libct: use CPUSetDynamic for affinity and mempolicy masks

ToCPUSet was limited to unix.CPUSet (a fixed-size mask capped at 1024
CPUs). Switch CPUAffinity, LinuxMemoryPolicy.Nodes, ToCPUSet, and
SetMempolicy to unix.CPUSetDynamic, which can represent arbitrary CPU
and NUMA node IDs.

ToCPUSet now parses the input in a first pass to find the maximum value,
then allocates a mask large enough to hold it (out-of-range Set calls on
a dynamic mask are silently ignored). An arbitrary sanity cap is kept to
avoid huge allocations on bogus input.

This is backward compatible with reading older state.json: both the old
*unix.CPUSet (a fixed array) and the new CPUSetDynamic (a slice)
marshal to and from the same JSON array-of-numbers representation.

Update TestToCPUSet accordingly, adding coverage for values beyond the
old non-dynamic limit.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

Author: kolyshkin

CHANGELOG.md

@@ -6,12 +6,20 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### libcontainer API ###
+- `configs.ToCPUSet` now returns a `unix.CPUSetDynamic` instead of a
+  `*unix.CPUSet`, and the `Initial`/`Final` fields of `configs.CPUAffinity` and
+  the `Nodes` field of `configs.LinuxMemoryPolicy` have changed type
+  accordingly. This lifts the previous 1024 CPUs/nodes limit. (#5343)
+
 ### Fixed ###
 - The poststart hooks are now executed after starting the user-specified
   process, fixing a runtime-spec conformance issue. (#4347, #5186)
 
 ### Changed ###
 - Updated builds to libseccomp v2.6.1. (#5376)
+- The `cpuAffinity` and NUMA `memoryPolicy` settings are no longer limited
+  to 1024 CPUs/nodes, as runc now uses a dynamically-sized CPU mask. (#5343)
 
 ## [1.5.0] - 2026-06-19
 

internal/linux/linux.go

@@ -81,10 +81,10 @@ func Sendmsg(fd int, p, oob []byte, to unix.Sockaddr, flags int) error {
 	return os.NewSyscallError("sendmsg", err)
 }
 
-// SetMempolicy wraps set_mempolicy.
-func SetMempolicy(mode int, mask *unix.CPUSet) error {
+// SetMempolicy wraps [unix.SetMempolicyDynamic].
+func SetMempolicy(mode int, mask unix.CPUSetDynamic) error {
 	err := retryOnEINTR(func() error {
-		return unix.SetMemPolicy(mode, mask)
+		return unix.SetMemPolicyDynamic(mode, mask)
 	})
 	return os.NewSyscallError("set_mempolicy", err)
 }

libcontainer/configs/config.go

@@ -11,7 +11,6 @@ import (
 	"strconv"
 	"strings"
 	"time"
-	"unsafe"
 
 	"github.com/sirupsen/logrus"
 	"golang.org/x/sys/unix"
@@ -305,26 +304,53 @@ func ToSchedAttr(scheduler *Scheduler) (*unix.SchedAttr, error) {
 type IOPriority = specs.LinuxIOPriority
 
 type CPUAffinity struct {
-	Initial, Final *unix.CPUSet
+	Initial, Final unix.CPUSetDynamic
 }
 
-// ToCPUSet parses a string in list format into a unix.CPUSet, e.g. "0-3,5,7-9".
-func ToCPUSet(str string) (*unix.CPUSet, error) {
+// maxCPUSetCPU is the highest CPU/NUMA node ID that [ToCPUSet] accepts. It is
+// an arbitrary sanity limit, used to avoid allocating an unreasonably large
+// mask for a bogus input.
+const maxCPUSetCPU = 64 * 1024
+
+// ToCPUSet parses a string in list format into a [unix.CPUSetDynamic],
+// e.g. "0-3,5,7-9".
+func ToCPUSet(str string) (unix.CPUSetDynamic, error) {
 	if str == "" {
 		return nil, nil
 	}
-	s := new(unix.CPUSet)
 
