Feast of Saint Mark, evangelist
hung_task_all_cpu_backtrace( topic related to CPUs dumping their backtraces )
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’t show all CPUs backtraces when a hung task is detected. This is the default behavior 1: Will non-maskably interrupt all CPUs and dump their backtraces when a hung task is detected.
LINUX KERNEL RELATED PARAMETER
$cat /proc/sys/kernel/hung_task_all_cpu_backtrace
0
$echo 1 | sudo tee –append /proc/sys/kernel/hung_task_all_cpu_backtrace
[sudo] password for jeffrin:
1
$cat /proc/sys/kernel/hung_task_all_cpu_backtrace
1
$
PARAMETER RELATED
USERSPACE PROCESS BACKTRACE
(gdb) bt
#0 __syscall_cancel_arch () at ../sysdeps/unix/sysv/linux/x86_64/syscall_cancel.S:56
#1 0x00007ffff64197a4 in __internal_syscall_cancel
(a1=
#2 0x00007ffff64197ed in __syscall_cancel
(a1=
#3 0x00007ffff648f29e in __GI_ppoll
(fds=
#4 0x00007ffff7951b34 in ??? () at /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#5 0x00007ffff7952210 in g_main_context_iteration ()
at /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#6 0x00007ffff76fe13d in g_application_run ()
at /usr/lib/x86_64-linux-gnu/libgio-2.0.so.0
#7 0x000055555580dfad in app_run ()
#8 0x0000555555641f3b in main ()
(gdb)
BACKTRACE FROM LINUX KERNEL SPACE
echo 1 | sudo tee /proc/sys/kernel/sysrq
echo l | sudo tee /proc/sysrq-trigger.
dmesg
[30208.196481] sysrq: Show backtrace of all active CPUs
[30208.196491] NMI backtrace for cpu 0
[30208.196494] CPU: 0 UID: 0 PID: 45306 Comm: tee Not tainted 6.18.20-rc1+ #61 PREEMPT(lazy)
[30208.196498] Hardware name: HP HP Laptop 15s-ey1xxx/8706, BIOS F.61 03/25/2022
[30208.196500] Call Trace:
[30208.196503] <TASK>code
[30208.196507] dump_stack_lvl+0x5d/0x80
[30208.196514] nmi_cpu_backtrace.cold+0x18/0x65
[30208.196518] ? __pfx_nmi_raise_cpu_backtrace+0x10/0x10
[30208.196524] nmi_trigger_cpumask_backtrace+0xf4/0x110
[30208.196529] __handle_sysrq.cold+0x8a/0x160
[30208.196534] write_sysrq_trigger+0x59/0xa0
[30208.196540] proc_reg_write+0x5a/0xb0
[30208.196544] vfs_write+0xce/0x480
[30208.196552] ksys_write+0x73/0xf0
[30208.196556] do_syscall_64+0x81/0x7f0
[30208.196562] ? srso_return_thunk+0x5/0x5f
[30208.196565] ? __x64_sys_openat+0x61/0xa0
[30208.196569] ? srso_return_thunk+0x5/0x5f
[30208.196571] ? do_syscall_64+0xb9/0x7f0
[30208.196576] ? srso_return_thunk+0x5/0x5f
[30208.196579] ? ksys_fadvise64_64+0x6c/0xa0
[30208.196584] ? srso_return_thunk+0x5/0x5f
[30208.196587] ? srso_return_thunk+0x5/0x5f
[30208.196589] ? do_syscall_64+0xb9/0x7f0
[30208.196593] ? srso_return_thunk+0x5/0x5f
[30208.196597] ? do_user_addr_fault+0x21a/0x690
[30208.196602] ? srso_return_thunk+0x5/0x5f
[30208.196605] ? srso_return_thunk+0x5/0x5f
[30208.196609] entry_SYSCALL_64_after_hwframe+0x76/0x7e
[30208.196613] RIP: 0033:0x7f8875a3a7d2
[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
[30208.196640] RSP: 002b:00007fffda92a5b0 EFLAGS: 00000202 ORIG_RAX: 0000000000000001
