os: make use of pidfd on linux
Use Process.handle field to store pidfd, and make use of it. Only use
pidfd functionality if all the needed syscalls are available.
1. Add/use pidfdWorks, which checks that all needed pidfd-related
functionality works.
2. os.StartProcess: obtain the pidfd from the kernel, if possible, using
the functionality added by CL 520266. Note we could not modify
syscall.StartProcess to return pidfd directly because it is a public
API and its callers do not expect it, so we have to use ensurePidfd
and getPidfd.
3. (*Process).Kill: use pidfdSendSignal, if available and the pidfd is
known. Otherwise, fall back to the old implementation.
4. (*Process).Wait: use pidfdWait, if available, otherwise fall back to
using waitid/wait4. This is more complicated than expected due to
struct siginfo_t idiosyncrasy.
NOTE pidfdSendSignal and pidfdWait are used without a race workaround
(blockUntilWaitable and sigMu, added by CL 23967) because with pidfd,
PID recycle issue doesn't exist (IOW, pidfd, unlike PID, is guaranteed
to refer to one particular process) and thus the race doesn't exist
either.
Rework of CL 528438 (reverted in CL 566477 because of #65857).
For #62654.
Updates #13987.
Change-Id: If5ef8920bd8619dc428b6282ffe4fb8c258ca224
Reviewed-on: https://go-review.googlesource.com/c/go/+/570036
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Kirill Kolyshkin <kolyshkin@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Cherry Mui <cherryyz@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
diff --git a/src/internal/syscall/unix/pidfd_linux.go b/src/internal/syscall/unix/pidfd_linux.go
index 02cfaa0..e941762 100644
--- a/src/internal/syscall/unix/pidfd_linux.go
+++ b/src/internal/syscall/unix/pidfd_linux.go
@@ -13,3 +13,11 @@
}
return nil
}
+
+func PidFDOpen(pid, flags int) (uintptr, error) {
+ pidfd, _, errno := syscall.Syscall(pidfdOpenTrap, uintptr(pid), uintptr(flags), 0)
+ if errno != 0 {
+ return ^uintptr(0), errno
+ }
+ return uintptr(pidfd), nil
+}
diff --git a/src/internal/syscall/unix/siginfo_linux.go b/src/internal/syscall/unix/siginfo_linux.go
new file mode 100644
index 0000000..9f83114
--- /dev/null
+++ b/src/internal/syscall/unix/siginfo_linux.go
@@ -0,0 +1,64 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package unix
+
+import (
+ "syscall"
+)
+
+const is64bit = ^uint(0) >> 63 // 0 for 32-bit hosts, 1 for 64-bit ones.
+
+// SiginfoChild is a struct filled in by Linux waitid syscall.
+// In C, siginfo_t contains a union with multiple members;
+// this struct corresponds to one used when Signo is SIGCHLD.
+//
+// NOTE fields are exported to be used by TestSiginfoChildLayout.
+type SiginfoChild struct {
+ Signo int32
+ siErrnoCode // Two int32 fields, swapped on MIPS.
+ _ [is64bit]int32 // Extra padding for 64-bit hosts only.
+
+ // End of common part. Beginning of signal-specific part.
+
+ Pid int32
+ Uid uint32
+ Status int32
+
+ // Pad to 128 bytes.
+ _ [128 - (6+is64bit)*4]byte
+}
+
+const (
+ // Possible values for SiginfoChild.Code field.
+ _CLD_EXITED int32 = 1
+ _CLD_KILLED = 2
+ _CLD_DUMPED = 3
+ _CLD_TRAPPED = 4
+ _CLD_STOPPED = 5
+ _CLD_CONTINUED = 6
+
+ // These are the same as in syscall/syscall_linux.go.
+ core = 0x80
+ stopped = 0x7f
+ continued = 0xffff
+)
+
+// WaitStatus converts SiginfoChild, as filled in by the waitid syscall,
+// to syscall.WaitStatus.
