{"id":20488,"date":"2026-04-20T14:52:54","date_gmt":"2026-04-20T14:52:54","guid":{"rendered":"http:\/\/www.trueangle.org\/?p=20488"},"modified":"2026-04-28T15:35:21","modified_gmt":"2026-04-28T15:35:21","slug":"hung_task_all_cpu_backtrace","status":"publish","type":"post","link":"https:\/\/www.trueangle.org\/index.php\/2026\/04\/20\/hung_task_all_cpu_backtrace\/","title":{"rendered":"hung_task_all_cpu_backtrace( topic related to CPUs dumping their backtraces )"},"content":{"rendered":"

ABOUT <\/p>\n

\r\n
hung_task_all_cpu_backtrace<\/p>\r\n\r\nIf this option is set, the kernel will send an NMI to all CPUs to dump their backtraces when a hung task\r\nis detected. This file shows up if CONFIG_DETECT_HUNG_TASK and CONFIG_SMP are enabled.\r\n\r\n0: Won\u2019t show all CPUs backtraces when a hung task is detected. This is the default behavior\r\n1: Will non-maskably interrupt all CPUs and dump their backtraces when a hung task is detected.\r\n<\/pre>\n
\nLINUX KERNEL RELATED PARAMETER\n<\/p>\n

\n$cat \/proc\/sys\/kernel\/hung_task_all_cpu_backtrace
\n0
\n$echo 1 | sudo tee \u2013append \/proc\/sys\/kernel\/hung_task_all_cpu_backtrace
\n[sudo] password for jeffrin:
\n1
\n$cat \/proc\/sys\/kernel\/hung_task_all_cpu_backtrace
\n1
\n$
\n<\/code><\/p>\n
\nPARAMETER RELATED\n<\/p>\n
USERSPACE PROCESS BACKTRACE
\n
\n (gdb) bt
\n#0  __syscall_cancel_arch () at ..\/sysdeps\/unix\/sysv\/linux\/x86_64\/syscall_cancel.S:56
\n#1  0x00007ffff64197a4 in __internal_syscall_cancel
\n    (a1=, a2=, a3=, a4=, a5=a5@entry=8, a6=a6@entry=0, nr=271) at .\/nptl\/cancellation.c:49
\n#2  0x00007ffff64197ed in __syscall_cancel
\n    (a1=, a2=, a3=, a4=, a5=a5@entry=8, a6=a6@entry=0, nr=271) at .\/nptl\/cancellation.c:75
\n#3  0x00007ffff648f29e in __GI_ppoll
\n    (fds=, nfds=, timeout=, sigmask=) at ..\/sysdeps\/unix\/sysv\/linux\/ppoll.c:42
\n#4  0x00007ffff7951b34 in ??? () at \/usr\/lib\/x86_64-linux-gnu\/libglib-2.0.so.0
\n#5  0x00007ffff7952210 in g_main_context_iteration ()
\n    at \/usr\/lib\/x86_64-linux-gnu\/libglib-2.0.so.0
\n#6  0x00007ffff76fe13d in g_application_run ()
\n    at \/usr\/lib\/x86_64-linux-gnu\/libgio-2.0.so.0
\n#7  0x000055555580dfad in app_run ()
\n#8  0x0000555555641f3b in main ()
\n(gdb) <\/p>\n
<\/code><\/p>\n
\nBACKTRACE FROM KERNEL RING BUFFER\n<\/p>\n

\necho 1 | sudo tee \/proc\/sys\/kernel\/sysrq<\/p>\n
echo l | sudo tee \/proc\/sysrq-trigger.<\/p>\n
dmesg <\/p>\n
KERNEL SPACE BACKTRACE<\/p>\n
[30208.196481] sysrq: Show backtrace of all active CPUs
\n[30208.196491] NMI backtrace for cpu 0
\n[30208.196494] CPU: 0 UID: 0 PID: 45306 Comm: tee Not tainted 6.18.20-rc1+ #61 PREEMPT(lazy)
\n[30208.196498] Hardware name: HP HP Laptop 15s-ey1xxx\/8706, BIOS F.61 03\/25\/2022
\n[30208.196500] Call Trace:
\n[30208.196503]  <TASK>code
\n[30208.196507]  dump_stack_lvl+0x5d\/0x80
\n[30208.196514]  nmi_cpu_backtrace.cold+0x18\/0x65
\n[30208.196518]  ? __pfx_nmi_raise_cpu_backtrace+0x10\/0x10
\n[30208.196524]  nmi_trigger_cpumask_backtrace+0xf4\/0x110
\n[30208.196529]  __handle_sysrq.cold+0x8a\/0x160
\n[30208.196534]  write_sysrq_trigger+0x59\/0xa0
\n[30208.196540]  proc_reg_write+0x5a\/0xb0
\n[30208.196544]  vfs_write+0xce\/0x480
