syscall: make origRlimitNofile atomic.Pointer[Rlimit]

Currently we are bootstrapping with Go 1.20, origRlimitNofile can
be changed to atomic.Pointer[Rlimit].

Change-Id: I00ce9d1a9030bd5dbd34e3dc6c4e38683a87be86
GitHub-Last-Rev: f2ccdb3841
GitHub-Pull-Request: golang/go#63274
Reviewed-on: https://go-review.googlesource.com/c/go/+/531516
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: qiulaidongfeng <2645477756@qq.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>

src/syscall/exec_bsd.go

@@ -64,7 +64,7 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 		ngroups, groups uintptr
 	)
 
-	rlim, rlimOK := origRlimitNofile.Load().(Rlimit)
+	rlim := origRlimitNofile.Load()
 
 	// guard against side effects of shuffling fds below.
 	// Make sure that nextfd is beyond any currently open files so
@@ -276,8 +276,8 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 	}
 
 	// Restore original rlimit.
-	if rlimOK && rlim.Cur != 0 {
-		RawSyscall(SYS_SETRLIMIT, uintptr(RLIMIT_NOFILE), uintptr(unsafe.Pointer(&rlim)), 0)
+	if rlim != nil {
+		RawSyscall(SYS_SETRLIMIT, uintptr(RLIMIT_NOFILE), uintptr(unsafe.Pointer(rlim)), 0)
 	}
 
 	// Time to exec.

src/syscall/exec_freebsd.go

@@ -71,7 +71,7 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 		upid            uintptr
 	)
 
-	rlim, rlimOK := origRlimitNofile.Load().(Rlimit)
+	rlim := origRlimitNofile.Load()
 
 	// Record parent PID so child can test if it has died.
 	ppid, _, _ := RawSyscall(SYS_GETPID, 0, 0, 0)
@@ -300,8 +300,8 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 	}
 
 	// Restore original rlimit.
-	if rlimOK && rlim.Cur != 0 {
-		RawSyscall(SYS_SETRLIMIT, uintptr(RLIMIT_NOFILE), uintptr(unsafe.Pointer(&rlim)), 0)
+	if rlim != nil {
+		RawSyscall(SYS_SETRLIMIT, uintptr(RLIMIT_NOFILE), uintptr(unsafe.Pointer(rlim)), 0)
 	}
 
 	// Time to exec.

src/syscall/exec_libc.go

@@ -91,7 +91,7 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 		ngroups, groups uintptr
 	)
 
-	rlim, rlimOK := origRlimitNofile.Load().(Rlimit)
+	rlim := origRlimitNofile.Load()
 
 	// guard against side effects of shuffling fds below.
 	// Make sure that nextfd is beyond any currently open files so
@@ -296,8 +296,8 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 	}
 
 	// Restore original rlimit.
-	if rlimOK && rlim.Cur != 0 {
-		setrlimit1(RLIMIT_NOFILE, unsafe.Pointer(&rlim))
+	if rlim != nil {
+		setrlimit1(RLIMIT_NOFILE, unsafe.Pointer(rlim))
 	}
 
 	// Time to exec.

src/syscall/exec_libc2.go

@@ -65,7 +65,7 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 		ngroups, groups uintptr
 	)
 
-	rlim, rlimOK := origRlimitNofile.Load().(Rlimit)
+	rlim := origRlimitNofile.Load()
 
 	// guard against side effects of shuffling fds below.
 	// Make sure that nextfd is beyond any currently open files so
@@ -272,8 +272,8 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 	}
 
 	// Restore original rlimit.
-	if rlimOK && rlim.Cur != 0 {
-		rawSyscall(abi.FuncPCABI0(libc_setrlimit_trampoline), uintptr(RLIMIT_NOFILE), uintptr(unsafe.Pointer(&rlim)), 0)
+	if rlim != nil {
+		rawSyscall(abi.FuncPCABI0(libc_setrlimit_trampoline), uintptr(RLIMIT_NOFILE), uintptr(unsafe.Pointer(rlim)), 0)
 	}
 
 	// Time to exec.

