I have the same problem, here is what I could find out so far:

I have an ext4 boot partition, the root partition is placed in a logical volume on an encrypted partition ("LVM on LUKS"). The latest working kernel is 4.17.14.arch1-1-x86_64, since 4.18.arch1-1-x86_64 I can't boot with the default initramfs, but with the fallback initramfs. Booting with the default initramfs and without the parameter "quiet" the following is shown:

:: running early hook [udev] starting version 239 :: running early hook [lvm2] :: running hook [udev] :: Triggering uevents...

This is where the system hangs. I would like to boot with the parameter "udev.log-priority=debug" to see what is going on, but the output just fills my screen too fast and I don't know how to scroll up. If this is where I can get further information, someone has to tell me what to do here.

Since booting with the fallback initramfs works, I did this with the parameter "break=postmount" so that I could get the output of

lsmod | awk 'NF==3{print $1}{}'

which is (alphabetically, but with "-" and "_" both written as "_" because my console font displays both as "_", so don't worry about that)

aes_x86_64 ahci algif_skcipher ata_generic crc32c_generic crypto_simd dm_crypt ehci_pci ext4 firewire_ohci glue_helper hid_generic pata_acpi pata_jmicron sd_mod sr_mod uhci_hcd usbhid xhci_pci xts

Then I used

$ bsdcpio -it usr/lib/modules < /boot/initramfs-linux.img

to get (alphabetically, and this time with correct "-" and "_")

usr/lib/modules usr/lib/modules/4.18.3-arch1-1-ARCH usr/lib/modules/4.18.3-arch1-1-ARCH/kernel usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/842_compress.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/842_decompress.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/842.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/aegis128-aesni.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/aegis128.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/aegis128l-aesni.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/aegis128l.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/aegis256-aesni.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/aegis256.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/aes_ti.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/aes-x86_64.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/aesni-intel.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/af_alg.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/ahci.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/algif_aead.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/algif_hash.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/algif_rng.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/algif_skcipher.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/ansi_cprng.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/anubis.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/arc4.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/async_memcpy.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/async_pq.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/async_raid6_recov.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/async_tx.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/async_xor.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/ata_generic.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/authenc.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/authencesn.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/blowfish_common.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/blowfish_generic.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/blowfish-x86_64.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/camellia_generic.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/camellia-aesni-avx-x86_64.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/camellia-aesni-avx2.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/camellia-x86_64.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/cast_common.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/cast5_generic.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/cast5-avx-x86_64.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/cast6_generic.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/cast6-avx-x86_64.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/cbc.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/ccm.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/ccp-crypto.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/ccp.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/ccree.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/cdrom.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/cfb.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/chacha20_generic.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/chacha20-x86_64.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/chacha20poly1305.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/chcr.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/chtls.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/cmac.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/crc-itu-t.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/crc16.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/crc32_generic.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/crc32-pclmul.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/crc32c_generic.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/crc32c-intel.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/crct10dif-pclmul.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/cryptd.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/crypto_engine.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/crypto_simd.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/crypto_user.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/cts.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/cxgb4.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/deflate.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/des_generic.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/des3_ede-x86_64.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/dm-bio-prison.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/dm-bufio.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/dm-cache-smq.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/dm-cache.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/dm-crypt.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/dm-log.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/dm-mirror.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/dm-mod.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/dm-persistent-data.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/dm-region-hash.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/dm-snapshot.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/dm-thin-pool.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/ecdh_generic.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/echainiv.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/ehci-hcd.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/ehci-pci.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/ext4.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/fcrypt.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/firewire-core.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/firewire-ohci.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/firewire-sbp2.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/fscrypto.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/ghash-clmulni-intel.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/glue_helper.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/hid-generic.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/hid.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/intel_qat.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/jbd2.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/keywrap.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/khazad.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/libahci.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/libata.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/libcrc32c.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/lrw.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/lz4_compress.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/lz4.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/lz4hc_compress.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/lz4hc.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/mbcache.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/mcryptd.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/md4.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/michael_mic.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/morus1280_glue.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/morus1280-avx2.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/morus1280-sse2.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/morus1280.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/morus640_glue.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/morus640-sse2.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/morus640.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/n5pf.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/padlock-aes.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/padlock-sha.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/pata_acpi.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/pata_jmicron.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/pcbc.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/pcrypt.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/poly1305_generic.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/poly1305-x86_64.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/qat_c3xxx.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/qat_c3xxxvf.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/qat_c62x.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/qat_c62xvf.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/qat_dh895xcc.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/qat_dh895xccvf.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/raid6_pq.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/rmd128.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/rmd160.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/rmd256.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/rmd320.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/rng-core.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/salsa20_generic.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/scsi_mod.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/sd_mod.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/seed.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/serpent_generic.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/serpent-avx-x86_64.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/serpent-avx2.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/serpent-sse2-x86_64.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/sha1-mb.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/sha1-ssse3.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/sha256-mb.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/sha256-ssse3.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/sha3_generic.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/sha512_generic.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/sha512-mb.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/sha512-ssse3.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/sm3_generic.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/sm4_generic.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/speck.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/sr_mod.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/tcrypt.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/tea.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/tgr192.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/tls.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/twofish_common.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/twofish_generic.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/twofish-avx-x86_64.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/twofish-x86_64-3way.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/twofish-x86_64.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/uhci-hcd.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/usb-common.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/usb-storage.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/usbcore.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/usbhid.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/virtio_crypto.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/virtio_ring.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/virtio.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/vmac.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/wp512.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/xcbc.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/xhci-hcd.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/xhci-pci.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/xor.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/xts.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/xxhash.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/zstd_compress.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/zstd_decompress.ko usr/lib/modules/4.18.3-arch1-1-ARCH/kernel/zstd.ko usr/lib/modules/4.18.3-arch1-1-ARCH/modules.alias.bin usr/lib/modules/4.18.3-arch1-1-ARCH/modules.builtin.bin usr/lib/modules/4.18.3-arch1-1-ARCH/modules.dep.bin usr/lib/modules/4.18.3-arch1-1-ARCH/modules.devname usr/lib/modules/4.18.3-arch1-1-ARCH/modules.softdep usr/lib/modules/4.18.3-arch1-1-ARCH/modules.symbols.bin

As far as I can tell, all the twenty modules above are included in the default initramfs.

By the way, my hooks in /etc/mkinitcpio.conf are

base udev autodetect keyboard keymap modconf block encrypt lvm2 filesystems fsck

Finally, I was able to boot with the default initramfs using the kernel parameters "nosmp", "maxcpus=0" (equivalent to "nosmp") and "maxcpus=1", but not with "maxcpus=2", which I believe is the maximum for my system. Looking at the hardware from the users in this thread, I have the impression that the problem seems to occur with old Intel Core 2 Duo and related CPUs (I have a Core 2 Duo E8400). Therefore I looked for related changes in the kernel version 4.18 and I found out that there were at least these changes regarding the boot process on x86:

https://git.kernel.org/pub/scm/linux/ke … 7578ec1a71