Kthread and Signal ================================= .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Topics in this section, * :ref:`Version Info ` * :ref:`Learnings in this section ` * :ref:`Explanation of kthread APIs ` * :ref:`kthread_should_stop ` * :ref:`kthread_run ` * :ref:`kthread_stop ` * :ref:`Explanation of Waitqueue APIs ` * :ref:`DECLARE_WAIT_QUEUE_HEAD ` * :ref:`wait_event_interruptible ` * :ref:`Explanation of Signal APIs ` * :ref:`allow_signal ` * :ref:`signal_pending ` * :ref:`sigaddset ` * :ref:`send_signal ` * :ref:`flush_signals ` * :ref:`Explanation of miscellaneous APIs ` * :ref:`Module parameter APIs ` * :ref:`IS_ERR ` * :ref:`pr_info ` * :ref:`wake_up_process ` * :ref:`msleep ` * :ref:`Driver entry point APIs ` * :ref:`Example 1: Waiting for an event using wait_event_killable ` * :ref:`List of headers ` * :ref:`Module Macros ` * :ref:`Initialize thread variables ` * :ref:`Module init function ` * :ref:`Thread start function ` * :ref:`Module exit function ` * :ref:`Thread stop function ` * :ref:`Thread function API ` * :ref:`Signal Handling API ` * :ref:`Driver entry points ` * :ref:`See the full program below ` * :ref:`Makefile ` * :ref:`Compile and Load the module ` * :ref:`Summary of Kthread APIs ` * :ref:`Summary of Workqueue APIs ` * :ref:`Summary of Miscellaneous APIs ` .. _kthread_signal_0: .. tab-set:: .. tab-item:: Version Info =============================== ======================================= # Version =============================== ======================================= Ubuntu Ubuntu 22.10 Kernel 6.7.9 =============================== ======================================= .. _kthread_signal_1: .. tab-set:: .. tab-item:: Learnings in this section * In this program, you are going to learn .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow * How to send signal? .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow * How to send signal from one thread to another thread using signal APIs? .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow * How to use Kthread APIs ? * `kthread_should_stop `_ * `kthread_run `_ * `kthread_stop `_ .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow * How to use Waitqueue APIs ? * `DECLARE_WAIT_QUEUE_HEAD `_ * `wake_up `_ * `wait_event_interruptible `_ .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow * How to use Signal APIs ? * `allow_signal `_ * `signal_pending `_ * `sigaddset `_ * `send_sig `_ * `flush_signals `_ .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow * How to use below APIs ? * `MODULE_LICENSE `_ * `MODULE_DESCRIPTION `_ * `MODULE_AUTHOR `_ * `IS_ERR `_ * `pr_info `_ * `wake_up_process `_ * `msleep `_ * `module_init `_ * `module_exit `_ .. _kthread_signal_2: .. tab-set:: .. tab-item:: Explanation of Kthread APIs .. _kthread_signal_5: .. tab-set:: .. tab-item:: kthread_should_stop * Here is the function prototype of the API: `kthread_should_stop `_ .. code-block:: c #include bool kthread_should_stop(void); * where * `kthread_should_stop `_: this is used to determine whether the thread should return now. Whenever the `kthread_stop() `_ is called it will be woken and returns true. * return type: returns true when the thread is stopped, false when the thread is still in execution * Here is an example of how to use the API, .. code-block:: c while (!kthread_should_stop()) { //add the instructions to be performed during thread execution. } .. _kthread_signal_6: .. tab-set:: .. tab-item:: kthread_run * Here is the function prototype of the API: `kthread_run `_ .. code-block:: c #include #define kthread_run(threadfn, data, namefmt, ...) * where * `kthread_run `_ : is used to create and wake a kthread * return type: struct task_struct* (i.e) address of the kthread * threadfn: function to executed by kthread * data: data pointer for threadfn which can be used to send any possible arguments required for threadfn. * namefmt: printf-style format for the thread name which will be displayed on ps output when the thread is in execution. * Here is an example of how to use the API, .. code-block:: c