[30208.196644] RAX: ffffffffffffffda RBX: 000055b4a7c9c310 RCX: 00007f8875a3a7d2
[30208.196645] RDX: 0000000000000002 RSI: 00007fffda92a750 RDI: 0000000000000003
[30208.196647] RBP: 0000000000000002 R08: 0000000000000000 R09: 0000000000000000
[30208.196649] R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000002
[30208.196650] R13: 00007fffda92a750 R14: 00007fffda92a750 R15: 0000000000000002
[30208.196659] </TASK>
[30208.196688] Sending NMI from CPU 0 to CPUs 1-3:
[30208.196697] NMI backtrace for cpu 1
[30208.196699] CPU: 1 UID: 0 PID: 345 Comm: systemd-journal Not tainted 6.18.20-rc1+ #61 PREEMPT(lazy)
[30208.196702] Hardware name: HP HP Laptop 15s-ey1xxx/8706, BIOS F.61 03/25/2022
[30208.196703] RIP: 0033:0x7f51c5e71490
[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
[30208.196712] RSP: 002b:00007ffc7ed4ca08 EFLAGS: 00000246
[30208.196714] RAX: 0000000000000000 RBX: 000056303827baf0 RCX: 0000000000000000
[30208.196716] RDX: 00007ffc7ed4ca18 RSI: 00007ffc7ed4ca20 RDI: 0000000000000000
[30208.196717] RBP: 00007ffc7ed4ca20 R08: 00007f51c62b3070 R09: 0000000000000000
[30208.196718] R10: 00007f51c62b3000 R11: 0000000000c1eb8a R12: 000056303827baf0
[30208.196720] R13: 0000000000000000 R14: ffffffffffffffff R15: 000056302ba21658
[30208.196721] FS: 00007f51c6172840 GS: 0000000000000000
[30208.196723] NMI backtrace for cpu 2 skipped: idling at io_idle+0x3/0x30
[30208.196736] NMI backtrace for cpu 3
[30208.196741] CPU: 3 UID: 0 PID: 806 Comm: in:imklog Not tainted 6.18.20-rc1+ #61 PREEMPT(lazy)
[30208.196749] Hardware name: HP HP Laptop 15s-ey1xxx/8706, BIOS F.61 03/25/2022
[30208.196752] RIP: 0010:vsnprintf+0x355/0x5e0
[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
[30208.196765] RSP: 0018:ffffd0d14ce93878 EFLAGS: 00000286
[30208.196771] RAX: ffffd0d14ce93992 RBX: ffffffff9358ebf2 RCX: 000000000000003e
[30208.196775] RDX: 0000000000000000 RSI: ffffffff9358ebf1 RDI: ffffd0d14ce93992
[30208.196779] RBP: ffffd0d14ce938e8 R08: 0000000000000001 R09: 00000000ffffffff
[30208.196782] R10: 0000000000000000 R11: 0000000000000004 R12: ffffffff9358ebf2
[30208.196785] R13: 0000000000000400 R14: 0000000000000400 R15: ffffffff9358ebf1
[30208.196789] FS: 00007f2e35a6b6c0(0000) GS:ffff8f48445af000(0000) knlGS:0000000000000000
[30208.196794] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[30208.196798] CR2: 000055b82387b970 CR3: 000000010a0e0000 CR4: 00000000003506f0
[30208.196802] Call Trace:
[30208.196805] <TASK>
[30208.196818] sprintf+0x5f/0x80
[30208.196828] ? srso_return_thunk+0x5/0x5f
[30208.196837] info_print_prefix+0x57/0xe0
[30208.196846] record_print_text+0x7a/0x170
[30208.196860] syslog_print+0x274/0x360
[30208.196869] ? __pfx_autoremove_wake_function+0x10/0x10
[30208.196886] do_syslog+0xd5/0x400
[30208.196900] ? srso_return_thunk+0x5/0x5f
[30208.196910] kmsg_read+0x57/0x70
[30208.196918] ? srso_return_thunk+0x5/0x5f
[30208.196924] ? __pfx_kmsg_read+0x10/0x10
[30208.196930] vfs_read+0xbf/0x390