\n[30208.196552]  ksys_write+0x73\/0xf0
\n[30208.196556]  do_syscall_64+0x81\/0x7f0
\n[30208.196562]  ? srso_return_thunk+0x5\/0x5f
\n[30208.196565]  ? __x64_sys_openat+0x61\/0xa0
\n[30208.196569]  ? srso_return_thunk+0x5\/0x5f
\n[30208.196571]  ? do_syscall_64+0xb9\/0x7f0
\n[30208.196576]  ? srso_return_thunk+0x5\/0x5f
\n[30208.196579]  ? ksys_fadvise64_64+0x6c\/0xa0
\n[30208.196584]  ? srso_return_thunk+0x5\/0x5f
\n[30208.196587]  ? srso_return_thunk+0x5\/0x5f
\n[30208.196589]  ? do_syscall_64+0xb9\/0x7f0
\n[30208.196593]  ? srso_return_thunk+0x5\/0x5f
\n[30208.196597]  ? do_user_addr_fault+0x21a\/0x690
\n[30208.196602]  ? srso_return_thunk+0x5\/0x5f
\n[30208.196605]  ? srso_return_thunk+0x5\/0x5f
\n[30208.196609]  entry_SYSCALL_64_after_hwframe+0x76\/0x7e
\n[30208.196613] RIP: 0033:0x7f8875a3a7d2
\n[30208.196638] Code: 18 41 8b 93 08 03 00 00 59 5e 48 83 f8 fc 75 1a 83 e2 39 83 fa 08 75 12 e8 2b ff ff ff 0f 1f 00 49 89 ca 48 8b 44 24 20 0f 05 <48> 83 c4 18 c3 66 0f 1f 84 00 00 00 00 00 48 83 ec 10 ff 74 24 18
\n[30208.196640] RSP: 002b:00007fffda92a5b0 EFLAGS: 00000202 ORIG_RAX: 0000000000000001
\n[30208.196644] RAX: ffffffffffffffda RBX: 000055b4a7c9c310 RCX: 00007f8875a3a7d2
\n[30208.196645] RDX: 0000000000000002 RSI: 00007fffda92a750 RDI: 0000000000000003
\n[30208.196647] RBP: 0000000000000002 R08: 0000000000000000 R09: 0000000000000000
\n[30208.196649] R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000002
\n[30208.196650] R13: 00007fffda92a750 R14: 00007fffda92a750 R15: 0000000000000002
\n[30208.196659]  <\/TASK>
\n[30208.196688] Sending NMI from CPU 0 to CPUs 1-3:
\n[30208.196697] NMI backtrace for cpu 1
\n[30208.196699] CPU: 1 UID: 0 PID: 345 Comm: systemd-journal Not tainted 6.18.20-rc1+ #61 PREEMPT(lazy)
\n[30208.196702] Hardware name: HP HP Laptop 15s-ey1xxx\/8706, BIOS F.61 03\/25\/2022
\n[30208.196703] RIP: 0033:0x7f51c5e71490
\n[30208.196710] Code: bd fd ff ff b8 f4 ff ff ff e9 40 fd ff ff 31 d2 e9 4c ff ff ff 89 da e9 45 ff ff ff e8 f9 8c e4 ff e8 f4 fb ff ff 0f 1f 40 00  0f 1e fa 41 54 49 89 d4 55 48 89 cd 53 48 89 fb e8 1a 91 ff ff
\n[30208.196712] RSP: 002b:00007ffc7ed4ca08 EFLAGS: 00000246
\n[30208.196714] RAX: 0000000000000000 RBX: 000056303827baf0 RCX: 0000000000000000
\n[30208.196716] RDX: 00007ffc7ed4ca18 RSI: 00007ffc7ed4ca20 RDI: 0000000000000000
\n[30208.196717] RBP: 00007ffc7ed4ca20 R08: 00007f51c62b3070 R09: 0000000000000000
\n[30208.196718] R10: 00007f51c62b3000 R11: 0000000000c1eb8a R12: 000056303827baf0
\n[30208.196720] R13: 0000000000000000 R14: ffffffffffffffff R15: 000056302ba21658
\n[30208.196721] FS:  00007f51c6172840 GS:  0000000000000000
\n[30208.196723] NMI backtrace for cpu 2 skipped: idling at io_idle+0x3\/0x30
\n[30208.196736] NMI backtrace for cpu 3
\n[30208.196741] CPU: 3 UID: 0 PID: 806 Comm: in:imklog Not tainted 6.18.20-rc1+ #61 PREEMPT(lazy)
\n[30208.196749] Hardware name: HP HP Laptop 15s-ey1xxx\/8706, BIOS F.61 03\/25\/2022
\n[30208.196752] RIP: 0010:vsnprintf+0x355\/0x5e0
\n[30208.196761] Code: 0a 0f b6 03 49 89 df eb 27 4c 89 e0 48 8b 7c 24 30 48 8b 4c 24 20 4c 29 f8 4c 63 c0 48 39 cf 0f 82 cb 00 00 00 4c 01 44 24 30 <0f> b6 03 49 89 df 84 c0 0f 85 29 fd ff ff e9 09 fe ff ff 48 8b 44