+func (s *SiginfoChild) WaitStatus() (ws syscall.WaitStatus) {
+ switch s.Code {
+ case _CLD_EXITED:
+ ws = syscall.WaitStatus(s.Status << 8)
+ case _CLD_DUMPED:
+ ws = syscall.WaitStatus(s.Status) | core
+ case _CLD_KILLED:
+ ws = syscall.WaitStatus(s.Status)
+ case _CLD_TRAPPED, _CLD_STOPPED:
+ ws = syscall.WaitStatus(s.Status<<8) | stopped
+ case _CLD_CONTINUED:
+ ws = continued
+ }
+ return
+}
diff --git a/src/internal/syscall/unix/siginfo_linux_mipsx.go b/src/internal/syscall/unix/siginfo_linux_mipsx.go
new file mode 100644
index 0000000..2fca0c5
--- /dev/null
+++ b/src/internal/syscall/unix/siginfo_linux_mipsx.go
@@ -0,0 +1,12 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build linux && (mips || mipsle || mips64 || mips64le)
+
+package unix
+
+type siErrnoCode struct {
+ Code int32
+ Errno int32
+}
diff --git a/src/internal/syscall/unix/siginfo_linux_other.go b/src/internal/syscall/unix/siginfo_linux_other.go
new file mode 100644
index 0000000..cfdc4dd
--- /dev/null
+++ b/src/internal/syscall/unix/siginfo_linux_other.go
@@ -0,0 +1,12 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build linux && !(mips || mipsle || mips64 || mips64le)
+
+package unix
+
+type siErrnoCode struct {
+ Errno int32
+ Code int32
+}
diff --git a/src/internal/syscall/unix/siginfo_linux_test.go b/src/internal/syscall/unix/siginfo_linux_test.go
new file mode 100644
index 0000000..596c2eb
--- /dev/null
+++ b/src/internal/syscall/unix/siginfo_linux_test.go
@@ -0,0 +1,59 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package unix_test
+
+import (
+ "internal/goarch"
+ "internal/syscall/unix"
+ "runtime"
+ "strings"
+ "testing"
+ "unsafe"
+)
+
+// TestSiginfoChildLayout validates SiginfoChild layout. Modelled after
+// static assertions in linux kernel's arch/*/kernel/signal*.c.
+func TestSiginfoChildLayout(t *testing.T) {
+ var si unix.SiginfoChild
+
+ const host64bit = goarch.PtrSize == 8
+
+ if v := unsafe.Sizeof(si); v != 128 {
+ t.Fatalf("sizeof: got %d, want 128", v)
+ }
+
+ ofSigno := 0
+ ofErrno := 4
+ ofCode := 8
+ if strings.HasPrefix(runtime.GOARCH, "mips") {
+ // These two fields are swapped on MIPS platforms.
+ ofErrno, ofCode = ofCode, ofErrno
+ }
+ ofPid := 12
+ if host64bit {
+ ofPid = 16
+ }
+ ofUid := ofPid + 4
+ ofStatus := ofPid + 8
+
+ offsets := []struct {
+ name string
+ got uintptr
+ want int
+ }{
+ {"Signo", unsafe.Offsetof(si.Signo), ofSigno},
+ {"Errno", unsafe.Offsetof(si.Errno), ofErrno},
+ {"Code", unsafe.Offsetof(si.Code), ofCode},
+ {"Pid", unsafe.Offsetof(si.Pid), ofPid},
+ {"Uid", unsafe.Offsetof(si.Uid), ofUid},
+ {"Status", unsafe.Offsetof(si.Status), ofStatus},
+ }
+
+ for _, tc := range offsets {
+ if int(tc.got) != tc.want {
+ t.Errorf("offsetof %s: got %d, want %d", tc.name, tc.got, tc.want)
+ }
+ }
+}
diff --git a/src/internal/syscall/unix/sysnum_linux_386.go b/src/internal/syscall/unix/sysnum_linux_386.go
index 9f750a1..be048bc 100644
--- a/src/internal/syscall/unix/sysnum_linux_386.go
+++ b/src/internal/syscall/unix/sysnum_linux_386.go
@@ -8,4 +8,5 @@
getrandomTrap uintptr = 355
