diff --git a/doc/godebug.md b/doc/godebug.md
index 23427c85b5793c00eefecb851e2efb46cbb21301..1d6e6d78d07759e41278fec0d0650d6b72d93037 100644
--- a/doc/godebug.md
+++ b/doc/godebug.md
@@ -169,6 +169,9 @@ Go command will follow symlinks to regular files embedding files.
The default value `embedfollowsymlinks=0` does not allow following
symlinks. `embedfollowsymlinks=1` will allow following symlinks.
+Go 1.25 corrected the semantics of contention reports for runtime-internal locks,
+and so removed the [`runtimecontentionstacks` setting](/pkg/runtime#hdr-Environment_Variable).
+
### Go 1.24
Go 1.24 added a new `fips140` setting that controls whether the Go
diff --git a/doc/next/6-stdlib/99-minor/runtime/pprof/66999.md b/doc/next/6-stdlib/99-minor/runtime/pprof/66999.md
new file mode 100644
index 0000000000000000000000000000000000000000..f222628aae7f4a840cff0ff1ea24ddb8a58f0cce
--- /dev/null
+++ b/doc/next/6-stdlib/99-minor/runtime/pprof/66999.md
@@ -0,0 +1,6 @@
+The mutex profile for contention on runtime-internal locks now correctly points
+to the end of the critical section that caused the delay. This matches the
+profile's behavior for contention on `sync.Mutex` values. The
+`runtimecontentionstacks` setting for `GODEBUG`, which allowed opting in to the
+unusual behavior of Go 1.22 through 1.24 for this part of the profile, is now
+gone.
diff --git a/src/runtime/extern.go b/src/runtime/extern.go
index 8ee89ab94fd1cb974d0c5e5f93336e0720aa240f..eb30b0566ecb3661e8f7e5d1237f9dfd467182e0 100644
--- a/src/runtime/extern.go
+++ b/src/runtime/extern.go
@@ -166,15 +166,6 @@ It is a comma-separated list of name=val pairs setting these named variables:
panicnil: setting panicnil=1 disables the runtime error when calling panic with nil
interface value or an untyped nil.
- runtimecontentionstacks: setting runtimecontentionstacks=1 enables inclusion of call stacks
- related to contention on runtime-internal locks in the "mutex" profile, subject to the
- MutexProfileFraction setting. When runtimecontentionstacks=0, contention on
- runtime-internal locks will report as "runtime._LostContendedRuntimeLock". When
- runtimecontentionstacks=1, the call stacks will correspond to the unlock call that released
- the lock. But instead of the value corresponding to the amount of contention that call
- stack caused, it corresponds to the amount of time the caller of unlock had to wait in its
- original call to lock. A future release is expected to align those and remove this setting.
-
invalidptr: invalidptr=1 (the default) causes the garbage collector and stack
copier to crash the program if an invalid pointer value (for example, 1)
is found in a pointer-typed location. Setting invalidptr=0 disables this check.