\n[30208.196765] RSP: 0018:ffffd0d14ce93878 EFLAGS: 00000286
\n[30208.196771] RAX: ffffd0d14ce93992 RBX: ffffffff9358ebf2 RCX: 000000000000003e
\n[30208.196775] RDX: 0000000000000000 RSI: ffffffff9358ebf1 RDI: ffffd0d14ce93992
\n[30208.196779] RBP: ffffd0d14ce938e8 R08: 0000000000000001 R09: 00000000ffffffff
\n[30208.196782] R10: 0000000000000000 R11: 0000000000000004 R12: ffffffff9358ebf2
\n[30208.196785] R13: 0000000000000400 R14: 0000000000000400 R15: ffffffff9358ebf1
\n[30208.196789] FS:  00007f2e35a6b6c0(0000) GS:ffff8f48445af000(0000) knlGS:0000000000000000
\n[30208.196794] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
\n[30208.196798] CR2: 000055b82387b970 CR3: 000000010a0e0000 CR4: 00000000003506f0
\n[30208.196802] Call Trace:
\n[30208.196805]  <TASK>
\n[30208.196818]  sprintf+0x5f\/0x80
\n[30208.196828]  ? srso_return_thunk+0x5\/0x5f
\n[30208.196837]  info_print_prefix+0x57\/0xe0
\n[30208.196846]  record_print_text+0x7a\/0x170
\n[30208.196860]  syslog_print+0x274\/0x360
\n[30208.196869]  ? __pfx_autoremove_wake_function+0x10\/0x10
\n[30208.196886]  do_syslog+0xd5\/0x400
\n[30208.196900]  ? srso_return_thunk+0x5\/0x5f
\n[30208.196910]  kmsg_read+0x57\/0x70
\n[30208.196918]  ? srso_return_thunk+0x5\/0x5f
\n[30208.196924]  ? __pfx_kmsg_read+0x10\/0x10
\n[30208.196930]  vfs_read+0xbf\/0x390
\n[30208.196937]  ? __seccomp_filter+0x42\/0x590
\n[30208.196953]  ksys_read+0x73\/0xf0
\n[30208.196963]  do_syscall_64+0x81\/0x7f0
\n[30208.196972]  ? srso_return_thunk+0x5\/0x5f
\n[30208.196978]  ? srso_return_thunk+0x5\/0x5f
\n[30208.196984]  ? wakeup_preempt+0x89\/0xa0
\n[30208.196992]  ? srso_return_thunk+0x5\/0x5f
\n[30208.196998]  ? ttwu_do_activate+0x86\/0x250
\n[30208.197005]  ? srso_return_thunk+0x5\/0x5f
\n[30208.197010]  ? update_rq_clock+0x81\/0x180
\n[30208.197019]  ? srso_return_thunk+0x5\/0x5f
\n[30208.197024]  ? try_to_wake_up+0x371\/0x8b0
\n[30208.197032]  ? srso_return_thunk+0x5\/0x5f
\n[30208.197037]  ? plist_del+0x5f\/0xd0
\n[30208.197046]  ? srso_return_thunk+0x5\/0x5f
\n[30208.197052]  ? wake_up_q+0x37\/0x90
\n[30208.197059]  ? srso_return_thunk+0x5\/0x5f
\n[30208.197064]  ? futex_wake+0xac\/0x1c0
\n[30208.197077]  ? srso_return_thunk+0x5\/0x5f
\n[30208.197082]  ? srso_return_thunk+0x5\/0x5f
\n[30208.197088]  ? __x64_sys_futex+0x12d\/0x210
\n[30208.197101]  ? srso_return_thunk+0x5\/0x5f
\n[30208.197106]  ? do_syscall_64+0xb9\/0x7f0
\n[30208.197114]  ? srso_return_thunk+0x5\/0x5f
\n[30208.197120]  ? switch_fpu_return+0x5b\/0xe0
\n[30208.197128]  ? srso_return_thunk+0x5\/0x5f
\n[30208.197134]  ? do_syscall_64+0x240\/0x7f0
\n[30208.197146]  ? srso_return_thunk+0x5\/0x5f
\n[30208.197151]  ? do_syscall_64+0xb9\/0x7f0
\n[30208.197158]  ? __irq_exit_rcu+0x3d\/0xe0
\n[30208.197164]  ? srso_return_thunk+0x5\/0x5f
\n[30208.197172]  entry_SYSCALL_64_after_hwframe+0x76\/0x7e
\n[30208.197177] RIP: 0033:0x7f2e35fd3ffe
\n[30208.197195] Code: 08 0f 85 15 47 ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05  90 48 83 ec 08 bf 01 00 00 00 e8 e2 eb 05 00 bf 01 00 00 00 89
\n[30208.197199] RSP: 002b:00007f2e35a4a3b8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
\n[30208.197205] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f2e35fd3ffe
