[BISECTED][REGRESSION] 5.10.56 longterm kernel breakage on m68k/aranym

[Mikael Pettersson <mikpelinux@gmail.com>]

I updated the 5.10 longterm kernel on one of my m68k/aranym VMs from
5.10.47 to 5.10.56, and the new kernel failed to boot:

ARAnyM 1.1.0
Using config file: 'aranym1.headless.config'
Could not open joystick 0
ARAnyM RTC Timer: /dev/rtc: Permission denied
ARAnyM LILO: Error loading ramdisk 'root.bin'
Blitter tried to read byte from register ff8a00 at 0077ee

At this point it kept running, but produced no output to the console,
and would never get to the point of starting user-space. Attaching gdb
to aranym showed nothing interesting, i.e. it seemed to be executing
normally.

A git bisect identified the following commit between 5.10.52 and
5.10.53 as the culprit:
# first bad commit: [9e1cf2d1ed37c934c9935f2c0b2f8b15d9355654]
mm/userfaultfd: fix uffd-wp special cases for fork()

5.10.52, 5.11.22, 5.12.19, and 5.13.8 all boot fine. 5.10.53 to
5.10.56 all fail as described above.

grep ^CONFIG .config below, everything omitted is of course disabled,
including I might add CONFIG_USERFAULTFD.