[30208.196937] ? __seccomp_filter+0x42/0x590
[30208.196953] ksys_read+0x73/0xf0
[30208.196963] do_syscall_64+0x81/0x7f0
[30208.196972] ? srso_return_thunk+0x5/0x5f
[30208.196978] ? srso_return_thunk+0x5/0x5f
[30208.196984] ? wakeup_preempt+0x89/0xa0
[30208.196992] ? srso_return_thunk+0x5/0x5f
[30208.196998] ? ttwu_do_activate+0x86/0x250
[30208.197005] ? srso_return_thunk+0x5/0x5f
[30208.197010] ? update_rq_clock+0x81/0x180
[30208.197019] ? srso_return_thunk+0x5/0x5f
[30208.197024] ? try_to_wake_up+0x371/0x8b0
[30208.197032] ? srso_return_thunk+0x5/0x5f
[30208.197037] ? plist_del+0x5f/0xd0
[30208.197046] ? srso_return_thunk+0x5/0x5f
[30208.197052] ? wake_up_q+0x37/0x90
[30208.197059] ? srso_return_thunk+0x5/0x5f
[30208.197064] ? futex_wake+0xac/0x1c0
[30208.197077] ? srso_return_thunk+0x5/0x5f
[30208.197082] ? srso_return_thunk+0x5/0x5f
[30208.197088] ? __x64_sys_futex+0x12d/0x210
[30208.197101] ? srso_return_thunk+0x5/0x5f
[30208.197106] ? do_syscall_64+0xb9/0x7f0
[30208.197114] ? srso_return_thunk+0x5/0x5f
[30208.197120] ? switch_fpu_return+0x5b/0xe0
[30208.197128] ? srso_return_thunk+0x5/0x5f
[30208.197134] ? do_syscall_64+0x240/0x7f0
[30208.197146] ? srso_return_thunk+0x5/0x5f
[30208.197151] ? do_syscall_64+0xb9/0x7f0
[30208.197158] ? __irq_exit_rcu+0x3d/0xe0
[30208.197164] ? srso_return_thunk+0x5/0x5f
[30208.197172] entry_SYSCALL_64_after_hwframe+0x76/0x7e
[30208.197177] RIP: 0033:0x7f2e35fd3ffe
[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
[30208.197199] RSP: 002b:00007f2e35a4a3b8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
[30208.197205] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f2e35fd3ffe
[30208.197208] RDX: 0000000000001fa0 RSI: 00007f2e35a4ac30 RDI: 0000000000000005
[30208.197211] RBP: 00007f2e35a4b9c3 R08: 0000000000000000 R09: 0000000000000000
[30208.197214] R10: 0000000000000000 R11: 0000000000000246 R12: 000056345780d7a0
[30208.197217] R13: 00007f2e35a4ac30 R14: 0000000000001fa0 R15: 00007f2e35a4ac30
[30208.197232] </TASK>
SHELL CLASS ROOM
$pidof gimp
75203
$$sudo cat /proc/75203/stack
cat: /proc/75203/stack: Permission denied
$sudo cat /proc/75203/stack
[sudo] password for jeffrin:
[<0>] poll_schedule_timeout.constprop.0+0x37/0x90
[<0>] do_sys_poll+0x3fc/0x590
[<0>] __x64_sys_ppoll+0xdf/0x180
[<0>] do_syscall_64+0x81/0x7f0
[<0>] entry_SYSCALL_64_after_hwframe+0x76/0x7e
$kill -STOP 75203
$sudo cat /proc/75203/stack
[<0>] do_signal_stop+0x16f/0x200
[<0>] get_signal+0x230/0x920
[<0>] arch_do_signal_or_restart+0x41/0x260
[<0>] exit_to_user_mode_loop+0x8a/0x130
[<0>] do_syscall_64+0x206/0x7f0
[<0>] entry_SYSCALL_64_after_hwframe+0x76/0x7e
$kill -CONT 75203
$sudo cat /proc/75203/stack
[<0>] poll_schedule_timeout.constprop.0+0x37/0x90
[<0>] do_sys_poll+0x3fc/0x590
[<0>] __x64_sys_ppoll+0xdf/0x180
[<0>] do_syscall_64+0x81/0x7f0
[<0>] entry_SYSCALL_64_after_hwframe+0x76/0x7e
$
