libct: fix resetting CPU affinity

unix.CPUSet is limited to 1024 CPUs. Calling
unix.SchedSetaffinity(pid, cpuset) removes all CPUs starting from 1024
from allowed CPUs of pid, even if cpuset is all ones. As a
consequence, when runc tries to reset CPU affinity to "allow all" by
default, it prevents all containers from CPUs 1024 onwards.

This change uses a huge CPU mask to play safe and get all possible
CPUs enabled with a single sched_setaffinity call.

Fixes: #5023

Signed-off-by: Antti Kervinen <antti.kervinen@intel.com>
(cherry picked from commit 700c944c4d)
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

internal/linux/linux.go

@@ -2,6 +2,7 @@ package linux
 
 import (
 	"os"
+	"unsafe"
 
 	"golang.org/x/sys/unix"
 )
@@ -65,6 +66,22 @@ func Recvfrom(fd int, p []byte, flags int) (n int, from unix.Sockaddr, err error
 	return n, from, err
 }
 
+// SchedSetaffinity wraps sched_setaffinity syscall without unix.CPUSet size limitation.
+func SchedSetaffinity(pid int, buf []byte) error {
+	err := retryOnEINTR(func() error {
+		_, _, errno := unix.Syscall(
+			unix.SYS_SCHED_SETAFFINITY,
+			uintptr(pid),
+			uintptr(len(buf)),
+			uintptr((unsafe.Pointer)(&buf[0])))
+		if errno != 0 {
+			return errno
+		}
+		return nil
+	})
+	return os.NewSyscallError("sched_setaffinity", err)
+}
+
 // Sendmsg wraps [unix.Sendmsg].
 func Sendmsg(fd int, p, oob []byte, to unix.Sockaddr, flags int) error {
 	err := retryOnEINTR(func() error {