/Mikael

CONFIG_CC_VERSION_TEXT="m68k-unknown-linux-gcc (GCC) 10.3.1 20210424"
CONFIG_CC_IS_GCC=y
CONFIG_GCC_VERSION=100301
CONFIG_LD_VERSION=231010000
CONFIG_CLANG_VERSION=0
CONFIG_LLD_VERSION=0
CONFIG_CC_CAN_LINK=y
CONFIG_CC_CAN_LINK_STATIC=y
CONFIG_CC_HAS_ASM_GOTO=y
CONFIG_CC_HAS_ASM_INLINE=y
CONFIG_IRQ_WORK=y
CONFIG_BROKEN_ON_SMP=y
CONFIG_INIT_ENV_ARG_LIMIT=32
CONFIG_LOCALVERSION=""
CONFIG_BUILD_SALT=""
CONFIG_DEFAULT_INIT=""
CONFIG_DEFAULT_HOSTNAME="(none)"
CONFIG_SWAP=y
CONFIG_SYSVIPC=y
CONFIG_SYSVIPC_SYSCTL=y
CONFIG_GENERIC_IRQ_SHOW=y
CONFIG_PREEMPT_NONE=y
CONFIG_TICK_CPU_ACCOUNTING=y
CONFIG_TINY_RCU=y
CONFIG_SRCU=y
CONFIG_TINY_SRCU=y
CONFIG_LOG_BUF_SHIFT=15
CONFIG_PRINTK_SAFE_LOG_BUF_SHIFT=13
CONFIG_CGROUPS=y
CONFIG_BLK_DEV_INITRD=y
CONFIG_INITRAMFS_SOURCE=""
CONFIG_RD_GZIP=y
CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE=y
CONFIG_SYSCTL=y
CONFIG_HAVE_UID16=y
CONFIG_BPF=y
CONFIG_EXPERT=y
CONFIG_UID16=y
CONFIG_MULTIUSER=y
CONFIG_FHANDLE=y
CONFIG_POSIX_TIMERS=y
CONFIG_PRINTK=y
CONFIG_BUG=y
CONFIG_ELF_CORE=y
CONFIG_BASE_FULL=y
CONFIG_FUTEX=y
CONFIG_FUTEX_PI=y
CONFIG_HAVE_FUTEX_CMPXCHG=y
CONFIG_EPOLL=y
CONFIG_SIGNALFD=y
CONFIG_TIMERFD=y
CONFIG_EVENTFD=y
CONFIG_SHMEM=y
CONFIG_ADVISE_SYSCALLS=y
CONFIG_KALLSYMS=y
CONFIG_KALLSYMS_BASE_RELATIVE=y
CONFIG_EMBEDDED=y
CONFIG_SLUB=y
CONFIG_SLAB_MERGE_DEFAULT=y
CONFIG_M68K=y
CONFIG_CPU_BIG_ENDIAN=y
CONFIG_GENERIC_HWEIGHT=y
CONFIG_GENERIC_CALIBRATE_DELAY=y
CONFIG_TIME_LOW_RES=y
CONFIG_NO_IOPORT_MAP=y
CONFIG_ZONE_DMA=y
CONFIG_HZ=100
CONFIG_PGTABLE_LEVELS=3
CONFIG_MMU=y
CONFIG_MMU_MOTOROLA=y
CONFIG_M68KCLASSIC=y
CONFIG_M68020=y
CONFIG_M68030=y
CONFIG_M68040=y
CONFIG_M68060=y
CONFIG_M68KFPU_EMU=y
CONFIG_M68KFPU_EMU_EXTRAPREC=y
CONFIG_ADVANCED=y
CONFIG_RMW_INSNS=y
CONFIG_ARCH_DISCONTIGMEM_ENABLE=y
CONFIG_NODES_SHIFT=3
CONFIG_CPU_HAS_ADDRESS_SPACES=y
CONFIG_FPU=y
CONFIG_ATARI=y
CONFIG_ATARI_KBD_CORE=y
CONFIG_PROC_HARDWARE=y
CONFIG_NATFEAT=y
CONFIG_NFBLOCK=y
CONFIG_NFCON=y
CONFIG_NFETH=y
CONFIG_CRASH_CORE=y
CONFIG_SET_FS=y
CONFIG_ARCH_32BIT_OFF_T=y
CONFIG_HAVE_ASM_MODVERSIONS=y
CONFIG_MMU_GATHER_NO_RANGE=y
CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG=y
CONFIG_ARCH_WANT_IPC_PARSE_VERSION=y
CONFIG_HAVE_MOD_ARCH_SPECIFIC=y
