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It is repeated 5 times. Config: Debian Trixie with xfce4 Desktop libevl: r56 linux-evl: v6.12.67-evl2-rebase I traced the issue already trough the following code: net/core/net_namespace.c:355 kernel/evl/net/net.c:35 kernel/evl/net/ipv4/ipv4.c:41 kernel/evl/net/ipv4/arp.c:323 However, I lack the knowledge to do a proper fix. One way would be to just check in evl_net_init_arp() if it is already registered and don't do it more than once but that doesn't feel right. Some background: I am working on integrating Xenomai3/4 into LinuxCNC. Due to this, I have a full desktop running with a Xenomai kernel. Probably one of the installed applications triggers this issue. It is just a hobby and I am not an official maintainer of LinuxCNC but if it works well, it might get merged. Regards Hannes Full warning, one of 5 but they are all equal: [ 4.158674] ------------[ cut here ]------------ [ 4.158680] notifier callback netevent_handler already registered [ 4.158716] WARNING: CPU: 15 PID: 1095 at kernel/notifier.c:31 notifier_chain_register+0x3e/0xb0 [ 4.158736] Modules linked in: binfmt_misc intel_rapl_msr intel_rapl_common ccp kvm irqbypass crct10dif_pclmul ghash_clmulni_intel snd_hda_codec_generic sha512_ssse3 sha256_ssse3 sha1_ssse3 snd_hda_intel aesni_intel snd_intel_dspcfg snd_intel_sdw_acpi gf128mul snd_hda_codec crypto_simd cryptd pcspkr snd_hda_core snd_hwdep snd_pcm snd_timer snd soundcore evdev sg parport_pc ppdev lp parport efi_pstore configfs nfnetlink vsock_loopback vmw_vsock_virtio_transport_common vmw_vsock_vmci_transport vsock vmw_vmci qemu_fw_cfg virtio_rng ip_tables x_tables autofs4 ext4 crc32c_generic crc16 mbcache jbd2 virtio_gpu virtio_dma_buf drm_shmem_helper sr_mod drm_kms_helper cdrom iTCO_wdt intel_pmc_bxt xhci_pci iTCO_vendor_support watchdog xhci_hcd ahci libahci drm crc32_pclmul usbcore crc32c_intel virtio_blk libata psmouse virtio_net net_failover serio_raw failover usb_common scsi_mod i2c_i801 lpc_ich i2c_smbus scsi_common button [ 4.158773] CPU: 15 UID: 0 PID: 1095 Comm: (crub_all) Not tainted 6.12.67-xenomai4-53a3aa #3 [ 4.158777] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 [ 4.158778] IRQ stage: Linux [ 4.158781] RIP: 0010:notifier_chain_register+0x3e/0xb0 [ 4.158784] Code: 10 7f 33 75 04 84 d2 75 7d 48 8d 78 08 48 8b 40 08 48 85 c0 74 20 48 39 c6 75 e0 48 8b 36 48 c7 c7 98 e1 54 9f e8 b2 28 fc ff <0f> 0b b8 ef ff ff ff c3 cc cc cc cc 48 89 46 08 48 89 37 66 90 31 [ 4.158785] RSP: 0018:ffffc91b414e7d00 EFLAGS: 00010282 [ 4.158789] RAX: 0000000000000000 RBX: ffffffffa090b240 RCX: 0000000000000027 [ 4.158793] RDX: ffff8901efda0948 RSI: 0000000000000001 RDI: ffff8901efda0940 [ 4.158794] RBP: ffffffff9fe809c0 R08: 0000000000000a74 R09: 0000000000000000 [ 4.158794] R10: 0000000000000001 R11: 0000000000000000 R12: ffffffff9fc5a3e0 [ 4.158795] R13: 0000000000000000 R14: ffffffff9fc528ec R15: ffffc91b414e7d58 [ 4.158797] FS: 00007f16c63765c0(0000) GS:ffff8901efd80000(0000) knlGS:0000000000000000 [ 4.158801] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 4.158802] CR2: 00007f16c719f160 CR3: 000000010491c000 CR4: 0000000000750ef0 [ 4.158803] PKRU: 55555554 [ 4.158803] Call Trace: [ 4.158815] [ 4.158816] atomic_notifier_chain_register+0x24/0x40 [ 4.158820] evl_net_init_arp+0x3f/0x50 [ 4.158830] evl_net_init_ipv4+0x2a/0x100 [ 4.158833] setup_net+0x9e/0x2b0 [ 4.158858] copy_net_ns+0x111/0x270 [ 4.158861] create_new_namespaces+0x113/0x2e0 [ 4.158865] unshare_nsproxy_namespaces+0x58/0xa0 [ 4.158868] ksys_unshare+0x17d/0x400 [ 4.158887] __x64_sys_unshare+0x12/0x20 [ 4.158890] do_syscall_64+0xc0/0x230 [ 4.158913] ? syscall_exit_to_user_mode+0x1da/0x1f0 [ 4.158916] ? do_syscall_64+0xcc/0x230 [ 4.158917] ? do_user_addr_fault+0x4c1/0x750 [ 4.158926] ? __ct_user_enter+0x29/0xd0 [ 4.158927] entry_SYSCALL_64_after_hwframe+0x76/0x7e [ 4.158949] RIP: 0033:0x7f16c6ebe967 [ 4.158960] Code: 73 01 c3 48 8b 0d a9 34 0d 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 10 01 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 79 34 0d 00 f7 d8 64 89 01 48 [ 4.158961] RSP: 002b:00007ffe188cc308 EFLAGS: 00000246 ORIG_RAX: 0000000000000110 [ 4.158962] RAX: ffffffffffffffda RBX: 00007ffe188cc8c8 RCX: 00007f16c6ebe967 [ 4.158962] RDX: 0000000000000000 RSI: 00007ffe188cc270 RDI: 0000000040000000 [ 4.158963] RBP: 00007ffe188cc350 R08: 0000000000000000 R09: 0000000000000000 [ 4.158963] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000040000000 [ 4.158967] R13: 00000000fffffff5 R14: 00007f16c7374380 R15: 00000000fffffff5 [ 4.158969] [ 4.158969] ---[ end trace 0000000000000000 ]---