src/syscall/exec_linux.go

@@ -248,7 +248,7 @@ func forkAndExecInChild1(argv0 *byte, argv, envv []*byte, chroot, dir *byte, att
 		c                         uintptr
 	)
 
-	rlim, rlimOK := origRlimitNofile.Load().(Rlimit)
+	rlim := origRlimitNofile.Load()
 
 	if sys.UidMappings != nil {
 		puid = []byte("/proc/self/uid_map\000")
@@ -628,8 +628,8 @@ func forkAndExecInChild1(argv0 *byte, argv, envv []*byte, chroot, dir *byte, att
 	}
 
 	// Restore original rlimit.
-	if rlimOK && rlim.Cur != 0 {
-		rawSetrlimit(RLIMIT_NOFILE, &rlim)
+	if rlim != nil {
+		rawSetrlimit(RLIMIT_NOFILE, rlim)
 	}
 
 	// Enable tracing if requested.

src/syscall/exec_unix.go

@@ -281,9 +281,9 @@ func Exec(argv0 string, argv []string, envv []string) (err error) {
 	}
 	runtime_BeforeExec()
 
-	rlim, rlimOK := origRlimitNofile.Load().(Rlimit)
-	if rlimOK && rlim.Cur != 0 {
-		Setrlimit(RLIMIT_NOFILE, &rlim)
+	rlim := origRlimitNofile.Load()
+	if rlim != nil {
+		Setrlimit(RLIMIT_NOFILE, rlim)
 	}
 
 	var err1 error

src/syscall/export_rlimit_test.go

@@ -7,8 +7,8 @@
 package syscall
 
 func OrigRlimitNofile() Rlimit {
-	if rlim, ok := origRlimitNofile.Load().(Rlimit); ok {
-		return rlim
+	if rlim := origRlimitNofile.Load(); rlim != nil {
+		return *rlim
 	}
 	return Rlimit{0, 0}
 }

src/syscall/rlimit.go

@@ -10,10 +10,8 @@ import (
 	"sync/atomic"
 )
 
-// origRlimitNofile, if not {0, 0}, is the original soft RLIMIT_NOFILE.
-// When we can assume that we are bootstrapping with Go 1.19,
-// this can be atomic.Pointer[Rlimit].
-var origRlimitNofile atomic.Value // of Rlimit
+// origRlimitNofile, if non-nil, is the original soft RLIMIT_NOFILE.
+var origRlimitNofile atomic.Pointer[Rlimit]
 
 // Some systems set an artificially low soft limit on open file count, for compatibility
 // with code that uses select and its hard-coded maximum file descriptor
@@ -32,7 +30,7 @@ var origRlimitNofile atomic.Value // of Rlimit
 func init() {
 	var lim Rlimit
 	if err := Getrlimit(RLIMIT_NOFILE, &lim); err == nil && lim.Cur != lim.Max {
-		origRlimitNofile.Store(lim)
+		origRlimitNofile.Store(&lim)
 		lim.Cur = lim.Max
 		adjustFileLimit(&lim)
 		setrlimit(RLIMIT_NOFILE, &lim)
@@ -42,9 +40,9 @@ func init() {
 func Setrlimit(resource int, rlim *Rlimit) error {
 	err := setrlimit(resource, rlim)
 	if err == nil && resource == RLIMIT_NOFILE {
-		// Store zeroes in origRlimitNofile to tell StartProcess
+		// Store nil in origRlimitNofile to tell StartProcess
 		// to not adjust the rlimit in the child process.
-		origRlimitNofile.Store(Rlimit{0, 0})
+		origRlimitNofile.Store(nil)
 	}
 	return err
 }

src/syscall/syscall_linux.go

@@ -1277,7 +1277,7 @@ func Munmap(b []byte) (err error) {
 func prlimit(pid int, resource int, newlimit *Rlimit, old *Rlimit) (err error) {
 	err = prlimit1(pid, resource, newlimit, old)
 	if err == nil && newlimit != nil && resource == RLIMIT_NOFILE {
-		origRlimitNofile.Store(Rlimit{0, 0})
+		origRlimitNofile.Store(nil)
 	}
 	return err
 }