CONFIG_MODULES_USE_ELF_RELA=y
CONFIG_MODULES_USE_ELF_REL=y
CONFIG_HAVE_ARCH_NVRAM_OPS=y
CONFIG_OLD_SIGSUSPEND3=y
CONFIG_OLD_SIGACTION=y
CONFIG_COMPAT_32BIT_TIME=y
CONFIG_ARCH_NO_PREEMPT=y
CONFIG_RT_MUTEXES=y
CONFIG_BASE_SMALL=0
CONFIG_MODULES=y
CONFIG_MODULE_UNLOAD=y
CONFIG_BLOCK=y
CONFIG_BLK_SCSI_REQUEST=y
CONFIG_BLK_DEV_BSG=y
CONFIG_PARTITION_ADVANCED=y
CONFIG_ATARI_PARTITION=y
CONFIG_MSDOS_PARTITION=y
CONFIG_INLINE_SPIN_UNLOCK_IRQ=y
CONFIG_INLINE_READ_UNLOCK=y
CONFIG_INLINE_READ_UNLOCK_IRQ=y
CONFIG_INLINE_WRITE_UNLOCK=y
CONFIG_INLINE_WRITE_UNLOCK_IRQ=y
CONFIG_BINFMT_ELF=y
CONFIG_ELFCORE=y
CONFIG_CORE_DUMP_DEFAULT_ELF_HEADERS=y
CONFIG_BINFMT_SCRIPT=y
CONFIG_ARCH_HAS_BINFMT_FLAT=y
CONFIG_BINFMT_FLAT_ARGVP_ENVP_ON_STACK=y
CONFIG_HAVE_AOUT=y
CONFIG_COREDUMP=y
CONFIG_DISCONTIGMEM=y
CONFIG_FLAT_NODE_MEM_MAP=y
CONFIG_NEED_MULTIPLE_NODES=y
CONFIG_SPLIT_PTLOCK_CPUS=4
CONFIG_BOUNCE=y
CONFIG_VIRT_TO_BUS=y
CONFIG_DEFAULT_MMAP_MIN_ADDR=4096
CONFIG_NEED_PER_CPU_KM=y
CONFIG_NET=y
CONFIG_PACKET=y
CONFIG_UNIX=y
CONFIG_UNIX_SCM=y
CONFIG_INET=y
CONFIG_TCP_CONG_CUBIC=y
CONFIG_DEFAULT_TCP_CONG="cubic"
CONFIG_IPV6=m
CONFIG_HAVE_NET_DSA=y
CONFIG_NET_RX_BUSY_POLL=y
CONFIG_BQL=y
CONFIG_DEVTMPFS=y
CONFIG_DEVTMPFS_MOUNT=y
CONFIG_STANDALONE=y
CONFIG_PREVENT_FIRMWARE_BUILD=y
CONFIG_GENERIC_CPU_DEVICES=y
CONFIG_BLK_DEV=y
CONFIG_BLK_DEV_LOOP=m
CONFIG_BLK_DEV_LOOP_MIN_COUNT=8
CONFIG_HAVE_IDE=y
CONFIG_SCSI_MOD=y
CONFIG_NETDEVICES=y
CONFIG_ETHERNET=y
CONFIG_INPUT=y
CONFIG_INPUT_MOUSEDEV=y
CONFIG_INPUT_MOUSEDEV_SCREEN_X=1024
CONFIG_INPUT_MOUSEDEV_SCREEN_Y=768
CONFIG_INPUT_EVDEV=m
CONFIG_INPUT_KEYBOARD=y
CONFIG_KEYBOARD_ATARI=y
CONFIG_INPUT_MOUSE=y
CONFIG_MOUSE_ATARI=y
CONFIG_INPUT_MISC=y
CONFIG_INPUT_M68K_BEEP=y
CONFIG_TTY=y
CONFIG_VT=y
CONFIG_CONSOLE_TRANSLATIONS=y
CONFIG_VT_CONSOLE=y
CONFIG_HW_CONSOLE=y
CONFIG_VT_HW_CONSOLE_BINDING=y
CONFIG_UNIX98_PTYS=y
CONFIG_LDISC_AUTOLOAD=y
CONFIG_NVRAM=y
CONFIG_SSB_POSSIBLE=y
CONFIG_BCMA_POSSIBLE=y
CONFIG_FB_CMDLINE=y
CONFIG_FB_NOTIFY=y
CONFIG_FB=y
CONFIG_FB_CFB_FILLRECT=y
CONFIG_FB_CFB_COPYAREA=y
CONFIG_FB_CFB_IMAGEBLIT=y
CONFIG_FB_ATARI=y
CONFIG_DUMMY_CONSOLE=y
CONFIG_DUMMY_CONSOLE_COLUMNS=80
CONFIG_DUMMY_CONSOLE_ROWS=25
CONFIG_FRAMEBUFFER_CONSOLE=y
