syncs: add Mutex/RWMutex alias/wrappers for future mutex debugging

Updates #17852

Change-Id: I477340fb8e40686870e981ade11cd61597c34a20
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

util/syspolicy/rsop/change_callbacks.go

@@ -9,6 +9,7 @@ import (
 	"sync"
 	"time"
 
+	"tailscale.com/syncs"
 	"tailscale.com/util/set"
 	"tailscale.com/util/syspolicy/internal/loggerx"
 	"tailscale.com/util/syspolicy/pkey"
@@ -70,7 +71,7 @@ func (c PolicyChange) HasChangedAnyOf(keys ...pkey.Key) bool {
 // policyChangeCallbacks are the callbacks to invoke when the effective policy changes.
 // It is safe for concurrent use.
 type policyChangeCallbacks struct {
-	mu  sync.Mutex
+	mu  syncs.Mutex
 	cbs set.HandleSet[PolicyChangeCallback]
 }
 

util/syspolicy/rsop/resultant_policy.go

@@ -7,10 +7,10 @@ import (
 	"errors"
 	"fmt"
 	"slices"
-	"sync"
 	"sync/atomic"
 	"time"
 
+	"tailscale.com/syncs"
 	"tailscale.com/util/syspolicy/internal/loggerx"
 	"tailscale.com/util/syspolicy/setting"
 	"tailscale.com/util/testenv"
@@ -58,7 +58,7 @@ type Policy struct {
 
 	changeCallbacks policyChangeCallbacks
 
-	mu             sync.Mutex
+	mu             syncs.Mutex
 	watcherStarted bool // whether [Policy.watchReload] was started
 	sources        source.ReadableSources
 	closing        bool // whether [Policy.Close] was called (even if we're still closing)

util/syspolicy/rsop/rsop.go

@@ -10,7 +10,6 @@ import (
 	"errors"
 	"fmt"
 	"slices"
-	"sync"
 
 	"tailscale.com/syncs"
 	"tailscale.com/util/slicesx"
@@ -20,7 +19,7 @@ import (
 )
 
 var (
-	policyMu          sync.Mutex       // protects [policySources] and [effectivePolicies]
+	policyMu          syncs.Mutex      // protects [policySources] and [effectivePolicies]
 	policySources     []*source.Source // all registered policy sources
 	effectivePolicies []*Policy        // all active (non-closed) effective policies returned by [PolicyFor]
 

util/syspolicy/setting/setting.go

@@ -11,9 +11,9 @@ import (
 	"fmt"
 	"slices"
 	"strings"
-	"sync"
 	"time"
 
+	"tailscale.com/syncs"
 	"tailscale.com/types/lazy"
 	"tailscale.com/util/syspolicy/internal"
 	"tailscale.com/util/syspolicy/pkey"
@@ -215,7 +215,7 @@ type DefinitionMap map[pkey.Key]*Definition
 var (
 	definitions lazy.SyncValue[DefinitionMap]
 
-	definitionsMu   sync.Mutex
+	definitionsMu   syncs.Mutex
 	definitionsList []*Definition
 	definitionsUsed bool
 )