diff --git a/src/runtime/metrics_test.go b/src/runtime/metrics_test.go
index 178dd968f72b56a50c6283ca967829060b13739d..5fc022efc6cf1d844b85be0b9162e3e3d8c5087e 100644
--- a/src/runtime/metrics_test.go
+++ b/src/runtime/metrics_test.go
@@ -6,7 +6,6 @@ package runtime_test
import (
"bytes"
- "fmt"
"internal/abi"
"internal/goexperiment"
"internal/profile"
@@ -955,17 +954,6 @@ func TestRuntimeLockMetricsAndProfile(t *testing.T) {
t.Fatalf("need MutexProfileRate 0, got %d", old)
}
- {
- before := os.Getenv("GODEBUG")
- for _, s := range strings.Split(before, ",") {
- if strings.HasPrefix(s, "runtimecontentionstacks=") {
- t.Logf("GODEBUG includes explicit setting %q", s)
- }
- }
- defer func() { os.Setenv("GODEBUG", before) }()
- os.Setenv("GODEBUG", fmt.Sprintf("%s,runtimecontentionstacks=1", before))
- }
-
t.Logf("NumCPU %d", runtime.NumCPU())
t.Logf("GOMAXPROCS %d", runtime.GOMAXPROCS(0))
if minCPU := 2; runtime.NumCPU() < minCPU {
@@ -1229,9 +1217,9 @@ func TestRuntimeLockMetricsAndProfile(t *testing.T) {
stks[i] = []string{
"runtime.unlock",
- "runtime_test." + name + ".func5.1.1",
+ "runtime_test." + name + ".func4.1.1",
marker,
- "runtime_test." + name + ".func5.1",
+ "runtime_test." + name + ".func4.1",
"runtime_test.(*contentionWorker).run",
}
}
@@ -1411,14 +1399,14 @@ func TestRuntimeLockMetricsAndProfile(t *testing.T) {
{
"runtime.unlock",
"runtime.semrelease1",
- "runtime_test.TestRuntimeLockMetricsAndProfile.func6.1",
+ "runtime_test.TestRuntimeLockMetricsAndProfile.func5.1",
"runtime_test.(*contentionWorker).run",
},
{
"runtime.unlock",
"runtime.semacquire1",
"runtime.semacquire",
- "runtime_test.TestRuntimeLockMetricsAndProfile.func6.1",
+ "runtime_test.TestRuntimeLockMetricsAndProfile.func5.1",
"runtime_test.(*contentionWorker).run",
},
}
diff --git a/src/runtime/mprof.go b/src/runtime/mprof.go
index f80c8418ac01fd372f52863be99dbce87cad6293..5e2643600dc040410591e4b3436492a38a887ada 100644
--- a/src/runtime/mprof.go
+++ b/src/runtime/mprof.go
@@ -732,11 +732,6 @@ func (prof *mLockProfile) captureStack() {
prof.haveStack = true
prof.stack[0] = logicalStackSentinel
- if debug.runtimeContentionStacks.Load() == 0 {
- prof.stack[1] = abi.FuncPCABIInternal(_LostContendedRuntimeLock) + sys.PCQuantum
- prof.stack[2] = 0
- return
- }
var nstk int
gp := getg()
diff --git a/src/runtime/pprof/pprof.go b/src/runtime/pprof/pprof.go
index b7680a13fdcb2589ed7a4be0fb03b26764c28c78..d295991ef7819358bc0559a71258863e7e90cac6 100644
--- a/src/runtime/pprof/pprof.go
+++ b/src/runtime/pprof/pprof.go
@@ -169,12 +169,6 @@ import (
// holds a lock for 1s while 5 other goroutines are waiting for the entire
// second to acquire the lock, its unlock call stack will report 5s of
// contention.
-//
-// Runtime-internal locks are always reported at the location
-// "runtime._LostContendedRuntimeLock". More detailed stack traces for
-// runtime-internal locks can be obtained by setting
-// `GODEBUG=runtimecontentionstacks=1` (see package [runtime] docs for
-// caveats).
type Profile struct {
name string
mu sync.Mutex
diff --git a/src/runtime/runtime1.go b/src/runtime/runtime1.go
index ec4f7d043393f42f853a89fef3b8b67794165d86..2132ceecb2f0869249572a2c95cfd77f1537bde0 100644
--- a/src/runtime/runtime1.go
+++ b/src/runtime/runtime1.go
@@ -320,7 +320,6 @@ var debug struct {
gctrace int32
invalidptr int32
madvdontneed int32 // for Linux; issue 28466
- runtimeContentionStacks atomic.Int32
scavtrace int32
scheddetail int32
schedtrace int32
@@ -385,7 +384,6 @@ var dbgvars = []*dbgVar{
{name: "madvdontneed", value: &debug.madvdontneed},
{name: "panicnil", atomic: &debug.panicnil},
{name: "profstackdepth", value: &debug.profstackdepth, def: 128},
- {name: "runtimecontentionstacks", atomic: &debug.runtimeContentionStacks},
{name: "sbrk", value: &debug.sbrk},
{name: "scavtrace", value: &debug.scavtrace},
{name: "scheddetail", value: &debug.scheddetail},