1 files changed, 198 insertions, 0 deletions
diff --git a/pkg/sync/rwmutex_unsafe.go b/pkg/sync/rwmutex_unsafe.go
new file mode 100755
index 000000000..ea6cdc447
--- /dev/null
+++ b/pkg/sync/rwmutex_unsafe.go
@@ -0,0 +1,198 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// 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
+
+// Check go:linkname function signatures when updating Go version.
+
+// This is mostly copied from the standard library's sync/rwmutex.go.
+//
+// Happens-before relationships indicated to the race detector:
+// - Unlock -> Lock (via writerSem)
+// - Unlock -> RLock (via readerSem)
+// - RUnlock -> Lock (via writerSem)
+// - DowngradeLock -> RLock (via readerSem)
+
+package sync
+
+import (
+	"sync/atomic"
+	"unsafe"
+)
+
+//go:linkname runtimeSemacquire sync.runtime_Semacquire
+func runtimeSemacquire(s *uint32)
+
+//go:linkname runtimeSemrelease sync.runtime_Semrelease
+func runtimeSemrelease(s *uint32, handoff bool, skipframes int)
+
+// RWMutex is identical to sync.RWMutex, but adds the DowngradeLock,
+// TryLock and TryRLock methods.
+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
+	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 *RWMutex) 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 *RWMutex) RLock() {
+	if RaceEnabled {
+		RaceDisable()
+	}
+	if atomic.AddInt32(&rw.readerCount, 1) < 0 {
+		// A writer is pending, wait for it.
+		runtimeSemacquire(&rw.readerSem)
+	}
+	if RaceEnabled {
+		RaceEnable()
+		RaceAcquire(unsafe.Pointer(&rw.readerSem))
+	}
+}
+
+// RUnlock undoes a single RLock call.
+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 RWMutex")
+		}
+		// A writer is pending.
+		if atomic.AddInt32(&rw.readerWait, -1) == 0 {
+			// The last reader unblocks the writer.
+			runtimeSemrelease(&rw.writerSem, false, 0)
+		}
+	}
+	if RaceEnabled {
+		RaceEnable()
+	}
+}
+
+// TryLock locks rw for writing. It returns true if it succeeds and false
+// otherwise. It does not block.
+func (rw *RWMutex) 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 *RWMutex) Lock() {
+	if RaceEnabled {
+		RaceDisable()
+	}
+	// First, resolve competition with other writers.
+	rw.w.Lock()
+	// Announce to readers there is a pending writer.
+	r := atomic.AddInt32(&rw.readerCount, -rwmutexMaxReaders) + rwmutexMaxReaders
+	// Wait for active readers.
+	if r != 0 && atomic.AddInt32(&rw.readerWait, r) != 0 {
+		runtimeSemacquire(&rw.writerSem)
+	}
+	if RaceEnabled {
+		RaceEnable()
+		RaceAcquire(unsafe.Pointer(&rw.writerSem))
+	}
+}
+
+// Unlock unlocks rw for writing.
+func (rw *RWMutex) Unlock() {
+	if RaceEnabled {
+		RaceRelease(unsafe.Pointer(&rw.writerSem))
+		RaceRelease(unsafe.Pointer(&rw.readerSem))
+		RaceDisable()
+	}
+	// Announce to readers there is no active writer.
+	r := atomic.AddInt32(&rw.readerCount, rwmutexMaxReaders)
+	if r >= rwmutexMaxReaders {
+		panic("Unlock of unlocked RWMutex")
+	}
+	// Unblock blocked readers, if any.
+	for i := 0; i < int(r); i++ {
+		runtimeSemrelease(&rw.readerSem, false, 0)
+	}
+	// Allow other writers to proceed.
+	rw.w.Unlock()
+	if RaceEnabled {
+		RaceEnable()
+	}
+}
+
+// DowngradeLock atomically unlocks rw for writing and locks it for reading.
+func (rw *RWMutex) DowngradeLock() {
+	if RaceEnabled {
+		RaceRelease(unsafe.Pointer(&rw.readerSem))
+		RaceDisable()
+	}
+	// 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 RWMutex")
+	}
+	// Unblock blocked readers, if any. Note that this loop starts as 1 since r
+	// includes this goroutine.
+	for i := 1; i < int(r); i++ {
+		runtimeSemrelease(&rw.readerSem, false, 0)
+	}
+	// Allow other writers to proceed to rw.w.Lock(). Note that they will still
+	// block on rw.writerSem since at least this reader exists, such that
+	// DowngradeLock() is atomic with the previous write lock.
+	rw.w.Unlock()
+	if RaceEnabled {
+		RaceEnable()
+	}
+}