Deadlock on process exit

[mbyzhang]

A deadlock can possibly occur when the multiple forked child process races to exit.

[  968.164661] watchdog: BUG: soft lockup - CPU#2 stuck for 302s! [forktest:5154]
[  968.164664] Modules linked in: fault_page_tracker(OE) snd_hda_codec_hdmi snd_ctl_led snd_hda_codec_realtek snd_sof_pci_intel_tgl snd_hda_codec_generic snd_sof_intel_hda_common soundwire_intel intel_tcc_cooling soundwire_generic_allocation soundwire_cadence snd_sof_intel_hda snd_sof_pci x86_pkg_temp_thermal snd_sof_xtensa_dsp intel_powerclamp snd_sof snd_sof_utils snd_soc_hdac_hda snd_hda_ext_core snd_soc_acpi_intel_match snd_soc_acpi soundwire_bus snd_soc_core snd_compress ac97_bus snd_pcm_dmaengine coretemp snd_hda_intel snd_intel_dspcfg snd_intel_sdw_acpi snd_hda_codec snd_hda_core kvm_intel mei_hdcp mei_pxp binfmt_misc intel_rapl_msr i915 kvm snd_hwdep crct10dif_pclmul polyval_clmulni snd_pcm polyval_generic ghash_clmulni_intel snd_seq_midi drm_buddy aesni_intel snd_seq_midi_event ttm dell_wmi ledtrig_audio crypto_simd snd_rawmidi nls_iso8859_1 drm_display_helper cryptd cec rapl rc_core intel_cstate snd_seq drm_kms_helper snd_seq_device dell_smbios snd_timer
[  968.164695]  processor_thermal_device_pci cmdlinepart i2c_algo_bit snd dcdbas dell_wmi_sysman processor_thermal_device spi_nor processor_thermal_rfim fb_sys_fops processor_thermal_mbox dell_wmi_descriptor firmware_attributes_class mtd processor_thermal_rapl wmi_bmof mei_me syscopyarea soundcore intel_rapl_common sysfillrect sysimgblt mei int340x_thermal_zone mac_hid acpi_tad intel_hid int3400_thermal acpi_thermal_rel sparse_keymap acpi_pad sch_fq_codel nfsd msr auth_rpcgss parport_pc nfs_acl ppdev lockd lp grace parport drm sunrpc efi_pstore ip_tables x_tables autofs4 mlx4_ib ib_uverbs mlx4_en ib_core crc32_pclmul ahci spi_intel_pci nvme libahci intel_lpss_pci i2c_i801 e1000e intel_lpss xhci_pci spi_intel nvme_core i2c_smbus idma64 xhci_pci_renesas mlx4_core ucsi_acpi nvme_common typec_ucsi typec wmi video pinctrl_alderlake
[  968.164751] CPU: 2 PID: 5154 Comm: forktest Tainted: G    B D W  OEL     6.0.6-odf+ #2
[  968.164754] Hardware name: Dell Inc. OptiPlex 7000/0FG47G, BIOS 1.15.0 07/12/2023
[  968.164756] RIP: 0010:native_queued_spin_lock_slowpath+0x7f/0x300
[  968.164760] Code: 24 08 0f 92 c2 41 8b 04 24 0f b6 d2 c1 e2 08 30 e4 09 d0 a9 00 01 ff ff 0f 85 f4 01 00 00 85 c0 74 12 41 8b 04 24 84 c0 74 0a <f3> 90 41 8b 04 24 84 c0 75 f6 b8 01 00 00 00 66 41 89 04 24 5b 41
[  968.164765] RSP: 0018:ffffa1ffc047f8a8 EFLAGS: 00000202
[  968.164767] RAX: 0000000000000101 RBX: 00007ffff7c00000 RCX: 000ffffffffff000
[  968.164770] RDX: 0000000000000000 RSI: 0000000000000000 RDI: fffff3210d88a1e8
[  968.164772] RBP: ffffa1ffc047f8d0 R08: 00007ffff7e00000 R09: 0000000000000000
[  968.164774] R10: ffff8e7d8f8b76d8 R11: ffffffffffffffff R12: fffff3210d88a1e8
[  968.164777] R13: fffff3210d88a1e8 R14: 00007ffff7c00000 R15: ffff8e760a723898
[  968.164779] FS:  0000000000000000(0000) GS:ffff8e7d8f880000(0000) knlGS:0000000000000000
[  968.164782] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  968.164784] CR2: 00007ffff000c008 CR3: 000000088e210006 CR4: 0000000000770ee4
[  968.164787] DR0: 0000555555555291 DR1: 0000000000000000 DR2: 0000000000000000
[  968.164790] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
[  968.164792] PKRU: 55555554
[  968.164793] Call Trace:
[  968.164795]  <TASK>
[  968.164796]  _raw_spin_lock+0x29/0x30
[  968.164799]  multiple_cow_pte_rss+0x14a/0x3e0
[  968.164803]  handle_cow_pte+0x575/0x600
[  968.164806]  ? __mod_lruvec_state+0x37/0x50
[  968.164810]  ? folio_memcg_unlock+0x38/0x70
[  968.164812]  ? unlock_page_memcg+0x18/0x50
[  968.164815]  unmap_page_range+0x5d3/0x1370
[  968.164818]  ? select_task_rq_fair+0x19f/0x1e80
[  968.164822]  unmap_single_vma+0x87/0x110
[  968.164825]  unmap_vmas+0x90/0x110
[  968.164828]  exit_mmap+0xab/0x1d0
[  968.164833]  __mmput+0x48/0x130
[  968.164835]  mmput+0x2d/0x40
[  968.164838]  do_exit+0x2d8/0xa90
[  968.164842]  do_group_exit+0x35/0xa0
[  968.164845]  get_signal+0xa1e/0xa40
[  968.164849]  arch_do_signal_or_restart+0x37/0x7b0
[  968.164852]  ? ptrace_do_notify+0x9e/0xd0
[  968.164855]  exit_to_user_mode_prepare+0x101/0x170
[  968.164859]  syscall_exit_to_user_mode+0x26/0x50
[  968.164862]  do_syscall_64+0x69/0x90
[  968.164865]  ? switch_fpu_return+0x4e/0xe0
[  968.164868]  ? exit_to_user_mode_prepare+0x8b/0x170
[  968.164872]  ? syscall_exit_to_user_mode+0x26/0x50
[  968.164874]  entry_SYSCALL_64_after_hwframe+0x63/0xcd
[  968.164877] RIP: 0033:0x555555555291
[  968.164879] Code: Unable to access opcode bytes at RIP 0x555555555267.
[  968.164880] RSP: 002b:00007fffffffe390 EFLAGS: 00000206
[  968.164882] RAX: 00007ffef8b0e010 RBX: 0000000000003331 RCX: 0000000000000001
[  968.164884] RDX: 0000000000000000 RSI: 00005555555592a0 RDI: 00007fffffffde20
[  968.164886] RBP: 00007ffef9bff010 R08: 0000000000000000 R09: 0000000000000000
[  968.164888] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000284
[  968.164890] R13: 00000000138a06b5 R14: 00007ffef7bff010 R15: 00007fffffffe3b0
[  968.164893]  </TASK>