copyFileRangeTrap uintptr = 377
pidfdSendSignalTrap uintptr = 424
+ pidfdOpenTrap uintptr = 434
)
diff --git a/src/internal/syscall/unix/sysnum_linux_amd64.go b/src/internal/syscall/unix/sysnum_linux_amd64.go
index 706898d..525de9c 100644
--- a/src/internal/syscall/unix/sysnum_linux_amd64.go
+++ b/src/internal/syscall/unix/sysnum_linux_amd64.go
@@ -8,4 +8,5 @@
getrandomTrap uintptr = 318
copyFileRangeTrap uintptr = 326
pidfdSendSignalTrap uintptr = 424
+ pidfdOpenTrap uintptr = 434
)
diff --git a/src/internal/syscall/unix/sysnum_linux_arm.go b/src/internal/syscall/unix/sysnum_linux_arm.go
index c00644b..b803892 100644
--- a/src/internal/syscall/unix/sysnum_linux_arm.go
+++ b/src/internal/syscall/unix/sysnum_linux_arm.go
@@ -8,4 +8,5 @@
getrandomTrap uintptr = 384
copyFileRangeTrap uintptr = 391
pidfdSendSignalTrap uintptr = 424
+ pidfdOpenTrap uintptr = 434
)
diff --git a/src/internal/syscall/unix/sysnum_linux_generic.go b/src/internal/syscall/unix/sysnum_linux_generic.go
index bf25428..b06bf69 100644
--- a/src/internal/syscall/unix/sysnum_linux_generic.go
+++ b/src/internal/syscall/unix/sysnum_linux_generic.go
@@ -14,4 +14,5 @@
getrandomTrap uintptr = 278
copyFileRangeTrap uintptr = 285
pidfdSendSignalTrap uintptr = 424
+ pidfdOpenTrap uintptr = 434
)
diff --git a/src/internal/syscall/unix/sysnum_linux_mips64x.go b/src/internal/syscall/unix/sysnum_linux_mips64x.go
index 6a9e238..8764f5d 100644
--- a/src/internal/syscall/unix/sysnum_linux_mips64x.go
+++ b/src/internal/syscall/unix/sysnum_linux_mips64x.go
@@ -10,4 +10,5 @@
getrandomTrap uintptr = 5313
copyFileRangeTrap uintptr = 5320
pidfdSendSignalTrap uintptr = 5424
+ pidfdOpenTrap uintptr = 5434
)
diff --git a/src/internal/syscall/unix/sysnum_linux_mipsx.go b/src/internal/syscall/unix/sysnum_linux_mipsx.go
index 22d38f1..9b2e587 100644
--- a/src/internal/syscall/unix/sysnum_linux_mipsx.go
+++ b/src/internal/syscall/unix/sysnum_linux_mipsx.go
@@ -10,4 +10,5 @@
getrandomTrap uintptr = 4353
copyFileRangeTrap uintptr = 4360
pidfdSendSignalTrap uintptr = 4424
+ pidfdOpenTrap uintptr = 4434
)
diff --git a/src/internal/syscall/unix/sysnum_linux_ppc64x.go b/src/internal/syscall/unix/sysnum_linux_ppc64x.go
index 945ec28..03e9c19 100644
--- a/src/internal/syscall/unix/sysnum_linux_ppc64x.go
+++ b/src/internal/syscall/unix/sysnum_linux_ppc64x.go
@@ -10,4 +10,5 @@
getrandomTrap uintptr = 359
copyFileRangeTrap uintptr = 379
pidfdSendSignalTrap uintptr = 424
+ pidfdOpenTrap uintptr = 434
)
diff --git a/src/internal/syscall/unix/sysnum_linux_s390x.go b/src/internal/syscall/unix/sysnum_linux_s390x.go
index 2c74343..c6e3e02 100644
--- a/src/internal/syscall/unix/sysnum_linux_s390x.go
+++ b/src/internal/syscall/unix/sysnum_linux_s390x.go
@@ -8,4 +8,5 @@
getrandomTrap uintptr = 349
copyFileRangeTrap uintptr = 375
pidfdSendSignalTrap uintptr = 424
+ pidfdOpenTrap uintptr = 434
)
diff --git a/src/os/exec.go b/src/os/exec.go
index 12ba293..7a66d06 100644
--- a/src/os/exec.go
+++ b/src/os/exec.go
@@ -20,9 +20,9 @@
// Process stores the information about a process created by [StartProcess].
