
diff --git a/pkg/sync/tmutex_unsafe.go b/pkg/sync/tmutex_unsafe.go
new file mode 100644
index 000000000..3c32f8371
--- /dev/null
+++ b/pkg/sync/tmutex_unsafe.go
@@ -0,0 +1,49 @@
+// Copyright 2019 The gVisor Authors.
+//
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build go1.13
+// +build !go1.15
+
+// When updating the build constraint (above), check that syncMutex matches the
+// standard library sync.Mutex definition.
+
+package sync
+
+import (
+	"sync"
+	"sync/atomic"
+	"unsafe"
+)
+
+// TMutex is a try lock.
+type TMutex struct {
+	sync.Mutex
+}
+
+type syncMutex struct {
+	state int32
+	sema  uint32
+}
+
+func (m *TMutex) state() *int32 {
+	return &(*syncMutex)(unsafe.Pointer(&m.Mutex)).state
+}
+
+const (
+	mutexUnlocked = 0
+	mutexLocked   = 1
+)
+
+// TryLock tries to aquire the mutex. It returns true if it succeeds and false
+// otherwise. TryLock does not block.
+func (m *TMutex) TryLock() bool {
+	if atomic.CompareAndSwapInt32(m.state(), mutexUnlocked, mutexLocked) {
+		if RaceEnabled {
+			RaceAcquire(unsafe.Pointer(&m.Mutex))
+		}
+		return true
+	}
+	return false
+}
-- 
cgit v1.2.3


From d0e75f2bef4e16356693987db6ae6bbdce749618 Mon Sep 17 00:00:00 2001
From: Ian Gudger <igudger@google.com>
Date: Tue, 21 Jan 2020 18:34:24 -0800
Subject: Add trylock support to DowngradableRWMutex.

Updates #231

PiperOrigin-RevId: 290868875
---
 pkg/sync/downgradable_rwmutex_test.go   | 55 ++++++++++++++++++++++++++
 pkg/sync/downgradable_rwmutex_unsafe.go | 68 +++++++++++++++++++++++++++++----
 2 files changed, 115 insertions(+), 8 deletions(-)

(limited to 'pkg/sync')

diff --git a/pkg/sync/downgradable_rwmutex_test.go b/pkg/sync/downgradable_rwmutex_test.go
index f04496bc5..b5cb28ec0 100644
--- a/pkg/sync/downgradable_rwmutex_test.go
+++ b/pkg/sync/downgradable_rwmutex_test.go
@@ -148,3 +148,58 @@ func TestDowngradableRWMutex(t *testing.T) {
 	HammerDowngradableRWMutex(10, 10, n)
 	HammerDowngradableRWMutex(10, 5, n)
 }
+
+func TestRWDoubleTryLock(t *testing.T) {
+	var m DowngradableRWMutex
+	if !m.TryLock() {
+		t.Fatal("failed to aquire lock")
+	}
+	if m.TryLock() {
+		t.Fatal("unexpectedly succeeded in aquiring locked mutex")
+	}
+}
+
+func TestRWTryLockAfterLock(t *testing.T) {
+	var m DowngradableRWMutex
+	m.Lock()
+	if m.TryLock() {
+		t.Fatal("unexpectedly succeeded in aquiring locked mutex")
+	}
+}
+
+func TestRWTryLockUnlock(t *testing.T) {
+	var m DowngradableRWMutex
+	if !m.TryLock() {
+		t.Fatal("failed to aquire lock")
+	}
+	m.Unlock()
+	if !m.TryLock() {
+		t.Fatal("failed to aquire lock after unlock")
+	}
+}
+
+func TestTryRLockAfterLock(t *testing.T) {
+	var m DowngradableRWMutex
+	m.Lock()
+	if m.TryRLock() {
+		t.Fatal("unexpectedly succeeded in aquiring locked mutex")
+	}
+}
+
+func TestTryLockAfterRLock(t *testing.T) {
+	var m DowngradableRWMutex
+	m.RLock()
+	if m.TryLock() {
+		t.Fatal("unexpectedly succeeded in aquiring locked mutex")
+	}
+}
+
+func TestDoubleTryRLock(t *testing.T) {
+	var m DowngradableRWMutex
+	if !m.TryRLock() {
+		t.Fatal("failed to aquire lock")
+	}
+	if !m.TryRLock() {
+		t.Fatal("failed to read aquire read locked lock")
+	}
+}
diff --git a/pkg/sync/downgradable_rwmutex_unsafe.go b/pkg/sync/downgradable_rwmutex_unsafe.go
index 9bb55cd3a..0d321f5e3 100644
--- a/pkg/sync/downgradable_rwmutex_unsafe.go
+++ b/pkg/sync/downgradable_rwmutex_unsafe.go
@@ -19,7 +19,6 @@
 package sync
 