kthread_run(mythread,NULL,"sample kthread"); .. _kthread_signal_7: .. tab-set:: .. tab-item:: kthread_stop * Here is the function prototype of the API: `kthread_stop `_ .. code-block:: c #include int kthread_stop(struct task_struct *k); * where * `kthread_stop `_: stops a kthread. * return type: returns the return value of threadfn() which is passed as an argument during kthread creation. * k: kthread created by one of the API used to created kthread. * Here is the example of how to use the API, .. code-block:: c kthread_stop(mythread); .. _kthread_signal_82: .. tab-set:: .. tab-item:: Explanation of Waitqueue APIs .. _kthread_signal_83: .. tab-set:: .. tab-item:: DECLARE_WAIT_QUEUE_HEAD * Here is the prototype of the API: `DECLARE_WAIT_QUEUE_HEAD `_ .. code-block:: c # include #define DECLARE_WAIT_QUEUE_HEAD(name) \ struct wait_queue_head name = __WAIT_QUEUE_HEAD_INITIALIZER(name) * where * `DECLARE_WAIT_QUEUE_HEAD `_ : To declare and initialize wait queue head. * name : name which is given to the wait queue head on declaration. * Here is the example of the API, .. code-block:: c DECLARE_WAIT_QUEUE_HEAD(mywaitqueue); .. _kthread_signal_118: .. tab-set:: .. tab-item:: wait_event_interruptible * Here is the prototype of the API: `wait_event_interruptible `_ .. code-block:: c # include #define wait_event_interruptible(wq_head, condition) * where * `wait_event_interruptible `_ : sleep until a condition gets true * wq_head: the waitqueue to wait on * condition: a C expression for the event to wait for * Here is an example of the API .. code-block:: c wait_event_interruptible(mywq_head,i < 10); .. _kthread_signal_28: .. tab-set:: .. tab-item:: Explanation of signal APIs .. _kthread_signal_29: .. tab-set:: .. tab-item:: allow_signal * Here is the prototype of the API: `allow_signal `_ .. code-block:: c # include static inline void allow_signal(int sig); * where * `allow_signal `_ : used to know that the signal code will be handled, so that they don't get converted to SIGKILL or just silently dropped. * sig: signal code which will be handled. * Here is an example of how to use the API, .. code-block:: c allow_signal(SIGKILL); .. _kthread_signal_32: .. tab-set:: .. tab-item:: signal_pending * Here is the prototype of the API: `signal_pending `_ .. code-block:: c #include static inline int signal_pending(struct task_struct *p); * where * `signal_pending `_ : used to check for any pending signals queued for thread. * p: thread which needs to be checked for any pending signals being queued or not. * Here is an example of how to use the API, .. code-block:: c signal_pending(current); .. _kthread_signal_30: .. tab-set:: .. tab-item:: sigaddset * Here is the prototype of the API: `sigaddset `_ .. code-block:: c #include static inline void sigaddset(sigset_t *set, int _sig); * where * `sigaddset `_ : set the corresponding signal code bit in sigset_t. * set: the set for which the bit needs to be set. * _sig: signal code whose bit needs to be set in sigset_t. * Here is an example of how to use the API .. code-block:: c sigaddset(current->signal->shared_pending.signal,SIGKILL); .. _kthread_signal_31: .. tab-set:: .. tab-item:: send_sig * Here is the prototype of the API: `send_sig `_ .. code-block:: c #include int send_sig(int sig, struct task_struct *p, int priv); * where * `send_sig `_ : send signal to a thread * sig: signal code which needs to be sent * p: receiver thread which receives the signal sent. * Here is an example of how to use the API .. code-block:: c send_sig(SIGKILL,receiver_thread,0); .. _kthread_signal_33: .. tab-set:: .. tab-item:: flush_signals * Here is the prototype of the API: `flush_signals `_ .. code-block:: c #include void flush_signals(struct task_struct *t); * where * `flush_signals `_ : Flush all pending signals for this kthread. * t: thread whose signals needs to be flushed. * Here is an example of the API .. code-block:: c flush_signals(current); .. _kthread_signal_8: .. tab-set:: .. tab-item:: Explanation of miscellaneous APIs .. _kthread_signal_9: .. tab-set:: .. tab-item:: Module