What is do_signal_stop? do_signal_stop is an internal function in the Linux kernel (specifically in kernel/signal.c) that handles group stops. This occurs when a process receives a signal like SIGSTOP, SIGTSTP, SIGTTIN, or SIGTTOU, which tells the process to pause execution. Its primary responsibilities include: Transitioning State: It sets the process state to TASK_STOPPED. Managing Group Stops: If one thread in a thread group initiates a stop, this function ensures the entire group participates in the stop. Interaction with Debuggers: It handles special cases if a process is being traced by a debugger (like ptrace). Why is the address all zeros? When you see 0000000000000000, it usually indicates that kernel pointer restriction is enabled on your system. Security Feature: To prevent attackers from knowing where critical functions are located in memory (which could be used for exploits), the kernel hides the real addresses. kptr_restrict: This is controlled by the file /proc/sys/kernel/kptr_restrict. If the value is set to 1 or 2, non-privileged users will only see zeros for kernel symbols. Technical Context The "t" in the output stands for a local symbol in the text (code) section of the kernel binary. If it were a capital "T", it would be a global symbol. Are you currently troubleshooting a kernel crash or a frozen process where this function appeared in a stack trace?SOURCE: GOOGLE AI MODE
RELATED SOURCE CODE EXPOSURE
#ifdef CONFIG_SMP
{
.procname = "hung_task_all_cpu_backtrace",
.data = &sysctl_hung_task_all_cpu_backtrace,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = proc_dointvec_minmax,
.extra1 = SYSCTL_ZERO,
.extra2 = SYSCTL_ONE,
},
#endif /* CONFIG_SMP */
RELATED FROM GOOGLE AI MODE
The hung_task_all_cpu_backtrace feature is not derived from a traditional academic research paper, but
rather from a Linux kernel development initiative designed to improve debugging for blocked tasks (D-
state). This mechanism was introduced to decouple panic events from CPU backtrace dumps, allowing
developers to see what all CPUs are doing when a hung task is detected.
Key Details of hung_task_all_cpu_backtrace
Purpose: To aid in debugging complex hang scenarios (e.g., deadlocks) by providing a snapshot
of the entire system state, not just the stuck task.
Mechanism: It introduces a new sysctl (kernel.hung_task_all_cpu_backtrace) analogous to the
approaches used for soft/hard lockups.
Implementation: When hung_task_warnings are still active, this feature triggers a backtrace of
all CPUs upon detecting a task that has been in an uninterruptible sleep for longer than
hung_task_timeout_secs.
Context: It is part of the kernel/hung_task.c framework in the Linux kernel.
Related Research and Concepts
Kernel Tracing: Techniques like Ftrace and other tracers are heavily used to debug and reverse-
engineer complex systems, often used to determine the execution frequency of kernel paths.
Deadlock Detection: Other studies focus on optimizing the performance of tracing to analyze
system bottlenecks.
Hello world!