 import (
-	"sync"
 	"sync/atomic"
 	"unsafe"
 )
@@ -30,18 +29,43 @@ func runtimeSemacquire(s *uint32)
 //go:linkname runtimeSemrelease sync.runtime_Semrelease
 func runtimeSemrelease(s *uint32, handoff bool, skipframes int)
 
-// DowngradableRWMutex is identical to sync.RWMutex, but adds the DowngradeLock
-// method.
+// DowngradableRWMutex is identical to sync.RWMutex, but adds the DowngradeLock,
+// TryLock and TryRLock methods.
 type DowngradableRWMutex struct {
-	w           sync.Mutex // held if there are pending writers
-	writerSem   uint32     // semaphore for writers to wait for completing readers
-	readerSem   uint32     // semaphore for readers to wait for completing writers
-	readerCount int32      // number of pending readers
-	readerWait  int32      // number of departing readers
+	w           TMutex // held if there are pending writers
+	writerSem   uint32 // semaphore for writers to wait for completing readers
+	readerSem   uint32 // semaphore for readers to wait for completing writers
+	readerCount int32  // number of pending readers
+	readerWait  int32  // number of departing readers
 }
 
 const rwmutexMaxReaders = 1 << 30
 
+// TryRLock locks rw for reading. It returns true if it succeeds and false
+// otherwise. It does not block.
+func (rw *DowngradableRWMutex) TryRLock() bool {
+	if RaceEnabled {
+		RaceDisable()
+	}
+	for {
+		rc := atomic.LoadInt32(&rw.readerCount)
+		if rc < 0 {
+			if RaceEnabled {
+				RaceEnable()
+			}
+			return false
+		}
+		if !atomic.CompareAndSwapInt32(&rw.readerCount, rc, rc+1) {
+			continue
+		}
+		if RaceEnabled {
+			RaceEnable()
+			RaceAcquire(unsafe.Pointer(&rw.readerSem))
+		}
+		return true
+	}
+}
+
 // RLock locks rw for reading.
 func (rw *DowngradableRWMutex) RLock() {
 	if RaceEnabled {
@@ -78,6 +102,34 @@ func (rw *DowngradableRWMutex) RUnlock() {
 	}
 }
 
+// TryLock locks rw for writing. It returns true if it succeeds and false
+// otherwise. It does not block.
+func (rw *DowngradableRWMutex) TryLock() bool {
+	if RaceEnabled {
+		RaceDisable()
+	}
+	// First, resolve competition with other writers.
+	if !rw.w.TryLock() {
+		if RaceEnabled {
+			RaceEnable()
+		}
+		return false
+	}
+	// Only proceed if there are no readers.
+	if !atomic.CompareAndSwapInt32(&rw.readerCount, 0, -rwmutexMaxReaders) {
+		rw.w.Unlock()
+		if RaceEnabled {
+			RaceEnable()
+		}
+		return false
+	}
+	if RaceEnabled {
+		RaceEnable()
+		RaceAcquire(unsafe.Pointer(&rw.writerSem))
+	}
+	return true
+}
+
 // Lock locks rw for writing.
 func (rw *DowngradableRWMutex) Lock() {
 	if RaceEnabled {
-- 
cgit v1.2.3


From 6a59e7f510a7b12f8b3bd768dfe569033ef07d30 Mon Sep 17 00:00:00 2001
From: Ian Gudger <igudger@google.com>
Date: Tue, 21 Jan 2020 19:23:26 -0800
Subject: Rename DowngradableRWMutex to RWmutex.

Also renames TMutex to Mutex.

These custom mutexes aren't any worse than the standard library versions (same
code), so having both seems redundant.

