From 40d81cf061d8a2a277d70446f582a984c1701ff3 Mon Sep 17 00:00:00 2001 From: Russ Cox Date: Tue, 18 Oct 2016 10:26:07 -0400 Subject: [PATCH] sync: throw, not panic, for unlock of unlocked mutex The panic leaves the lock in an unusable state. Trying to panic with a usable state makes the lock significantly less efficient and scalable (see early CL patch sets and discussion). Instead, use runtime.throw, which will crash the program directly. In general throw is reserved for when the runtime detects truly serious, unrecoverable problems. This problem is certainly serious, and, without a significant performance hit, is unrecoverable. Fixes #13879. Change-Id: I41920d9e2317270c6f909957d195bd8b68177f8d Reviewed-on: https://go-review.googlesource.com/31359 Reviewed-by: Austin Clements Reviewed-by: Brad Fitzpatrick --- src/runtime/panic.go | 5 ++ src/sync/mutex.go | 6 ++- src/sync/mutex_test.go | 106 +++++++++++++++++++++++++++++++++++---- src/sync/rwmutex.go | 4 +- src/sync/rwmutex_test.go | 42 ---------------- 5 files changed, 107 insertions(+), 56 deletions(-) diff --git a/src/runtime/panic.go b/src/runtime/panic.go index 9e108cc437..f78e67f9bb 100644 --- a/src/runtime/panic.go +++ b/src/runtime/panic.go @@ -576,6 +576,11 @@ func dopanic(unused int) { *(*int)(nil) = 0 } +//go:linkname sync_throw sync.throw +func sync_throw(s string) { + throw(s) +} + //go:nosplit func throw(s string) { print("fatal error: ", s, "\n") diff --git a/src/sync/mutex.go b/src/sync/mutex.go index 90892793f0..717934344e 100644 --- a/src/sync/mutex.go +++ b/src/sync/mutex.go @@ -16,6 +16,8 @@ import ( "unsafe" ) +func throw(string) // provided by runtime + // A Mutex is a mutual exclusion lock. // Mutexes can be created as part of other structures; // the zero value for a Mutex is an unlocked mutex. @@ -74,7 +76,7 @@ func (m *Mutex) Lock() { // The goroutine has been woken from sleep, // so we need to reset the flag in either case. if new&mutexWoken == 0 { - panic("sync: inconsistent mutex state") + throw("sync: inconsistent mutex state") } new &^= mutexWoken } @@ -108,7 +110,7 @@ func (m *Mutex) Unlock() { // Fast path: drop lock bit. new := atomic.AddInt32(&m.state, -mutexLocked) if (new+mutexLocked)&mutexLocked == 0 { - panic("sync: unlock of unlocked mutex") + throw("sync: unlock of unlocked mutex") } old := new diff --git a/src/sync/mutex_test.go b/src/sync/mutex_test.go index 91a4855cb1..fbfe4b77fe 100644 --- a/src/sync/mutex_test.go +++ b/src/sync/mutex_test.go @@ -7,7 +7,12 @@ package sync_test import ( + "fmt" + "internal/testenv" + "os" + "os/exec" "runtime" + "strings" . "sync" "testing" ) @@ -71,17 +76,98 @@ func TestMutex(t *testing.T) { } } -func TestMutexPanic(t *testing.T) { - defer func() { - if recover() == nil { - t.Fatalf("unlock of unlocked mutex did not panic") - } - }() +var misuseTests = []struct { + name string + f func() +}{ + { + "Mutex.Unlock", + func() { + var mu Mutex + mu.Unlock() + }, + }, + { + "Mutex.Unlock2", + func() { + var mu Mutex + mu.Lock() + mu.Unlock() + mu.Unlock() + }, + }, + { + "RWMutex.Unlock", + func() { + var