parameter APIs * Here is the prototype of module paramter APIs .. code-block:: c #include #define MODULE_LICENSE(_license) MODULE_FILE MODULE_INFO(license, _license) #define MODULE_AUTHOR(_author) MODULE_INFO(author, _author) #define MODULE_DESCRIPTION(_description) MODULE_INFO(description, _description) * where * `MODULE_LICENSE `_: tells the kernel what license is used by our module. * `MODULE_AUTHOR `_: denotes the author of this kernel module. * `MODULE_DESCRIPTION `_: gives a basic idea about what the kernel module does. * These information can be found when modinfo command is used which lists out all these above mentioned information. * Here is the example of how to use the Module parameter APIs, .. code-block:: c MODULE_LICENSE("GPL"); MODULE_AUTHOR("Linux Usr"); MODULE_DESCRIPTION("Sample kernel module"); .. _kthread_signal_10: .. tab-set:: .. tab-item:: IS_ERR * Here is the prototype of the API: `IS_ERR `_ .. code-block:: c #include static inline bool __must_check IS_ERR(__force const void *ptr); * where * `IS_ERR `_: Detects an error pointer * return type: return true if it's an error pointer else return false. * ptr: pointer which needs to detected. * Here is an example of how to use the API, .. code-block:: c if(IS_ERR(sample_ptr)) { //instructions to be executed when error ptr is detected } else { //instructions to be executed when error ptr is not detected } .. _kthread_signal_11: .. tab-set:: .. tab-item:: pr_info * Here is the prototype of the API: `pr_info `_ .. code-block:: c #include #define pr_info(fmt, ...) \ printk(KERN_INFO pr_fmt(fmt), ##__VA_ARGS__) * where * `pr_info `_: Prints an info-level messages * fmt: format string * Here is an example of how to use the API, .. code-block:: c pr_info("//sample print statement"); .. _kthread_signal_12: .. tab-set:: .. tab-item:: wake_up_process * Here is the example of the API: `wake_up_process `_ .. code-block:: c #include extern int wake_up_process(struct task_struct *tsk); * where * `wake_up_process `_: wake up a specific process * return type: returns 1 if the process is woken up, 0 if the process is in running state. * tsk: process to be woken up. * Here is the example of how to use the API, .. code-block:: c wake_up_process(mythread); .. _kthread_signal_13: .. tab-set:: .. tab-item:: msleep * Here is the example of the API: `msleep `_ .. code-block:: c #include void msleep(unsigned int msecs); * where * `msleep `_: will put it in sleep for a certain amount of msecs time. * msecs: time in milliseconds to sleep for * Here is the example of how to use the API, .. code-block:: c msleep(1000); .. _kthread_signal_14: .. tab-set:: .. tab-item:: Driver entry point API's * Here is the prototype of the Driver entry point API's .. code-block:: c #include #define module_init(x) __initcall(x); #define module_exit(x) __exitcall(x); * where * `module_init `_: driver initialization entry point which will be called at module insertion time. * `module_exit `_: driver exit entry point which will be called during the removal of module. * x: * function to be run at module insertion for `module_init `_ function. * function to be run when driver is removed for `module_exit `_ function. * Here is an example of how to use the driver entry point API's .. code-block:: c module_init(myinitmodule); module_exit(myexitmodule); .. _kthread_signal_15: .. tab-set:: .. tab-item:: Example 1: Sending signals between threads * In this example let's see how to send signals between threads and perform certain operation based on the signal received. .. _kthread_signal_16: .. tab-set:: .. tab-item:: List of headers * Include the follow header files(.h) to refer the API being used for the execution. .. code-block:: c #include #include #include #include #include #include #include #include #include .. _kthread_signal_17: .. tab-set:: .. tab-item:: Module macros * Add the following module macros to display information about the license, author and description about the module. .. code-block:: c MODULE_LICENSE("GPL"); MODULE_AUTHOR("Linux Usr"); MODULE_DESCRIPTION("sending