PiperOrigin-RevId: 290873587
---
 pkg/sentry/fs/overlay.go                |  2 +-
 pkg/sentry/mm/mm.go                     |  4 +--
 pkg/sync/aliases.go                     |  6 ----
 pkg/sync/downgradable_rwmutex_test.go   | 50 ++++++++++++++++-----------------
 pkg/sync/downgradable_rwmutex_unsafe.go | 26 ++++++++---------
 pkg/sync/tmutex_test.go                 |  8 +++---
 pkg/sync/tmutex_unsafe.go               |  8 +++---
 7 files changed, 49 insertions(+), 55 deletions(-)

(limited to 'pkg/sync')

diff --git a/pkg/sentry/fs/overlay.go b/pkg/sentry/fs/overlay.go
index 4cad55327..f7702f8f4 100644
--- a/pkg/sentry/fs/overlay.go
+++ b/pkg/sentry/fs/overlay.go
@@ -198,7 +198,7 @@ type overlayEntry struct {
 	upper *Inode
 
 	// dirCacheMu protects dirCache.
-	dirCacheMu sync.DowngradableRWMutex `state:"nosave"`
+	dirCacheMu sync.RWMutex `state:"nosave"`
 
 	// dirCache is cache of DentAttrs from upper and lower Inodes.
 	dirCache *SortedDentryMap
diff --git a/pkg/sentry/mm/mm.go b/pkg/sentry/mm/mm.go
index fa86ebced..78cc9e6e4 100644
--- a/pkg/sentry/mm/mm.go
+++ b/pkg/sentry/mm/mm.go
@@ -80,7 +80,7 @@ type MemoryManager struct {
 	users int32
 
 	// mappingMu is analogous to Linux's struct mm_struct::mmap_sem.
-	mappingMu sync.DowngradableRWMutex `state:"nosave"`
+	mappingMu sync.RWMutex `state:"nosave"`
 
 	// vmas stores virtual memory areas. Since vmas are stored by value,
 	// clients should usually use vmaIterator.ValuePtr() instead of
@@ -123,7 +123,7 @@ type MemoryManager struct {
 
 	// activeMu is loosely analogous to Linux's struct
 	// mm_struct::page_table_lock.
-	activeMu sync.DowngradableRWMutex `state:"nosave"`
+	activeMu sync.RWMutex `state:"nosave"`
 
 	// pmas stores platform mapping areas used to implement vmas. Since pmas
 	// are stored by value, clients should usually use pmaIterator.ValuePtr()
diff --git a/pkg/sync/aliases.go b/pkg/sync/aliases.go
index 20c7ca041..d2d7132fa 100644
--- a/pkg/sync/aliases.go
+++ b/pkg/sync/aliases.go
@@ -11,12 +11,6 @@ import (
 
 // Aliases of standard library types.
 type (
-	// Mutex is an alias of sync.Mutex.
-	Mutex = sync.Mutex
-
-	// RWMutex is an alias of sync.RWMutex.
-	RWMutex = sync.RWMutex
-
 	// Cond is an alias of sync.Cond.
 	Cond = sync.Cond
 
diff --git a/pkg/sync/downgradable_rwmutex_test.go b/pkg/sync/downgradable_rwmutex_test.go
index b5cb28ec0..ce667e825 100644
--- a/pkg/sync/downgradable_rwmutex_test.go
+++ b/pkg/sync/downgradable_rwmutex_test.go
@@ -18,7 +18,7 @@ import (
 	"testing"
 )
 
-func parallelReader(m *DowngradableRWMutex, clocked, cunlock, cdone chan bool) {
+func parallelReader(m *RWMutex, clocked, cunlock, cdone chan bool) {
 	m.RLock()
 	clocked <- true
 	<-cunlock
@@ -28,7 +28,7 @@ func parallelReader(m *DowngradableRWMutex, clocked, cunlock, cdone chan bool) {
 
 func doTestParallelReaders(numReaders, gomaxprocs int) {
 	runtime.GOMAXPROCS(gomaxprocs)
-	var m DowngradableRWMutex
+	var m RWMutex
 	clocked := make(chan bool)
 	cunlock := make(chan bool)
 	cdone := make(chan bool)
@@ -55,7 +55,7 @@ func TestParallelReaders(t *testing.T) {
 	doTestParallelReaders(4, 2)
 }
 