CONFIG_USB_OHCI_LITTLE_ENDIAN=y
CONFIG_RTC_LIB=y
CONFIG_RTC_CLASS=y
CONFIG_RTC_HCTOSYS=y
CONFIG_RTC_HCTOSYS_DEVICE="rtc0"
CONFIG_RTC_INTF_SYSFS=y
CONFIG_RTC_INTF_PROC=y
CONFIG_RTC_INTF_DEV=y
CONFIG_RTC_DRV_GENERIC=y
CONFIG_FS_IOMAP=y
CONFIG_EXT4_FS=y
CONFIG_EXT4_USE_FOR_EXT2=y
CONFIG_EXT4_FS_POSIX_ACL=y
CONFIG_EXT4_FS_SECURITY=y
CONFIG_JBD2=y
CONFIG_FS_MBCACHE=y
CONFIG_FS_POSIX_ACL=y
CONFIG_EXPORTFS=y
CONFIG_FILE_LOCKING=y
CONFIG_FSNOTIFY=y
CONFIG_DNOTIFY=y
CONFIG_INOTIFY_USER=y
CONFIG_FANOTIFY=y
CONFIG_PROC_FS=y
CONFIG_PROC_KCORE=y
CONFIG_PROC_SYSCTL=y
CONFIG_KERNFS=y
CONFIG_SYSFS=y
CONFIG_TMPFS=y
CONFIG_TMPFS_POSIX_ACL=y
CONFIG_TMPFS_XATTR=y
CONFIG_MEMFD_CREATE=y
CONFIG_SECURITY=y
CONFIG_HAVE_HARDENED_USERCOPY_ALLOCATOR=y
CONFIG_DEFAULT_SECURITY_DAC=y
CONFIG_LSM="lockdown,yama,loadpin,safesetid,integrity,bpf"
CONFIG_INIT_STACK_NONE=y
CONFIG_CRYPTO=y
CONFIG_CRYPTO_ALGAPI=y
CONFIG_CRYPTO_ALGAPI2=y
CONFIG_CRYPTO_HASH=y
CONFIG_CRYPTO_HASH2=y
CONFIG_CRYPTO_MANAGER_DISABLE_TESTS=y
CONFIG_CRYPTO_CRC32C=y
CONFIG_CRYPTO_AES=y
CONFIG_CRYPTO_LIB_AES=y
CONFIG_CRYPTO_LIB_POLY1305_RSIZE=1
CONFIG_BITREVERSE=y
CONFIG_GENERIC_STRNCPY_FROM_USER=y
CONFIG_GENERIC_STRNLEN_USER=y
CONFIG_GENERIC_NET_UTILS=y
CONFIG_GENERIC_PCI_IOMAP=y
CONFIG_GENERIC_IOMAP=y
CONFIG_CRC16=y
CONFIG_CRC32=y
CONFIG_CRC32_SLICEBY8=y
CONFIG_ZLIB_INFLATE=y
CONFIG_DECOMPRESS_GZIP=y
CONFIG_GENERIC_ALLOCATOR=y
CONFIG_HAS_IOMEM=y
CONFIG_HAS_DMA=y
CONFIG_ARCH_HAS_SYNC_DMA_FOR_DEVICE=y
CONFIG_ARCH_HAS_DMA_PREP_COHERENT=y
CONFIG_DMA_NONCOHERENT_MMAP=y
CONFIG_DMA_COHERENT_POOL=y
CONFIG_DMA_REMAP=y
CONFIG_DMA_DIRECT_REMAP=y
CONFIG_DQL=y
CONFIG_NLATTR=y
CONFIG_GENERIC_ATOMIC64=y
CONFIG_FONT_SUPPORT=y
CONFIG_FONT_8x8=y
CONFIG_FONT_8x16=y
CONFIG_SBITMAP=y
CONFIG_CONSOLE_LOGLEVEL_DEFAULT=7
CONFIG_CONSOLE_LOGLEVEL_QUIET=4
CONFIG_MESSAGE_LOGLEVEL_DEFAULT=4
CONFIG_DEBUG_BUGVERBOSE=y
CONFIG_ENABLE_MUST_CHECK=y
CONFIG_FRAME_WARN=1024
CONFIG_STRIP_ASM_SYMS=y
CONFIG_SECTION_MISMATCH_WARN_ONLY=y
CONFIG_MAGIC_SYSRQ=y
CONFIG_MAGIC_SYSRQ_DEFAULT_ENABLE=0x1
CONFIG_DEBUG_KERNEL=y
CONFIG_CC_HAS_WORKING_NOSANITIZE_ADDRESS=y
CONFIG_PANIC_ON_OOPS_VALUE=0
CONFIG_PANIC_TIMEOUT=0
CONFIG_HAVE_DEBUG_BUGVERBOSE=y
CONFIG_CC_HAS_SANCOV_TRACE_PC=y