-	// Since (*CPUset).Set silently ignores too high CPU values,
-	// find out what the maximum is, and return an error.
-	maxCPU := uint64(unsafe.Sizeof(*s) * 8)
+	maxCPU, ranges, err := cpuStrToRanges(str)
+	if err != nil {
+		return nil, err
+	}
+	if len(ranges) == 0 {
+		return nil, fmt.Errorf("no members found in set %q", str)
+	}
+
+	s := unix.NewCPUSet(maxCPU + 1)
+	for _, cr := range ranges {
+		for i := cr.start; i <= cr.end; i++ {
+			s.Set(i)
+		}
+	}
+
+	return s, nil
+}
+
+type cpuRange struct {
+	start, end int
+}
+
+// cpuStrToRanges parses string (e.g. "0-3,5,7-9") into a slice of cpuRange
+// values. It also returns the maximum value and an error, if any.
+func cpuStrToRanges(str string) (maxCPU int, ranges []cpuRange, _ error) {
 	toInt := func(v string) (int, error) {
 		ret, err := strconv.ParseUint(v, 10, 32)
 		if err != nil {
 			return 0, err
 		}
-		if ret >= maxCPU {
-			return 0, fmt.Errorf("values larger than %d are not supported", maxCPU-1)
+		if ret > maxCPUSetCPU {
+			return 0, fmt.Errorf("values larger than %d are not supported", maxCPUSetCPU)
 		}
 		return int(ret), nil
 	}
@@ -336,34 +362,27 @@ func ToCPUSet(str string) (*unix.CPUSet, error) {
 		if r == "" {
 			continue
 		}
-		if r0, r1, found := strings.Cut(r, "-"); found {
-			start, err := toInt(r0)
-			if err != nil {
-				return nil, err
-			}
-			end, err := toInt(r1)
-			if err != nil {
-				return nil, err
-			}
-			if start > end {
-				return nil, errors.New("invalid range: " + r)
+		start, end, found := strings.Cut(r, "-")
+		cr := cpuRange{}
+		var err error
+		if cr.start, err = toInt(start); err != nil {
+			return 0, nil, err
+		}
+		if found {
+			if cr.end, err = toInt(end); err != nil {
+				return 0, nil, err
 			}
-			for i := start; i <= end; i++ {
-				s.Set(i)
+			if cr.start > cr.end {
+				return 0, nil, errors.New("invalid range: " + r)
 			}
 		} else {
-			val, err := toInt(r)
-			if err != nil {
-				return nil, err
-			}
-			s.Set(val)
+			cr.end = cr.start
 		}
-	}
-	if s.Count() == 0 {
-		return nil, fmt.Errorf("no members found in set %q", str)
+		maxCPU = max(maxCPU, cr.end)
+		ranges = append(ranges, cr)
 	}
 
-	return s, nil
+	return maxCPU, ranges, nil
 }
 
 // ConvertCPUAffinity converts [specs.CPUAffinity] to [CPUAffinity].

libcontainer/configs/memorypolicy.go

@@ -10,5 +10,5 @@ type LinuxMemoryPolicy struct {
 	// Flags contains mode flags.
 	Flags int `json:"flags,omitempty"`
 	// Nodes contains NUMA nodes to which the mode applies.
-	Nodes *unix.CPUSet `json:"nodes,omitempty"`
+	Nodes unix.CPUSetDynamic `json:"nodes,omitempty"`
 }

libcontainer/configs/tocpuset_test.go

@@ -1,47 +1,67 @@
 package configs
 
 import (
+	"slices"
 	"testing"
 
 	"golang.org/x/sys/unix"
 )
 
 func TestToCPUSet(t *testing.T) {
-	set := func(cpus ...int) *unix.CPUSet {
-		r := &unix.CPUSet{}
+	set := func(cpus ...int) unix.CPUSetDynamic {
+		maxCPU := 0
+		for _, cpu := range cpus {
+			maxCPU = max(maxCPU, cpu)
+		}
+		r := unix.NewCPUSet(maxCPU + 1)
 		for _, cpu := range cpus {
 			r.Set(cpu)
 		}
 		return r
 	}
 
+	// trim removes trailing all-zero masks so that sets representing the
+	// same CPUs compare equal regardless of how they were allocated.
+	trim := func(s unix.CPUSetDynamic) unix.CPUSetDynamic {
+		for len(s) > 0 && s[len(s)-1] == 0 {
+			s = s[:len(s)-1]
+		}
+		return s
+	}
+
 	testCases := []struct {
 		in    string
-		out   *unix.CPUSet
+		out   unix.CPUSetDynamic
 		isErr bool
 	}{
 		{in: ""}, // Empty means unset.
 
