Require sync.Mutex to lock and unlock from the same goroutine

We would like to track locks ordering to detect ordering violations. Detecting
violations is much simpler if mutexes must be unlocked by the same goroutine
that locked them.

Thus, as a first step to tracking lock ordering, add this lock/unlock
requirement to gVisor's sync.Mutex. This is more strict than the Go standard
library's sync.Mutex, but initial testing indicates only a single lock that is
used across goroutines. The new sync.CrossGoroutineMutex relaxes the
requirement (but will not provide lock order checking).

Due to the additional overhead, enforcement is only enabled with the
"checklocks" build tag. Build with this tag using:

bazel build --define=gotags=checklocks ...

From my spot-checking, this has no changed inlining properties when disabled.

Updates #4804

PiperOrigin-RevId: 343370200

1 files changed, 6 insertions, 1 deletions

diff --git a/pkg/sync/rwmutex_unsafe.go b/pkg/sync/rwmutex_unsafe.go
index b3b4dee78..fa023f5bb 100644
--- a/pkg/sync/rwmutex_unsafe.go
+++ b/pkg/sync/rwmutex_unsafe.go
@@ -32,7 +32,12 @@ 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
+	// w is held if there are pending writers
+	//
+	// We use CrossGoroutineMutex rather than Mutex because the lock
+	// annotation instrumentation in Mutex will trigger false positives in
+	// the race detector when called inside of RaceDisable.
+	w           CrossGoroutineMutex
 	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