-func reader(rwm *DowngradableRWMutex, numIterations int, activity *int32, cdone chan bool) {
+func reader(rwm *RWMutex, numIterations int, activity *int32, cdone chan bool) {
 	for i := 0; i < numIterations; i++ {
 		rwm.RLock()
 		n := atomic.AddInt32(activity, 1)
@@ -70,7 +70,7 @@ func reader(rwm *DowngradableRWMutex, numIterations int, activity *int32, cdone
 	cdone <- true
 }
 
-func writer(rwm *DowngradableRWMutex, numIterations int, activity *int32, cdone chan bool) {
+func writer(rwm *RWMutex, numIterations int, activity *int32, cdone chan bool) {
 	for i := 0; i < numIterations; i++ {
 		rwm.Lock()
 		n := atomic.AddInt32(activity, 10000)
@@ -85,7 +85,7 @@ func writer(rwm *DowngradableRWMutex, numIterations int, activity *int32, cdone
 	cdone <- true
 }
 
-func downgradingWriter(rwm *DowngradableRWMutex, numIterations int, activity *int32, cdone chan bool) {
+func downgradingWriter(rwm *RWMutex, numIterations int, activity *int32, cdone chan bool) {
 	for i := 0; i < numIterations; i++ {
 		rwm.Lock()
 		n := atomic.AddInt32(activity, 10000)
@@ -112,7 +112,7 @@ func HammerDowngradableRWMutex(gomaxprocs, numReaders, numIterations int) {
 	runtime.GOMAXPROCS(gomaxprocs)
 	// Number of active readers + 10000 * number of active writers.
 	var activity int32
-	var rwm DowngradableRWMutex
+	var rwm RWMutex
 	cdone := make(chan bool)
 	go writer(&rwm, numIterations, &activity, cdone)
 	go downgradingWriter(&rwm, numIterations, &activity, cdone)
@@ -150,56 +150,56 @@ func TestDowngradableRWMutex(t *testing.T) {
 }
 
 func TestRWDoubleTryLock(t *testing.T) {
-	var m DowngradableRWMutex
-	if !m.TryLock() {
+	var rwm RWMutex
+	if !rwm.TryLock() {
 		t.Fatal("failed to aquire lock")
 	}
-	if m.TryLock() {
+	if rwm.TryLock() {
 		t.Fatal("unexpectedly succeeded in aquiring locked mutex")
 	}
 }
 
 func TestRWTryLockAfterLock(t *testing.T) {
-	var m DowngradableRWMutex
-	m.Lock()
-	if m.TryLock() {
+	var rwm RWMutex
+	rwm.Lock()
+	if rwm.TryLock() {
 		t.Fatal("unexpectedly succeeded in aquiring locked mutex")
 	}
 }
 
 func TestRWTryLockUnlock(t *testing.T) {
-	var m DowngradableRWMutex
-	if !m.TryLock() {
+	var rwm RWMutex
+	if !rwm.TryLock() {
 		t.Fatal("failed to aquire lock")
 	}
-	m.Unlock()
-	if !m.TryLock() {
+	rwm.Unlock()
+	if !rwm.TryLock() {
 		t.Fatal("failed to aquire lock after unlock")
 	}
 }
 
 func TestTryRLockAfterLock(t *testing.T) {
-	var m DowngradableRWMutex
-	m.Lock()
-	if m.TryRLock() {
+	var rwm RWMutex
+	rwm.Lock()
+	if rwm.TryRLock() {
 		t.Fatal("unexpectedly succeeded in aquiring locked mutex")
 	}
 }
 
 func TestTryLockAfterRLock(t *testing.T) {
-	var m DowngradableRWMutex
-	m.RLock()
-	if m.TryLock() {
+	var rwm RWMutex
+	rwm.RLock()
+	if rwm.TryLock() {
 		t.Fatal("unexpectedly succeeded in aquiring locked mutex")
 	}
 }
 