 		// Valid cases.
-		{in: "0", out: &unix.CPUSet{1}},
-		{in: "1", out: &unix.CPUSet{2}},
-		{in: "0-1", out: &unix.CPUSet{3}},
-		{in: "0,1", out: &unix.CPUSet{3}},
-		{in: ",0,1,", out: &unix.CPUSet{3}},
-		{in: "0-3", out: &unix.CPUSet{0x0f}},
-		{in: "0,1,2-3", out: &unix.CPUSet{0x0f}},
-		{in: "4-7", out: &unix.CPUSet{0xf0}},
-		{in: "0-7", out: &unix.CPUSet{0xff}},
-		{in: "0-15", out: &unix.CPUSet{0xffff}},
-		{in: "16", out: &unix.CPUSet{0x10000}},
+		{in: "0", out: set(0)},
+		{in: "1", out: set(1)},
+		{in: "0-1", out: set(0, 1)},
+		{in: "0,1", out: set(0, 1)},
+		{in: ",0,1,", out: set(0, 1)},
+		{in: "0-3", out: set(0, 1, 2, 3)},
+		{in: "0,1,2-3", out: set(0, 1, 2, 3)},
+		{in: "4-7", out: set(4, 5, 6, 7)},
+		{in: "0-7", out: set(0, 1, 2, 3, 4, 5, 6, 7)},
+		{in: "0-15", out: set(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)},
+		{in: "16", out: set(16)},
 		// Extra whitespace in between ranges are OK.
-		{in: "1, 2, 1-2", out: &unix.CPUSet{6}},
-		{in: "    , 1   , 3  ,  5-7,    ", out: &unix.CPUSet{0xea}},
-		// Somewhat large values. The underlying type in unix.CPUSet
-		// can either be uint32 or uint64, so we have to use a helper.
+		{in: "1, 2, 1-2", out: set(1, 2)},
+		{in: "    , 1   , 3  ,  5-7,    ", out: set(1, 3, 5, 6, 7)},
+		// Somewhat large values.
 		{in: "0-3,32-33", out: set(0, 1, 2, 3, 32, 33)},
 		{in: "127-129, 1", out: set(1, 127, 128, 129)},
 		{in: "1023", out: set(1023)},
+		// Values larger than what a (non-dynamic) unix.CPUSet can hold.
+		{in: "1024", out: set(1024)},
+		{in: "8191", out: set(8191)},
+		{in: "4096-4098", out: set(4096, 4097, 4098)},
+		{in: "0,65536", out: set(0, 65536)},
+		// Maximum allowed value.
+		{in: "65536", out: set(65536)},
 
 		// Error cases.
 		{in: "-", isErr: true},
@@ -53,7 +73,9 @@ func TestToCPUSet(t *testing.T) {
 		{in: "54-53", isErr: true},
 		// Extra spaces inside a range is not OK.
 		{in: "1 - 2", isErr: true},
-		{in: "1024", isErr: true}, // Too big for unix.CPUSet.
+		// Larger than the maximum supported value.
+		{in: "65537", isErr: true},
+		{in: "0-65537", isErr: true},
 	}
 
 	for _, tc := range testCases {
@@ -80,7 +102,7 @@ func TestToCPUSet(t *testing.T) {
 			if out == nil {
 				t.Fatalf("want %v, got nil", tc.out)
 			}
-			if *out != *tc.out {
+			if !slices.Equal(trim(out), trim(tc.out)) {
 				t.Errorf("case %q: want %v, got %v", tc.in, tc.out, out)
 			}
 		})

libcontainer/process_linux.go

@@ -224,7 +224,7 @@ func (p *setnsProcess) startWithCPUAffinity() error {
 	go func() {
 		runtime.LockOSThread()
 		// Command inherits the CPU affinity.
-		if err := unix.SchedSetaffinity(unix.Gettid(), aff.Initial); err != nil {
+		if err := linux.SchedSetaffinity(unix.Gettid(), aff.Initial); err != nil {
 			errCh <- fmt.Errorf("error setting initial CPU affinity: %w", err)
 			return
 		}
@@ -250,7 +250,7 @@ func (p *setnsProcess) setFinalCPUAffinity() error {
 	if aff.Final == nil {
 		return nil
 	}
-	if err := unix.SchedSetaffinity(p.pid(), aff.Final); err != nil {
+	if err := linux.SchedSetaffinity(p.pid(), aff.Final); err != nil {
 		return fmt.Errorf("error setting final CPU affinity: %w", err)
 	}
 	return nil