type Process struct {
Pid int
- handle atomic.Uintptr
- isdone atomic.Bool // process has been successfully waited on
- sigMu sync.RWMutex // avoid race between wait and signal
+ handle atomic.Uintptr // Process handle for Windows, pidfd for Linux.
+ isdone atomic.Bool // process has been successfully waited on
+ sigMu sync.RWMutex // avoid race between wait and signal
}
func newProcess(pid int, handle uintptr) *Process {
diff --git a/src/os/exec_posix.go b/src/os/exec_posix.go
index 4f9ea08..74d4fe6 100644
--- a/src/os/exec_posix.go
+++ b/src/os/exec_posix.go
@@ -13,6 +13,10 @@
"syscall"
)
+// unsetHandle is a value for Process.handle used when the handle is not set.
+// Same as syscall.InvalidHandle for Windows.
+const unsetHandle = ^uintptr(0)
+
// The only signal values guaranteed to be present in the os package on all
// systems are os.Interrupt (send the process an interrupt) and os.Kill (force
// the process to exit). On Windows, sending os.Interrupt to a process with
@@ -38,7 +42,7 @@
sysattr := &syscall.ProcAttr{
Dir: attr.Dir,
Env: attr.Env,
- Sys: attr.Sys,
+ Sys: ensurePidfd(attr.Sys),
}
if sysattr.Env == nil {
sysattr.Env, err = execenv.Default(sysattr.Sys)
@@ -60,6 +64,11 @@
return nil, &PathError{Op: "fork/exec", Path: name, Err: e}
}
+ // For Windows, syscall.StartProcess above already returned a process handle.
+ if runtime.GOOS != "windows" {
+ h = getPidfd(sysattr.Sys)
+ }
+
return newProcess(pid, h), nil
}
diff --git a/src/os/exec_unix.go b/src/os/exec_unix.go
index 36b320d..9f5810ff 100644
--- a/src/os/exec_unix.go
+++ b/src/os/exec_unix.go
@@ -17,6 +17,15 @@
if p.Pid == -1 {
return nil, syscall.EINVAL
}
+ // Wait on pidfd if possible; fallback to using pid on ENOSYS.
+ //
+ // When pidfd is used, there is no wait/kill race (described in CL 23967)
+ // because PID recycle issue doesn't exist (IOW, pidfd, unlike PID, is
+ // guaranteed to refer to one particular process). Thus, there is no
+ // need for the workaround (blockUntilWaitable + sigMu) below.
+ if ps, e := p.pidfdWait(); e != syscall.ENOSYS {
+ return ps, NewSyscallError("waitid", e)
+ }
// If we can block until Wait4 will succeed immediately, do so.
ready, err := p.blockUntilWaitable()
@@ -64,26 +73,31 @@
if p.Pid == 0 {
return errors.New("os: process not initialized")
}
+ s, ok := sig.(syscall.Signal)
+ if !ok {
+ return errors.New("os: unsupported signal type")
+ }
+ // Use pidfd if possible; fallback on ENOSYS.