 func TestDoubleTryRLock(t *testing.T) {
-	var m DowngradableRWMutex
-	if !m.TryRLock() {
+	var rwm RWMutex
+	if !rwm.TryRLock() {
 		t.Fatal("failed to aquire lock")
 	}
-	if !m.TryRLock() {
+	if !rwm.TryRLock() {
 		t.Fatal("failed to read aquire read locked lock")
 	}
 }
diff --git a/pkg/sync/downgradable_rwmutex_unsafe.go b/pkg/sync/downgradable_rwmutex_unsafe.go
index 0d321f5e3..ea6cdc447 100644
--- a/pkg/sync/downgradable_rwmutex_unsafe.go
+++ b/pkg/sync/downgradable_rwmutex_unsafe.go
@@ -29,10 +29,10 @@ func runtimeSemacquire(s *uint32)
 //go:linkname runtimeSemrelease sync.runtime_Semrelease
 func runtimeSemrelease(s *uint32, handoff bool, skipframes int)
 
-// DowngradableRWMutex is identical to sync.RWMutex, but adds the DowngradeLock,
+// RWMutex is identical to sync.RWMutex, but adds the DowngradeLock,
 // TryLock and TryRLock methods.
-type DowngradableRWMutex struct {
-	w           TMutex // held if there are pending writers
+type RWMutex struct {
+	w           Mutex  // held if there are pending writers
 	writerSem   uint32 // semaphore for writers to wait for completing readers
 	readerSem   uint32 // semaphore for readers to wait for completing writers
 	readerCount int32  // number of pending readers
@@ -43,7 +43,7 @@ const rwmutexMaxReaders = 1 << 30
 
 // TryRLock locks rw for reading. It returns true if it succeeds and false
 // otherwise. It does not block.
-func (rw *DowngradableRWMutex) TryRLock() bool {
+func (rw *RWMutex) TryRLock() bool {
 	if RaceEnabled {
 		RaceDisable()
 	}
@@ -67,7 +67,7 @@ func (rw *DowngradableRWMutex) TryRLock() bool {
 }
 
 // RLock locks rw for reading.
-func (rw *DowngradableRWMutex) RLock() {
+func (rw *RWMutex) RLock() {
 	if RaceEnabled {
 		RaceDisable()
 	}
@@ -82,14 +82,14 @@ func (rw *DowngradableRWMutex) RLock() {
 }
 
 // RUnlock undoes a single RLock call.
-func (rw *DowngradableRWMutex) RUnlock() {
+func (rw *RWMutex) RUnlock() {
 	if RaceEnabled {
 		RaceReleaseMerge(unsafe.Pointer(&rw.writerSem))
 		RaceDisable()
 	}
 	if r := atomic.AddInt32(&rw.readerCount, -1); r < 0 {
 		if r+1 == 0 || r+1 == -rwmutexMaxReaders {
-			panic("RUnlock of unlocked DowngradableRWMutex")
+			panic("RUnlock of unlocked RWMutex")
 		}
 		// A writer is pending.
 		if atomic.AddInt32(&rw.readerWait, -1) == 0 {
@@ -104,7 +104,7 @@ func (rw *DowngradableRWMutex) RUnlock() {
 
 // TryLock locks rw for writing. It returns true if it succeeds and false
 // otherwise. It does not block.
-func (rw *DowngradableRWMutex) TryLock() bool {
+func (rw *RWMutex) TryLock() bool {
 	if RaceEnabled {
 		RaceDisable()
 	}
@@ -131,7 +131,7 @@ func (rw *DowngradableRWMutex) TryLock() bool {
 }
 
 // Lock locks rw for writing.
-func (rw *DowngradableRWMutex) Lock() {
+func (rw *RWMutex) Lock() {
 	if RaceEnabled {
 		RaceDisable()
 	}
@@ -150,7 +150,7 @@ func (rw *DowngradableRWMutex) Lock() {
 }
 
 // Unlock unlocks rw for writing.
-func (rw *DowngradableRWMutex) Unlock() {
+func (rw *RWMutex) Unlock() {
 	if RaceEnabled {
 		RaceRelease(unsafe.Pointer(&rw.writerSem))
 		RaceRelease(unsafe.Pointer(&rw.readerSem))
@@ -159,7 +159,7 @@ func (rw *DowngradableRWMutex) Unlock() {
 	// Announce to readers there is no active writer.
 	r := atomic.AddInt32(&rw.readerCount, rwmutexMaxReaders)
 	if r >= rwmutexMaxReaders {
-		panic("Unlock of unlocked DowngradableRWMutex")
+		panic("Unlock of unlocked RWMutex")
 	}
 	// Unblock blocked readers, if any.
 	for i := 0; i < int(r); i++ {
@@ -173,7 +173,7 @@ func (rw *DowngradableRWMutex) Unlock() {
 }
 