mu RWMutex + mu.Unlock() + }, + }, + { + "RWMutex.Unlock2", + func() { + var mu RWMutex + mu.RLock() + mu.Unlock() + }, + }, + { + "RWMutex.Unlock3", + func() { + var mu RWMutex + mu.Lock() + mu.Unlock() + mu.Unlock() + }, + }, + { + "RWMutex.RUnlock", + func() { + var mu RWMutex + mu.RUnlock() + }, + }, + { + "RWMutex.RUnlock2", + func() { + var mu RWMutex + mu.Lock() + mu.RUnlock() + }, + }, + { + "RWMutex.RUnlock3", + func() { + var mu RWMutex + mu.RLock() + mu.RUnlock() + mu.RUnlock() + }, + }, +} - var mu Mutex - mu.Lock() - mu.Unlock() - mu.Unlock() +func init() { + if len(os.Args) == 3 && os.Args[1] == "TESTMISUSE" { + for _, test := range misuseTests { + if test.name == os.Args[2] { + test.f() + fmt.Printf("test completed\n") + os.Exit(0) + } + } + fmt.Printf("unknown test\n") + os.Exit(0) + } +} + +func TestMutexMisuse(t *testing.T) { + testenv.MustHaveExec(t) + for _, test := range misuseTests { + out, err := exec.Command(os.Args[0], "TESTMISUSE", test.name).CombinedOutput() + if err == nil || !strings.Contains(string(out), "unlocked") { + t.Errorf("%s: did not find failure with message about unlocked lock: %s\n%s\n", test.name, err, out) + } + } } func BenchmarkMutexUncontended(b *testing.B) { diff --git a/src/sync/rwmutex.go b/src/sync/rwmutex.go index 6734360e37..71064eeeba 100644 --- a/src/sync/rwmutex.go +++ b/src/sync/rwmutex.go @@ -61,7 +61,7 @@ func (rw *RWMutex) RUnlock() { if r := atomic.AddInt32(&rw.readerCount, -1); r < 0 { if r+1 == 0 || r+1 == -rwmutexMaxReaders { race.Enable() - panic("sync: RUnlock of unlocked RWMutex") + throw("sync: RUnlock of unlocked RWMutex") } // A writer is pending. if atomic.AddInt32(&rw.readerWait, -1) == 0 { @@ -115,7 +115,7 @@ func (rw *RWMutex) Unlock() { r := atomic.AddInt32(&rw.readerCount, rwmutexMaxReaders) if r >= rwmutexMaxReaders { race.Enable() - panic("sync: Unlock of unlocked RWMutex") + throw("sync: Unlock of unlocked RWMutex") } // Unblock blocked readers, if any. for i := 0; i < int(r); i++ { diff --git a/src/sync/rwmutex_test.go b/src/sync/rwmutex_test.go index f625bc3a58..0436f97239 100644 --- a/src/sync/rwmutex_test.go +++ b/src/sync/rwmutex_test.go @@ -155,48 +155,6 @@ func TestRLocker(t *testing.T) { } } -func TestUnlockPanic(t *testing.T) { - defer func() { - if recover() == nil { - t.Fatalf("unlock of unlocked RWMutex did not panic") - } - }() - var mu RWMutex - mu.Unlock() -} - -func TestUnlockPanic2(t *testing.T) { - defer func() { - if recover() == nil { - t.Fatalf("unlock of unlocked RWMutex did not panic") - } - }() - var mu RWMutex - mu.RLock() - mu.Unlock() -} - -func TestRUnlockPanic(t *testing.T) { - defer func() { - if recover() == nil { - t.Fatalf("read unlock of unlocked RWMutex did not panic") - } - }() - var mu RWMutex - mu.RUnlock() -} - -func TestRUnlockPanic2(t *testing.T) { - defer func() { - if recover() == nil { - t.Fatalf("read unlock of unlocked RWMutex did not panic") - } - }() - var mu RWMutex - mu.Lock() - mu.RUnlock() -} - func BenchmarkRWMutexUncontended(b *testing.B) { type PaddedRWMutex struct { RWMutex