signals between threads"); .. _kthread_signal_18: .. tab-set:: .. tab-item:: Initialize thread variables * Declare the thread and waitqueue variables which we are going to create and use in this example .. code-block:: c #define MAX_SIGNAL_NOS 31 static int signal_list[MAX_SIGNAL_NOS]; DECLARE_WAIT_QUEUE_HEAD(recv_wait_queue); static struct task_struct *sender_thread; static struct task_struct *receiver_thread; .. _kthread_signal_19: .. tab-set:: .. tab-item:: Module init function * Add the module init function which will be executed once we load the kernel module using insmod command. .. code-block:: c static int __init kthread_signal_init(void) { pr_info("Inside thread init function\n"); thread_start(); return 0; } .. _kthread_signal_20: .. tab-set:: .. tab-item:: Thread start function * Add the thread start function which is called from module init function, creates the thread and starts it's execution. .. code-block:: c void thread_start(void) { int i; pr_info("inside kthread init function\n"); for(i = 0; i < MAX_SIGNAL_NOS; i++) signal_list[i] = i+1; receiver_thread = kthread_run(recv_thread_fn,NULL,"kthread_signal receiver_thread example"); if (IS_ERR(receiver_thread)) pr_info("error in creating receiver thread\n"); else pr_info("successfully created receiver thread\n"); sender_thread = kthread_run(sender_thread_fn,NULL,"kthread_signal sender_thread example"); if (IS_ERR(sender_thread)) pr_info("error in creating sender thread\n"); else pr_info("successfully created sender thread\n"); } .. _kthread_signal_21: .. tab-set:: .. tab-item:: Module exit function * Add the module exit function which will be executed once we unload the kernel module using rmmod command. .. code-block:: c static void __exit kthread_signal_exit(void) { pr_info("Inside kthread exit function\n"); thread_stop(); } .. _kthread_signal_22: .. tab-set:: .. tab-item:: Thread stop function * Add the thread stop function which is called from module exit function, destroys the thread created and stops it's execution. .. code-block:: c void thread_stop(void) { if(sender_thread) kthread_stop(sender_thread); if(receiver_thread) kthread_stop(receiver_thread); pr_info("destroyed threads\n"); } .. _kthread_signal_23: .. tab-set:: .. tab-item:: Thread function API * Add the thread function API which will be called as soon as the kthread is created and is in running state. .. code-block:: c static int recv_thread_fn (void *data) { long unsigned int *signum; int j; for (j = 0;jsignal->shared_pending.signal.sig; for (int i = 0; i <= MAX_SIGNAL_NOS; i++) { if ((*signum & 1 << i) >> i == 1) { handle_signal(i+1); break; } } flush_signals(current); msleep(1000); } return 0; } static int sender_thread_fn (void *data) { int random_num; pr_info("sending signal from sender thread -> receiver thread\n"); while (!kthread_should_stop()) { random_num = get_random_u32() % 32; sigaddset(&receiver_thread->signal->shared_pending.signal,signal_list[random_num]); send_sig(signal_list[random_num],receiver_thread,0); msleep(1000); } return 0; } .. _kthread_signal_34: .. tab-set:: .. tab-item:: Signal Handling API * This API gives the set of instructions on how to handle each signal. .. code-block:: c static void handle_signal(int signum) { switch(signum) { case SIGHUP: pr_info("executing sighup instructions\n"); break; case SIGINT: pr_info("executing sigint instructions\n"); break; case SIGQUIT: pr_info("executing sigquit instructions\n"); break; case SIGILL: pr_info("executing sigill instructions\n"); break; case SIGTRAP: pr_info("executing sigtrap instructions\n"); break; case SIGABRT: pr_info("executing sigabrt instructions\n"); break; case SIGBUS: pr_info("executing sigbus instructions\n"); break; case SIGFPE: pr_info("executing sigfpe instructions\n"); break; case SIGKILL: pr_info("executing sigkill instructions\n"); break; case SIGUSR1: pr_info("executing sigusr1 instructions\n"); break; case SIGSEGV: pr_info("executing sigsegv instructions\n"); break; case SIGUSR2: pr_info("executing sigusr2 instructions\n"); break; case SIGPIPE: pr_info("executing