+ if err := p.pidfdSendSignal(s); err != syscall.ENOSYS {
+ return err
+ }
p.sigMu.RLock()
defer p.sigMu.RUnlock()
if p.done() {
return ErrProcessDone
}
- s, ok := sig.(syscall.Signal)
- if !ok {
- return errors.New("os: unsupported signal type")
+ return convertESRCH(syscall.Kill(p.Pid, s))
+}
+
+func convertESRCH(err error) error {
+ if err == syscall.ESRCH {
+ return ErrProcessDone
}
- if e := syscall.Kill(p.Pid, s); e != nil {
- if e == syscall.ESRCH {
- return ErrProcessDone
- }
- return e
- }
- return nil
+ return err
}
func (p *Process) release() error {
- // NOOP for unix.
+ p.pidfdRelease()
p.Pid = -1
// no need for a finalizer anymore
runtime.SetFinalizer(p, nil)
@@ -92,7 +106,7 @@
func findProcess(pid int) (p *Process, err error) {
// NOOP for unix.
- return newProcess(pid, 0), nil
+ return newProcess(pid, unsetHandle), nil
}
func (p *ProcessState) userTime() time.Duration {
diff --git a/src/os/export_linux_test.go b/src/os/export_linux_test.go
index 78c2d14..55f83c8 100644
--- a/src/os/export_linux_test.go
+++ b/src/os/export_linux_test.go
@@ -8,4 +8,5 @@
PollCopyFileRangeP = &pollCopyFileRange
PollSpliceFile = &pollSplice
GetPollFDAndNetwork = getPollFDAndNetwork
+ CheckPidfdOnce = checkPidfdOnce
)
diff --git a/src/os/pidfd_linux.go b/src/os/pidfd_linux.go
new file mode 100644
index 0000000..3701be5
--- /dev/null
+++ b/src/os/pidfd_linux.go
@@ -0,0 +1,143 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Support for pidfd was added during the course of a few Linux releases:
+// v5.1: pidfd_send_signal syscall;
+// v5.2: CLONE_PIDFD flag for clone syscall;
+// v5.3: pidfd_open syscall, clone3 syscall;
+// v5.4: P_PIDFD idtype support for waitid syscall;
+// v5.6: pidfd_getfd syscall.
+
+package os
+
+import (
+ "internal/syscall/unix"
+ "sync"
+ "syscall"
+ "unsafe"
+)
+
+func ensurePidfd(sysAttr *syscall.SysProcAttr) *syscall.SysProcAttr {
+ if !pidfdWorks() {
+ return sysAttr
+ }
+
+ var pidfd int
+
+ if sysAttr == nil {
+ return &syscall.SysProcAttr{
+ PidFD: &pidfd,
+ }
+ }
+ if sysAttr.PidFD == nil {
+ newSys := *sysAttr // copy
+ newSys.PidFD = &pidfd
+ return &newSys
+ }
+
+ return sysAttr
+}
+
+func getPidfd(sysAttr *syscall.SysProcAttr) uintptr {
+ if !pidfdWorks() {
+ return unsetHandle
+ }
+
+ return uintptr(*sysAttr.PidFD)
+}
+
+func (p *Process) pidfdRelease() {
+ // Release pidfd unconditionally.
+ handle := p.handle.Swap(unsetHandle)
+ if handle != unsetHandle {
+ syscall.Close(int(handle))
+ }
+}
+
+// _P_PIDFD is used as idtype argument to waitid syscall.
+const _P_PIDFD = 3
+
+func (p *Process) pidfdWait() (*ProcessState, error) {
+ handle := p.handle.Load()
+ if handle == unsetHandle || !pidfdWorks() {
+ return nil, syscall.ENOSYS
+ }
+ var (
+ info unix.SiginfoChild
+ rusage syscall.Rusage
+ e syscall.Errno
+ )
+ for {
+ _, _, e = syscall.Syscall6(syscall.SYS_WAITID, _P_PIDFD, handle, uintptr(unsafe.Pointer(&info)), syscall.WEXITED, uintptr(unsafe.Pointer(&rusage)), 0)
+ if e != syscall.EINTR {
+ break
+ }
+ }
+ if e != 0 {
+ if e == syscall.EINVAL {
+ // This is either invalid option value (which should not happen
+ // as we only use WEXITED), or missing P_PIDFD support (Linux
+ // kernel < 5.4), meaning pidfd support is not implemented.