\n[30208.197208] RDX: 0000000000001fa0 RSI: 00007f2e35a4ac30 RDI: 0000000000000005
\n[30208.197211] RBP: 00007f2e35a4b9c3 R08: 0000000000000000 R09: 0000000000000000
\n[30208.197214] R10: 0000000000000000 R11: 0000000000000246 R12: 000056345780d7a0
\n[30208.197217] R13: 00007f2e35a4ac30 R14: 0000000000001fa0 R15: 00007f2e35a4ac30
\n[30208.197232]  <\/TASK>
\n<\/code><\/p>\n
\nSHELL CLASS ROOM\n<\/p>\n

\n$pidof gimp
\n75203
\n$$sudo cat \/proc\/75203\/stack
\ncat: \/proc\/75203\/stack: Permission denied
\n$sudo cat \/proc\/75203\/stack
\n[sudo] password for jeffrin:
\n[<0>] poll_schedule_timeout.constprop.0+0x37\/0x90
\n[<0>] do_sys_poll+0x3fc\/0x590
\n[<0>] __x64_sys_ppoll+0xdf\/0x180
\n[<0>] do_syscall_64+0x81\/0x7f0
\n[<0>] entry_SYSCALL_64_after_hwframe+0x76\/0x7e
\n$kill -STOP 75203
\n$sudo cat \/proc\/75203\/stack
\n[<0>] do_signal_stop+0x16f\/0x200
\n[<0>] get_signal+0x230\/0x920
\n[<0>] arch_do_signal_or_restart+0x41\/0x260
\n[<0>] exit_to_user_mode_loop+0x8a\/0x130
\n[<0>] do_syscall_64+0x206\/0x7f0
\n[<0>] entry_SYSCALL_64_after_hwframe+0x76\/0x7e
\n$kill -CONT  75203
\n$sudo cat \/proc\/75203\/stack
\n[<0>] poll_schedule_timeout.constprop.0+0x37\/0x90
\n[<0>] do_sys_poll+0x3fc\/0x590
\n[<0>] __x64_sys_ppoll+0xdf\/0x180
\n[<0>] do_syscall_64+0x81\/0x7f0
\n[<0>] entry_SYSCALL_64_after_hwframe+0x76\/0x7e
\n$
\n<\/code><\/p>\n
\r\nWhat is do_signal_stop?\r\ndo_signal_stop is an internal function in the Linux kernel (specifically in kernel\/signal.c) \r\nthat handles group stops. This occurs when a process receives a signal like SIGSTOP, SIGTSTP, SIGTTIN, or \r\nSIGTTOU, which tells the process to pause execution. \r\nIts primary responsibilities include:\r\n\r\nTransitioning State: It sets the process state to TASK_STOPPED.\r\nManaging Group Stops: If one thread in a thread group initiates a stop, this function ensures\r\nthe entire group participates in the stop. Interaction with Debuggers: It handles special cases if a\r\nprocess is being traced by a debugger (like ptrace). \r\n\r\nWhy is the address all zeros?\r\nWhen you see 0000000000000000, it usually indicates that kernel pointer restriction is enabled on your system. \r\n\r\nSecurity Feature: To prevent attackers from knowing where critical functions are located in memory\r\n  (which could be used for exploits), the kernel hides the real addresses.\r\nkptr_restrict: This is controlled by the file \/proc\/sys\/kernel\/kptr_restrict. If the value\r\n is set to 1 or 2, non-privileged users will only see zeros for kernel symbols. \r\n\r\nTechnical Context\r\nThe \"t\" in the output stands for a local symbol in the text (code) section of the kernel \r\nbinary. If it were a capital \"T\", it would be a global symbol. Are you currently \r\ntroubleshooting a kernel crash or a frozen process where this function appeared in a stack trace?\r\n\r\n\r\n\r\n\r\nSOURCE: GOOGLE AI MODE\r\n<\/pre>\n
\nRELATED SOURCE CODE EXPOSURE\n<\/p>\n

\n#ifdef CONFIG_SMP
\n\t{
\n\t\t.procname\t= \"hung_task_all_cpu_backtrace\",
\n\t\t.data\t\t= &sysctl_hung_task_all_cpu_backtrace,
\n\t\t.maxlen\t\t= sizeof(int),
\n\t\t.mode\t\t= 0644,
\n\t\t.proc_handler\t= proc_dointvec_minmax,