sigpipe instructions\n"); break; case SIGALRM: pr_info("executing sigalrm instructions\n"); break; case SIGTERM: pr_info("executing sigterm instructions\n"); break; case SIGSTKFLT: pr_info("executing sigstkflt instructions\n"); break; case SIGCHLD: pr_info("executing sigchld instructions\n"); break; case SIGCONT: pr_info("executing sigcont instructions\n"); break; case SIGSTOP: pr_info("executing sigstop instructions\n"); break; case SIGTSTP: pr_info("executing sigtstp instructions\n"); break; case SIGTTIN: pr_info("executing sigttfin instructions\n"); break; case SIGTTOU: pr_info("executing sigttou instructions\n"); break; case SIGURG: pr_info("executing sigurg instructions\n"); break; case SIGXCPU: pr_info("executing sigxcpu instructions\n"); break; case SIGXFSZ: pr_info("executing sigxfsz instructions\n"); break; case SIGVTALRM: pr_info("executing sigvtalrm instructions\n"); break; case SIGPROF: pr_info("executing sigprof instructions\n"); break; case SIGWINCH: pr_info("executing sigwinch instructions\n"); break; case SIGPOLL: pr_info("executing sigpoll instructions\n"); break; case SIGPWR: pr_info("executing sigpwr instructions\n"); break; case SIGSYS: pr_info("executing sigsys instructions\n"); break; default: break; } } .. _kthread_signal_24: .. tab-set:: .. tab-item:: Driver entry points * Add the driver entry points which will be executed once the module is inserted or removed from the kernel. .. code-block:: c module_init(kthread_signal_init); module_exit(kthread_signal_exit); .. _kthread_signal_25: .. tab-set:: .. tab-item:: See the full program below .. tab-set:: .. tab-item:: kthread.c .. literalinclude:: kthread.c :language: c :linenos: .. _kthread_signal_26: .. tab-set:: .. tab-item:: Makefile .. literalinclude:: Makefile :language: c :linenos: .. _kthread_signal_27: .. tab-set:: .. tab-item:: Compile and load the module * Run make to compile the kernel source and generate the .ko image. .. code-block:: shell make -C /lib/modules/6.7.9/build M=$HOME/kthread_examples/ make[1]: Entering directory '/usr/src/linux-headers-6.7.9' warning: the compiler differs from the one used to build the kernel The kernel was built by: x86_64-linux-gnu-gcc (Ubuntu 12.2.0-3ubuntu1) 12.2.0 You are using: gcc (Ubuntu 12.2.0-3ubuntu1) 12.2.0 CC [M] $HOME/kthread_examples/kthread.o MODPOST $HOME/kthread_examples/Module.symvers CC [M] $HOME/kthread_examples/kthread.mod.o LD [M] $HOME/kthread_examples/kthread.ko BTF [M] $HOME/kthread_examples/kthread.ko Skipping BTF generation for $HOME/kthread_examples/kthread.ko due to unavailability of vmlinux make[1]: Leaving directory '/usr/src/linux-headers-6.7.9' * Check if the .ko is generated or not using ls command. .. code-block:: shell test@test-V520-15IKL:~$ ls -l total 360 -rw-rw-r-- 1 test test 713 Mar 18 16:06 kthread.c -rw-rw-r-- 1 test test 169784 Mar 18 16:08 kthread.ko -rw-rw-r-- 1 test test 58 Mar 18 16:08 kthread.mod -rw-rw-r-- 1 test test 1047 Mar 18 16:08 kthread.mod.c -rw-rw-r-- 1 test test 96512 Mar 18 16:08 kthread.mod.o -rw-rw-r-- 1 test test 74696 Mar 18 16:08 kthread.o -rw-rw-r-- 1 test test 161 Mar 18 16:00 Makefile -rw-rw-r-- 1 test test 58 Mar 18 16:08 modules.order -rw-rw-r-- 1 test test 0 Mar 18 16:08 Module.symvers * Run modinfo command to get the information about the kernel module. .. code-block:: shell test@test-V520-15IKL:~/.../tc_1$ modinfo kthread.ko filename: $HOME/kthread_examples/kthread.ko description: sending signals between threads author: Linux Usr license: GPL srcversion: 8D2147F67AB01CF0E482DAC depends: retpoline: Y name: kthread vermagic: 6.7.9 SMP preempt mod_unload modversions * insert the module using insmod command. .. code-block:: shell test@test-V520-15IKL:~$ sudo insmod ./kthread.ko * check if the module is loaded or not using lsmod command. .. code-block:: shell test@test-V520-15IKL:~$ sudo lsmod | grep kthread kthread 16384 0 * check if the thread is created or not using ps command. .. code-block:: shell test@test-V520-15IKL:~$ ps -N | grep kthread_signal 14226 ? 00:00:00 kthread_signal receiver_thread example 14227 ? 