+ e = syscall.ENOSYS
+ }
+ return nil, e
+ }
+ p.setDone()
+ p.pidfdRelease()
+ return &ProcessState{
+ pid: int(info.Pid),
+ status: info.WaitStatus(),
+ rusage: &rusage,
+ }, nil
+}
+
+func (p *Process) pidfdSendSignal(s syscall.Signal) error {
+ handle := p.handle.Load()
+ if handle == unsetHandle || !pidfdWorks() {
+ return syscall.ENOSYS
+ }
+ return convertESRCH(unix.PidFDSendSignal(handle, s))
+}
+
+func pidfdWorks() bool {
+ return checkPidfdOnce() == nil
+}
+
+var checkPidfdOnce = sync.OnceValue(checkPidfd)
+
+// checkPidfd checks whether all required pidfd-related syscalls work.
+// This consists of pidfd_open and pidfd_send_signal syscalls, and waitid
+// syscall with idtype of P_PIDFD.
+//
+// Reasons for non-working pidfd syscalls include an older kernel and an
+// execution environment in which the above system calls are restricted by
+// seccomp or a similar technology.
+func checkPidfd() error {
+ // Get a pidfd of the current process (opening of "/proc/self" won't
+ // work for waitid).
+ fd, err := unix.PidFDOpen(syscall.Getpid(), 0)
+ if err != nil {
+ return NewSyscallError("pidfd_open", err)
+ }
+ defer syscall.Close(int(fd))
+
+ // Check waitid(P_PIDFD) works.
+ for {
+ _, _, err = syscall.Syscall6(syscall.SYS_WAITID, _P_PIDFD, fd, 0, syscall.WEXITED, 0, 0)
+ if err != syscall.EINTR {
+ break
+ }
+ }
+ // Expect ECHILD from waitid since we're not our own parent.
+ if err != syscall.ECHILD {
+ return NewSyscallError("pidfd_wait", err)
+ }
+
+ // Check pidfd_send_signal works (should be able to send 0 to itself).
+ if err := unix.PidFDSendSignal(fd, 0); err != nil {
+ return NewSyscallError("pidfd_send_signal", err)
+ }
+
+ return nil
+}
diff --git a/src/os/pidfd_linux_test.go b/src/os/pidfd_linux_test.go
new file mode 100644
index 0000000..d003e8c
--- /dev/null
+++ b/src/os/pidfd_linux_test.go
@@ -0,0 +1,20 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package os_test
+
+import (
+ "os"
+ "testing"
+)
+
+func TestCheckPidfd(t *testing.T) {
+ // This doesn't test anything, but merely allows to check that pidfd
+ // is working (and thus being tested) in CI on some platforms.
+ if err := os.CheckPidfdOnce(); err != nil {
+ t.Log("checkPidfd:", err)
+ } else {
+ t.Log("pidfd syscalls work")
+ }
+}
diff --git a/src/os/pidfd_other.go b/src/os/pidfd_other.go
new file mode 100644
index 0000000..1918acb
--- /dev/null
+++ b/src/os/pidfd_other.go
@@ -0,0 +1,27 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build (unix && !linux) || (js && wasm) || wasip1 || windows
+
+package os
+
+import "syscall"
+
+func ensurePidfd(sysAttr *syscall.SysProcAttr) *syscall.SysProcAttr {
+ return sysAttr
+}
+
+func getPidfd(_ *syscall.SysProcAttr) uintptr {
+ return unsetHandle
+}
+
+func (p *Process) pidfdRelease() {}
+
+func (_ *Process) pidfdWait() (*ProcessState, error) {
+ return nil, syscall.ENOSYS
+}
+
+func (_ *Process) pidfdSendSignal(_ syscall.Signal) error {
+ return syscall.ENOSYS
+}