\n\t\t.extra1\t\t= SYSCTL_ZERO,
\n\t\t.extra2\t\t= SYSCTL_ONE,
\n\t},
\n#endif \/* CONFIG_SMP *\/
\n<\/code><\/p>\n
\nRELATED FROM GOOGLE AI MODE\n<\/p>\n
\r\n\r\nThe hung_task_all_cpu_backtrace feature is not derived from a traditional academic research paper, but \r\nrather from a Linux kernel development initiative designed to improve debugging for blocked tasks (D-\r\nstate).  This mechanism was introduced to decouple panic events from CPU backtrace dumps, allowing \r\ndevelopers to see what all CPUs are doing when a hung task is detected.\r\n Key Details of hung_task_all_cpu_backtrace\r\n\r\n\r\nPurpose: To aid in debugging complex hang scenarios (e.g., deadlocks) by providing a snapshot \r\nof the entire system state, not just the stuck task.\r\n\r\nMechanism: It introduces a new sysctl (kernel.hung_task_all_cpu_backtrace) analogous to the\r\n approaches used for soft\/hard lockups.\r\n\r\nImplementation: When hung_task_warnings are still active, this feature triggers a backtrace of \r\nall CPUs upon detecting a task that has been in an uninterruptible sleep for longer than \r\nhung_task_timeout_secs.\r\n    \r\nContext: It is part of the kernel\/hung_task.c framework in the Linux kernel. \r\n\r\nRelated Research and Concepts\r\n\r\nKernel Tracing: Techniques like Ftrace and other tracers are heavily used to debug and reverse-\r\nengineer complex systems, often used to determine the execution frequency of kernel paths.\r\n    \r\nDeadlock Detection: Other studies focus on optimizing the performance of tracing to analyze \r\nsystem bottlenecks. \r\n<\/pre>\n","protected":false},"excerpt":{"rendered":"
ABOUT hung_task_all_cpu_backtrace If this option is set, the kernel will send an NMI to all CPUs to dump their backtraces when a hung task is detected. This file shows up if CONFIG_DETECT_HUNG_TASK and CONFIG_SMP are enabled. 0: Won\u2019t show all CPUs backtraces when a hung task is detected. This is the default behavior 1: Will … <\/p>\n
Continue reading “hung_task_all_cpu_backtrace( topic related to CPUs dumping  their backtraces )”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[73,126],"tags":[],"_links":{"self":[{"href":"https:\/\/www.trueangle.org\/index.php\/wp-json\/wp\/v2\/posts\/20488"}],"collection":[{"href":"https:\/\/www.trueangle.org\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.trueangle.org\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.trueangle.org\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.trueangle.org\/index.php\/wp-json\/wp\/v2\/comments?post=20488"}],"version-history":[{"count":44,"href":"https:\/\/www.trueangle.org\/index.php\/wp-json\/wp\/v2\/posts\/20488\/revisions"}],"predecessor-version":[{"id":20600,"href":"https:\/\/www.trueangle.org\/index.php\/wp-json\/wp\/v2\/posts\/20488\/revisions\/20600"}],"wp:attachment":[{"href":"https:\/\/www.trueangle.org\/index.php\/wp-json\/wp\/v2\/media?parent=20488"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.trueangle.org\/index.php\/wp-json\/wp\/v2\/categories?post=20488"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.trueangle.org\/index.php\/wp-json\/wp\/v2\/tags?post=20488"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}