00:00:00 kthread_signal sender_thread example * check for the kernel messages from init function and thread function once the module is loaded and thread is created. .. code-block:: shell test@test-V520-15IKL:~$ sudo dmesg [ 2535.581826] inside kthread init function [ 2535.581830] inside kthread init function [ 2535.581866] successfully created receiver thread [ 2535.581883] successfully created sender thread [ 2535.581885] sending signal from sender thread -> receiver thread [ 2535.581892] executing sigcont instructions [ 2536.604333] executing sigpipe instructions [ 2537.628340] executing sigurg instructions [ 2538.652358] executing sigcont instructions [ 2539.676403] executing sigint instructions [ 2540.700430] executing sigttfin instructions * remove the module from kernel using rmmod command. .. code-block:: shell test@test-V520-15IKL:~$ sudo rmmod kthread * check if the module is still loaded after removing the kernel module using lsmod if it is not displayed in lsmod output it is verified that the module is removed successfully. .. code-block:: shell test@test-V520-15IKL:~$ sudo lsmod | grep kthread test@test-V520-15IKL:~$ * check if the thread is destroyed using ps command if it is not displayed in ps output we can confirm that the thread is destroyed successfully. .. code-block:: shell test@test-V520-15IKL:~$ ps -N | grep kthread_signal test@test-V520-15IKL:~$ * Check for kernel messages from exit function using dmesg command. .. code-block:: shell test@test-V520-15IKL:~$ sudo dmesg [ 2553.059738] inside kthread exit function [ 2555.036884] destroyed threads .. _kthread_signal_80: .. tab-set:: .. tab-item:: Summary of Kthread APIs =============================== ======================================= kthread API Learning =============================== ======================================= kthread_run Create and wake a thread kthread_should_stop To determine when thread should exit kthread_stop Stop a thread created by kthread_create =============================== ======================================= .. _kthread_signal_90: .. tab-set:: .. tab-item:: Summary of Workqueue APIs ================================= ================================================================================== Workqueue API Learning ================================= ================================================================================== DECLARE_WAIT_QUEUE_HEAD Declare waitqueue head wait_event_interruptible sleeps until the condition is true ================================= ================================================================================== .. _kthread_signal_92: .. tab-set:: .. tab-item:: Summary of Signal APIs =============================== =============================================== Signal API Learning =============================== =============================================== allow_signal used to allow signal so that it can be handled signal_pending check for pending signals sigaddset set the corresponding signal code bit send_sig sending signal to thread flush_signals flush all pending signals =============================== =============================================== .. _kthread_signal_81: .. tab-set:: .. tab-item:: Summary of miscellaneous APIs =============================== =========================================================================================== API Learning =============================== =========================================================================================== MODULE_LICENSE Used to denote the license used in the kernel module MODULE_AUTHOR Used to mention the author of the kernel module MODULE_DESCRIPTION Used to describe what the module does IS_ERR Detects an error pointer wake_up_process wake up a specific process msleep will put in sleep for a certain amount of msecs time. module_init Driver initialization entry point module_exit Driver exit entry point pr_info Print an info-level message =============================== ===========================================================================================