Welcome to WordPress. This is your first post. Edit or delete it, then start writing!
ls -ltr command to sort files by time
$ls
greedy-algorithm-example-coin-change-problem.js
longest-common-substring.js
memoization-top-down-approach.js
solving-knapsack-problem-a-recursive-solution.js
solving-knapsack-problem.js
tabulation-bottom-up-approach.js
$
ls shows the contents of the current directory
$ls -ltr
total 24
-rw-rw-r-- 1 jeffrin jeffrin 591 Feb 9 21:37 memoization-top-down-approach.js
-rw-rw-r-- 1 jeffrin jeffrin 436 Feb 9 21:56 tabulation-bottom-up-approach.js
-rw-rw-r-- 1 jeffrin jeffrin 2133 Feb 16 22:13 longest-common-substring.js
-rw-rw-r-- 1 jeffrin jeffrin 2288 Feb 18 21:54 solving-knapsack-problem.js
-rw-rw-r-- 1 jeffrin jeffrin 1303 Feb 19 22:24 solving-knapsack-problem-a-recursive-solution.js
-rw-rw-r-- 1 jeffrin jeffrin 1366 Feb 21 23:17 greedy-algorithm-example-coin-change-problem.js
$
-l use a long listing format
-r reverse order while sorting
-t sort by time, newest first
here you can see that the oldest date comes first because -r is given for reverse sorting.
Here you can see the latest file for checking new things.
What does bible say about slaves and masters ?
Create table on a database using python and MySQL
$python3 dt.py $cat dt.py # importing required library import mysql.connector # connecting to the database dataBase = mysql.connector.connect( host = "localhost", user = "jeff", passwd = "sixer", database = "learning" ) # preparing a cursor object cursorObject = dataBase.cursor() # creating table studentRecord = """CREATE TABLE STUDENT ( NAME VARCHAR(20) NOT NULL, BRANCH VARCHAR(50), ROLL INT NOT NULL, SECTION VARCHAR(5), AGE INT )""" # table created cursorObject.execute(studentRecord) # disconnecting from server dataBase.close() $mysql --user=jeff -psixer mysql: [Warning] Using a password on the command line interface can be insecure. Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 9 Server version: 8.0.30-1 (Debian) Copyright (c) 2000, 2022, Oracle and/or its affiliates. Oracle is a registered trademark of Oracle Corporation and/or its affiliates. Other names may be trademarks of their respective owners. Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. mysql> use learning; Reading table information for completion of table and column names You can turn off this feature to get a quicker startup with -A Database changed mysql> show tables; +--------------------+ | Tables_in_learning | +--------------------+ | STUDENT | +--------------------+ 1 row in set (0.00 sec) mysql> desc STUDENT; +---------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------+-------------+------+-----+---------+-------+ | NAME | varchar(20) | NO | | NULL | | | BRANCH | varchar(50) | YES | | NULL | | | ROLL | int | NO | | NULL | | | SECTION | varchar(5) | YES | | NULL | | | AGE | int | YES | | NULL | | +---------+-------------+------+-----+---------+-------+ 5 rows in set (0.20 sec) mysql>
Connect MySQL database using MySQL-Connector Python
$cat fdb.py import mysql.connector conn = mysql.connector.connect(host='localhost', database='learning', user='jeff', password='sixer') print(conn) conn.close $python3 fdb.py <mysql.connector.connection_cext.CMySQLConnection object at 0x7f143fc84790> $
Verifying MySQL Connector/Python installation
$python3 Python 3.10.6 (main, Aug 10 2022, 11:19:32) [GCC 12.1.0] on linux Type "help", "copyright", "credits" or "license" for more information. >>> import mysql.connector >>> >>> >>> mysql.connector.connect(host='localhost', ... database='learning', ... user='jeff', ... password='sixer') <mysql.connector.connection_cext.CMySQLConnection object at 0x7f9ddd630400> >>> $cat ted.py import mysql.connector mysql.connector.connect(host='localhost', database='learning', user='jeff', password='sixer') $
How to change root password of mysql on debian ?
$sudo mysql [sudo] password for jeffrin: Sorry, try again. [sudo] password for jeffrin: Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 8 Server version: 8.0.30-1 (Debian) Copyright (c) 2000, 2022, Oracle and/or its affiliates. Oracle is a registered trademark of Oracle Corporation and/or its affiliates. Other names may be trademarks of their respective owners. Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. mysql> ALTER USER 'root'@'localhost' IDENTIFIED BY 'unix'; Query OK, 0 rows affected (0.46 sec) mysql>