 // DowngradeLock atomically unlocks rw for writing and locks it for reading.
-func (rw *DowngradableRWMutex) DowngradeLock() {
+func (rw *RWMutex) DowngradeLock() {
 	if RaceEnabled {
 		RaceRelease(unsafe.Pointer(&rw.readerSem))
 		RaceDisable()
@@ -181,7 +181,7 @@ func (rw *DowngradableRWMutex) DowngradeLock() {
 	// Announce to readers there is no active writer and one additional reader.
 	r := atomic.AddInt32(&rw.readerCount, rwmutexMaxReaders+1)
 	if r >= rwmutexMaxReaders+1 {
-		panic("DowngradeLock of unlocked DowngradableRWMutex")
+		panic("DowngradeLock of unlocked RWMutex")
 	}
 	// Unblock blocked readers, if any. Note that this loop starts as 1 since r
 	// includes this goroutine.
diff --git a/pkg/sync/tmutex_test.go b/pkg/sync/tmutex_test.go
index c640bae23..0838248b4 100644
--- a/pkg/sync/tmutex_test.go
+++ b/pkg/sync/tmutex_test.go
@@ -30,7 +30,7 @@ func TestStructSize(t *testing.T) {
 //
 // The correctness of this package relies on these remaining in sync.
 func TestFieldValues(t *testing.T) {
-	var m TMutex
+	var m Mutex
 	m.Lock()
 	if got := *m.state(); got != mutexLocked {
 		t.Errorf("got locked sync.Mutex.state = %d, want = %d", got, mutexLocked)
@@ -42,7 +42,7 @@ func TestFieldValues(t *testing.T) {
 }
 
 func TestDoubleTryLock(t *testing.T) {
-	var m TMutex
+	var m Mutex
 	if !m.TryLock() {
 		t.Fatal("failed to aquire lock")
 	}
@@ -52,7 +52,7 @@ func TestDoubleTryLock(t *testing.T) {
 }
 
 func TestTryLockAfterLock(t *testing.T) {
-	var m TMutex
+	var m Mutex
 	m.Lock()
 	if m.TryLock() {
 		t.Fatal("unexpectedly succeeded in aquiring locked mutex")
@@ -60,7 +60,7 @@ func TestTryLockAfterLock(t *testing.T) {
 }
 
 func TestTryLockUnlock(t *testing.T) {
-	var m TMutex
+	var m Mutex
 	if !m.TryLock() {
 		t.Fatal("failed to aquire lock")
 	}
diff --git a/pkg/sync/tmutex_unsafe.go b/pkg/sync/tmutex_unsafe.go
index 3c32f8371..3dd15578b 100644
--- a/pkg/sync/tmutex_unsafe.go
+++ b/pkg/sync/tmutex_unsafe.go
@@ -17,8 +17,8 @@ import (
 	"unsafe"
 )
 
-// TMutex is a try lock.
-type TMutex struct {
+// Mutex is a try lock.
+type Mutex struct {
 	sync.Mutex
 }
 
@@ -27,7 +27,7 @@ type syncMutex struct {
 	sema  uint32
 }
 
-func (m *TMutex) state() *int32 {
+func (m *Mutex) state() *int32 {
 	return &(*syncMutex)(unsafe.Pointer(&m.Mutex)).state
 }
 
@@ -38,7 +38,7 @@ const (
 
 // TryLock tries to aquire the mutex. It returns true if it succeeds and false
 // otherwise. TryLock does not block.
-func (m *TMutex) TryLock() bool {
+func (m *Mutex) TryLock() bool {
 	if atomic.CompareAndSwapInt32(m.state(), mutexUnlocked, mutexLocked) {
 		if RaceEnabled {
 			RaceAcquire(unsafe.Pointer(&m.Mutex))
-- 
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