2 files changed, 47 insertions, 12 deletions
diff --git a/src/syscall/pwd_plan9.go b/src/syscall/pwd_plan9.go
index 1deeaa9061..28e99565ee 100644
--- a/src/syscall/pwd_plan9.go
+++ b/src/syscall/pwd_plan9.go
@@ -11,7 +11,10 @@
 
 package syscall
 
-import "sync"
+import (
+	"runtime"
+	"sync"
+)
 
 var (
 	wdmu  sync.Mutex // guards following
@@ -19,6 +22,12 @@ var (
 	wdStr string
 )
 
+// Ensure current working directory seen by this goroutine matches
+// the most recent Chdir called in any goroutine. It's called internally
+// before executing any syscall which uses a relative pathname. Must
+// be called with the goroutine locked to the OS thread, to prevent
+// rescheduling on a different thread (potentially with a different
+// working directory) before the syscall is executed.
 func Fixwd() {
 	wdmu.Lock()
 	defer wdmu.Unlock()
@@ -39,13 +48,17 @@ func fixwdLocked() {
 	}
 }
 
-func fixwd(paths ...string) {
+// If any of the paths is relative, call Fixwd and return true
+// (locked to OS thread). Otherwise return false.
+func fixwd(paths ...string) bool {
 	for _, path := range paths {
 		if path != "" && path[0] != '/' && path[0] != '#' {
+			runtime.LockOSThread()
 			Fixwd()
-			return
+			return true
 		}
 	}
+	return false
 }
 
 // goroutine-specific getwd
@@ -75,10 +88,15 @@ func Getwd() (wd string, err error) {
 }
 
 func Chdir(path string) error {
-	fixwd(path)
+	// If Chdir is to a relative path, sync working dir first
+	if fixwd(path) {
+		defer runtime.UnlockOSThread()
+	}
 	wdmu.Lock()
 	defer wdmu.Unlock()
 
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
 	if err := chdir(path); err != nil {
 		return err
 	}
diff --git a/src/syscall/syscall_plan9.go b/src/syscall/syscall_plan9.go
index ca286c8c97..92414709ef 100644
--- a/src/syscall/syscall_plan9.go
+++ b/src/syscall/syscall_plan9.go
@@ -13,6 +13,7 @@ package syscall
 
 import (
 	"internal/oserror"
+	"runtime"
 	"unsafe"
 )
 
@@ -301,7 +302,9 @@ func Await(w *Waitmsg) (err error) {
 }
 
 func Unmount(name, old string) (err error) {
-	fixwd(name, old)
+	if fixwd(name, old) {
+		defer runtime.UnlockOSThread()
+	}
 	oldp, err := BytePtrFromString(old)
 	if err != nil {
 		return err
@@ -384,49 +387,63 @@ func Getgroups() (gids []int, err error) {
 //sys	open(path string, mode int) (fd int, err error)
 
 func Open(path string, mode int) (fd int, err error) {
-	fixwd(path)
+	if fixwd(path) {
+		defer runtime.UnlockOSThread()
+	}
 	return open(path, mode)
 }
 
 //sys	create(path string, mode int, perm uint32) (fd int, err error)
 
 func Create(path string, mode int, perm uint32) (fd int, err error) {
-	fixwd(path)
+	if fixwd(path) {
+		defer runtime.UnlockOSThread()
+	}
 	return create(path, mode, perm)
 }
 
 //sys	remove(path string) (err error)
 
 func Remove(path string) error {
-	fixwd(path)
+	if fixwd(path) {
+		defer runtime.UnlockOSThread()
+	}
 	return remove(path)
 }
 
 //sys	stat(path string, edir []byte) (n int, err error)
 
 func Stat(path string, edir []byte) (n int, err error) {
-	fixwd(path)
+	if fixwd(path) {
+		defer runtime.UnlockOSThread()
+	}
 	return stat(path, edir)
 }
 
 //sys	bind(name string, old string, flag int) (err error)
 
 func Bind(name string, old string, flag int) (err error) {
-	fixwd(name, old)
+	if fixwd(name, old) {
+		defer runtime.UnlockOSThread()
+	}
 	return bind(name, old, flag)
 }
 
 //sys	mount(fd int, afd int, old string, flag int, aname string) (err error)
 
 func Mount(fd int, afd int, old string, flag int, aname string) (err error) {
-	fixwd(old)
+	if fixwd(old) {
+		defer runtime.UnlockOSThread()
+	}
 	return mount(fd, afd, old, flag, aname)
 }
 
 //sys	wstat(path string, edir []byte) (err error)
 
 func Wstat(path string, edir []byte) (err error) {
-	fixwd(path)
+	if fixwd(path) {
+		defer runtime.UnlockOSThread()
+	}
 	return wstat(path, edir)
 }