5.13-rt1 + KVM = WARNING: at fs/eventfd.c:74 eventfd_signal()

[Daniel Bristot de Oliveira]

Hey

I use kvm-vm for regular development, and while using the kernel-rt v5.13-rt1
(the latest) on the host, and a regular kernel on the guest, after a while,
this happens:

[ 1723.404979] ------------[ cut here ]------------
[ 1723.404981] WARNING: CPU: 12 PID: 2554 at fs/eventfd.c:74 eventfd_signal+0x7e/0x90
[ 1723.404989] Modules linked in: vhost_net vhost vhost_iotlb tap tun rfcomm snd_seq_dummy snd_hrtimer xt_CHECKSUM xt_MASQUERADE xt_conntrack ipt_REJECT nf_nat_tftp nf_conntrack_tftp bridge stp llc ccm nft_objref nf_conntrack_netbios_ns nf_conntrack_broadcast nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nft_chain_nat ip6table_nat ip6table_mangle ip6table_raw ip6table_security iptable_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 iptable_mangle iptable_raw iptable_security ip_set nf_tables nfnetlink ip6table_filter ip6_tables iptable_filter cmac bnep intel_rapl_msr sunrpc intel_rapl_common kvm_amd kvm ath10k_pci snd_hda_codec_realtek ath10k_core snd_hda_codec_generic ledtrig_audio snd_hda_codec_hdmi snd_hda_intel snd_intel_dspcfg snd_hda_codec ath btusb mac80211 snd_hwdep btrtl snd_hda_core btbcm snd_seq irqbypass rapl vfat snd_seq_device btintel dell_wmi_descriptor alienware_wmi wmi_bmof libarc4 fat pcspkr snd_pcm
[ 1723.405033]  bluetooth joydev k10temp i2c_piix4 cfg80211 snd_timer snd soundcore ecdh_generic ecc rfkill gpio_amdpt gpio_generic acpi_cpufreq zram ip_tables nouveau hid_logitech_hidpp video drm_ttm_helper ttm i2c_algo_bit mxm_wmi drm_kms_helper crct10dif_pclmul crc32_pclmul crc32c_intel cec drm ghash_clmulni_intel r8169 nvme hid_logitech_dj ccp nvme_core sp5100_tco wmi fuse
[ 1723.405051] CPU: 12 PID: 2554 Comm: vhost-2529 Not tainted 5.13.0-rt-rt1+ #2
[ 1723.405054] Hardware name: Alienware Alienware Aurora Ryzen Edition/0TYR0X, BIOS 2.1.2 02/25/2021
[ 1723.405055] RIP: 0010:eventfd_signal+0x7e/0x90
[ 1723.405059] Code: 01 00 00 00 be 03 00 00 00 4c 89 ef e8 5b ec d9 ff 65 ff 0d e4 34 c9 5a 4c 89 ef e8 ec a8 86 00 4c 89 e0 5b 5d 41 5c 41 5d c3 <0f> 0b 45 31 e4 5b 5d 4c 89 e0 41 5c 41 5d c3 0f 1f 00 0f 1f 44 00
[ 1723.405060] RSP: 0018:ffffb719c2f67d70 EFLAGS: 00010202
[ 1723.405062] RAX: 0000000000000001 RBX: ffff9f4897364ae0 RCX: 0000000000000000
[ 1723.405063] RDX: 0000000000000791 RSI: 0000000000000001 RDI: ffff9f489ae647e0
[ 1723.405064] RBP: 0000000000000100 R08: 0000000000000000 R09: 0000000000000001
[ 1723.405065] R10: 000000000004715e R11: 00000000000036e0 R12: 0000000000000001
[ 1723.405066] R13: ffff9f489b7643c0 R14: ffffb719c2f67e20 R15: ffff9f4897364ae0
[ 1723.405067] FS:  0000000000000000(0000) GS:ffff9f4f9ed00000(0000) knlGS:0000000000000000
[ 1723.405068] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1723.405069] CR2: 00007ffa78355000 CR3: 0000000114b7c000 CR4: 0000000000750ee0
[ 1723.405071] PKRU: 55555554
[ 1723.405071] Call Trace:
[ 1723.405078]  vhost_tx_batch.constprop.0+0x7d/0xc0 [vhost_net]
[ 1723.405083]  handle_tx_copy+0x15b/0x5c0 [vhost_net]
[ 1723.405088]  ? __vhost_add_used_n+0x200/0x200 [vhost]
[ 1723.405092]  handle_tx+0xa5/0xe0 [vhost_net]
[ 1723.405095]  vhost_worker+0x93/0xd0 [vhost]
[ 1723.405099]  kthread+0x186/0x1a0
[ 1723.405103]  ? __kthread_parkme+0xa0/0xa0
[ 1723.405105]  ret_from_fork+0x22/0x30
[ 1723.405110] ---[ end trace 0000000000000002 ]---

and my communication with the VM dies. Rebooting the VM makes it work again.

-- Daniel