Public bug reported: Regression in Ubuntu 24.04 Noble lowlatency kernel affecting the Fintek F81604 USB CAN driver.
Confirmed kernel versions: GOOD: 6.8.0-134-lowlatency BAD: 6.8.0-136-lowlatency 6.8.0-138-lowlatency On the affected kernels CAN RX still works, but CAN TX does not complete. Minimal reproduction: sudo ip link set can1 down sudo ip link set can1 type can bitrate 125000 restart-ms 50 sudo ip link set can1 up cansend can1 123#11223344 cansend() returns successfully, but: - nothing appears in candump on a separate socket - the CAN TX packet counter remains at 0 - the kernel continuously logs: f81604_read_int_callback: short int URB: 9 < 12 The same hardware and configuration work correctly when booted with 6.8.0-134-lowlatency. Root cause has been identified upstream. The regression was introduced by: 7299b1b39a255f6092ce4ec0b65f66e9d6a357af can: usb: f81604: handle short interrupt urb messages properly The F81604 interrupt payload contains 9 bytes. struct f81604_int_data was declared __packed __aligned(4), making sizeof(struct f81604_int_data) equal to 12 because of tail padding. The new short-URB validation compares urb->actual_length against this padded sizeof(), so the valid 9-byte hardware interrupt is rejected. This prevents the TX-complete interrupt from being processed. An upstream fix has already been accepted into the linux-can maintainer tree: cfc9bc6e7d37c5a085397bb98839dfa993c92ab8 can: usb: f81604: fix struct f81604_int_data size mismatch It is currently in linux-can/testing and was included in: linux-can-fixes-for-7.3-20260826 The upstream commit contains: Fixes: 7299b1b39a25 Cc: [email protected] This regression completely prevents CAN transmission on affected F81604 hardware. I have access to the affected hardware and can promptly test/verify a Noble kernel build containing the upstream fix. ProblemType: Bug DistroRelease: Ubuntu 24.04 Package: linux-image-6.8.0-138-lowlatency 6.8.0-138.138.1 ProcVersionSignature: Ubuntu 6.8.0-138.138.1-lowlatency 6.8.12 Uname: Linux 6.8.0-138-lowlatency x86_64 AlsaVersion: Advanced Linux Sound Architecture Driver Version k6.8.0-138-lowlatency. AplayDevices: Error: [Errno 2] No such file or directory: 'aplay' ApportVersion: 2.28.3-0ubuntu0.1 Architecture: amd64 ArecordDevices: Error: [Errno 2] No such file or directory: 'arecord' AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/by-path', '/dev/snd/controlC0', '/dev/snd/hwC0D2', '/dev/snd/pcmC0D8p', '/dev/snd/pcmC0D7p', '/dev/snd/pcmC0D3p', '/dev/snd/seq', '/dev/snd/timer'] failed with exit code 1: CRDA: N/A Card0.Amixer.info: Error: [Errno 2] No such file or directory: 'amixer' Card0.Amixer.values: Error: [Errno 2] No such file or directory: 'amixer' CasperMD5CheckResult: unknown Date: Wed Aug 26 13:36:30 2026 IwConfig: Error: [Errno 2] No such file or directory: 'iwconfig' Lspci: Error: [Errno 2] No such file or directory: 'lspci' Lspci-vt: Error: [Errno 2] No such file or directory: 'lspci' Lsusb: Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub Bus 001 Device 002: ID 2c42:1709 FINTEK USB TO CANBUS BRIDGE Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub Lsusb-t: /: Bus 001.Port 001: Dev 001, Class=root_hub, Driver=xhci_hcd/8p, 480M |__ Port 001: Dev 002, If 0, Class=[unknown], Driver=f81604, 12M /: Bus 002.Port 001: Dev 001, Class=root_hub, Driver=xhci_hcd/7p, 5000M MachineType: Advantech UNO-137-E1 PciMultimedia: ProcEnviron: LANG=en_US.UTF-8 PATH=(custom, no user) SHELL=/bin/bash TERM=xterm-256color ProcFB: ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-6.8.0-138-lowlatency root=UUID=28bbc38e-b09f-4cfc-9c45-42acc99392b5 ro pcie_aspm=off intel_idle.max_cstate=1 quiet splash vt.handoff=7 RelatedPackageVersions: linux-restricted-modules-6.8.0-138-lowlatency N/A linux-backports-modules-6.8.0-138-lowlatency N/A linux-firmware 20240318.git3b128b60-0ubuntu2.29 RfKill: Error: [Errno 2] No such file or directory: 'rfkill' SourcePackage: linux-lowlatency UpgradeStatus: No upgrade log present (probably fresh install) dmi.bios.date: 10/06/2021 dmi.bios.release: 5.12 dmi.bios.vendor: American Megatrends Inc. dmi.bios.version: 112 dmi.board.asset.tag: Default string dmi.board.name: UNO-137-E1 dmi.board.vendor: Advantech dmi.board.version: F1.12 dmi.chassis.asset.tag: Default string dmi.chassis.type: 3 dmi.chassis.vendor: Default string dmi.chassis.version: Default string dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr112:bd10/06/2021:br5.12:svnAdvantech:pnUNO-137-E1:pvrF1.12:rvnAdvantech:rnUNO-137-E1:rvrF1.12:cvnDefaultstring:ct3:cvrDefaultstring:skuDefaultstring: dmi.product.family: Default string dmi.product.name: UNO-137-E1 dmi.product.sku: Default string dmi.product.version: F1.12 dmi.sys.vendor: Advantech ** Affects: linux-lowlatency (Ubuntu) Importance: Undecided Status: New ** Tags: amd64 apport-bug noble -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/2165144 Title: [REGRESSION] f81604 CAN TX broken since 6.8.0-136 due to interrupt data struct padding To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux-lowlatency/+bug/2165144/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
