Messages in this thread | | | Date | Sat, 5 Nov 2005 20:20:41 +0800 | From | Yan Zheng <> | Subject | Re: Question about the usage of kernel_thread |
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> > AFAIK the thread created like above is a true kernel thread but in > general practice what I saw and used that by creating thread from > init_module, the thread first call daemonize which actually drops the > mm related to thread and then through reparent_to_init it makes init > as a parent of the thread/process newly created. So after daemonize > call current->mm becomes NULL and when the scheduling is going to be > done the previous_process->mm will be used as the current->mm and > creating thread like above is correct. > > -- > Fawad Lateef > -
Thank you very much, Fawad.
I do additional test by follow codes, the result is strange.
======================================== #include <linux/kernel.h> #include <linux/module.h>
static int noop(void *dummy) { int i = 0; while(i++ < 10) { printk("current->mm = %p\n", current->mm); printk("current->active_mm = %p\n", current->active_mm); set_current_state(TASK_INTERRUPTIBLE); schedule_timeout(HZ); } return 0; }
static void create_thread(void *dummy) { kernel_thread(noop, NULL, CLONE_KERNEL | SIGCHLD); }
static struct work_struct work;
static int test_init(void) { INIT_WORK(&work, create_thread, NULL); schedule_work(&work); return 0; } /* static int test_init(void) { kernel_thread(noop, NULL, CLONE_KERNEL | SIGCHLD); return 0; } */
static void test_exit(void) {} module_init(test_init); module_exit(test_exit); ========================================
If use kernel_thread like above. the output is: current->mm = 00000000 current->active_mm = dffd2640 current->mm = 00000000 current->active_mm = df4d50e0 current->mm = 00000000 current->active_mm = df4463c0 current->mm = 00000000 current->active_mm = df4d50e0 current->mm = 00000000 current->active_mm = c16ee3e0 current->mm = 00000000 current->active_mm = df4463c0 current->mm = 00000000 current->active_mm = c16ee3e0 current->mm = 00000000 current->active_mm = c16ee3e0 current->mm = 00000000 current->active_mm = df796380 current->mm = 00000000 current->active_mm = c16ee3e0
if use kernel_thread directly in module_init(...). the output is: current->mm = df988060 current->active_mm = df988060 current->mm = df988060 current->active_mm = df988060 current->mm = df988060 current->active_mm = df988060 current->mm = df988060 current->active_mm = df988060 current->mm = df988060 current->active_mm = df988060 current->mm = df988060 current->active_mm = df988060 current->mm = df988060 current->active_mm = df988060 current->mm = df988060 current->active_mm = df988060 current->mm = df988060 current->active_mm = df988060 current->mm = df988060 current->active_mm = df988060
Would you please do some explanation.
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