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POTask switching using a queue
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11014558
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0
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1
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11
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2012-06-13T12:11:38.657
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2012-06-17T10:59:54.813
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2012-06-17T10:59:54.813
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907685
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i'm developing my own hobby os, and now i'm stuck with a problem on the scheduler/task switching. I planned to use a FIFO queue as structure to hold processes. I implemented it using linked list. I also decided to use the iret method to switch from a task to another (so when the os was serving an interrupt request just before the iret i change the ESP register in order to move to the new task). But i have a problem. When the os start it launch two tasks: <ul> <li>idle</li> <li>shell</li> </ul> And with these two i have no problem. But if i try to launch two other tasks (with a simply printf inside), the task queue was corrupted. If after that i try to print the queue it print only two tasks that are the 2 just created and with idle and shell disappeared, but the os continues to work (i think that in a specific moment the esp field of the new tasks was replaced with the esp content of the shell). The task data structure is: <pre><code>typedef struct task_t{ pid_t pid; char name[NAME_LENGTH]; void (*start_function)(); task_state status; task_register_t *registers; unsigned int cur_quants; unsigned int eip; long int esp; unsigned int pdir; unsigned int ptable; struct task_t *next; }task_t; </code></pre> and the tss is: <pre><code>typedef struct { unsigned int edi; //+0 unsigned int esi; //+1 unsigned int ebp; //+2 unsigned int esp; //+3 (can be null) unsigned int ebx; //+4 unsigned int edx; //+5 unsigned int ecx; //+6 unsigned int eax; //+7 unsigned int eip; //+8 unsigned int cs; //+9 unsigned int eflags; //+10 unsigned int end; } task_register_t; </code></pre> The scheduler function is the following: <pre><code>void schedule(unsigned int *stack){ asm("cli"); if(active == TRUE){ task_t* cur_task = dequeue_task(); if(cur_task != NULL){ cur_pid = cur_task->pid; dbg_bochs_print("@@@@@@@"); dbg_bochs_print(cur_task->name); if(cur_task->status!=NEW){ cur_task->esp=*stack; } else { cur_task->status=READY; ((task_register_t *)(cur_task->esp))->eip = cur_task->eip; } enqueue_task(cur_task->pid, cur_task); cur_task=get_task(); if(cur_task->status==NEW){ cur_task->status=READY; } dbg_bochs_print(" -- "); dbg_bochs_print(cur_task->name); dbg_bochs_print("\n"); //load_pdbr(cur_taskp->pdir); *stack = cur_task->esp; } else { enqueue_task(cur_task->pid, cur_task); } } active = FALSE; return; asm("sti"); } </code></pre> The tss is initalized with the following values: <pre><code>void new_tss(task_register_t* tss, void (*func)()){ tss->eax=0; tss->ebx=0; tss->ecx=0; tss->edx=0; tss->edi =0; tss->esi =0; tss->cs = 8; tss->eip = (unsigned)func; tss->eflags = 0x202; tss->end = (unsigned) suicide; //tss->fine = (unsigned)end; //per metterci il suicide return; } </code></pre> And the function that creates a new task is the following: <pre><code>pid_t new_task(char *task_name, void (*start_function)()){ asm("cli"); task_t *new_task; table_address_t local_table; unsigned int new_pid = request_pid(); new_task = (task_t*)kmalloc(sizeof(task_t)); strcpy(new_task->name, task_name); new_task->next = NULL; new_task->start_function = start_function; new_task->cur_quants=0; new_task->pid = new_pid; new_task->eip = (unsigned int)start_function; new_task->esp = (unsigned int)kmalloc(STACK_SIZE) + STACK_SIZE-100; new_task->status = NEW; new_task->registers = (task_register_t*)new_task->esp; new_tss(new_task->registers, start_function); local_table = map_kernel(); new_task->pdir = local_table.page_dir; new_task->ptable = local_table.page_table; //new_task->pdir = 0; //new_task->ptable = 0; enqueue_task(new_task->pid, new_task); //(task_list.current)->cur_quants = MAX_TICKS; asm("sti"); return new_pid; } </code></pre> I'm sure that i just forgot something, or i miss some consideration. But i cannot figure what i'm missing. Actually i'm working only in kernel mode, and inside the same address space (pagiing is enabled, but actually i use the same pagedir for all tasks). The ISR macros are defined here: <a href="https://github.com/inuyasha82/DreamOs/blob/master/include/processore/handlers.h" rel="nofollow">https://github.com/inuyasha82/DreamOs/blob/master/include/processore/handlers.h</a> I declared four kinds of function in order to handle ISR: <ol> <li>EXCEPTION</li> <li>EXCEPTION_EC (an exception with an error code)</li> <li>IRQ</li> <li>SYSCALL</li> </ol> Obviously the scheduler is called by an IRQ routine, so the macro looks like: <pre><code>__asm__("INT_"#n":"\ "pushad;" \ "movl %esp, %eax;"\ "pushl %eax;"\ "call _irqinterrupt;"\ "popl %eax;"\ "movl %eax, %esp;"\ "popad;"\ "iret;") </code></pre> the irq handler function is: <pre><code>void _irqinterrupt(unsigned int esp){ asm("cli;"); int irqn; irqn = get_current_irq(); IRQ_s* tmpHandler; if(irqn>=0) { tmpHandler = shareHandler[irqn]; if(tmpHandler!=0) { tmpHandler->IRQ_func(); #ifdef DEBUG printf("2 - IRQ_func: %d, %d\n", tmpHandler->IRQ_func, tmpHandler); #endif while(tmpHandler->next!=NULL) { tmpHandler = tmpHandler->next; #ifdef DEBUG printf("1 - IRQ_func (_prova): %d, %d\n", tmpHandler->IRQ_func, tmpHandler); #endif if(tmpHandler!=0) tmpHandler->IRQ_func(); } } else printf("irqn: %d\n", irqn); } else printf("IRQ N: %d E' arrivato qualcosa che non so gestire ", irqn); if(irqn<=8 && irqn!=2) outportb(MASTER_PORT, EOI); else if(irqn<=16 || irqn==2){ outportb(SLAVE_PORT, EOI); outportb(MASTER_PORT, EOI); } schedule(&esp); asm("sti;"); return; } </code></pre> And these are the enqueue_task and dequeue_task functions: <pre><code>void enqueue_task(pid_t pid, task_t* n_task){ n_task->next=NULL; if(task_list.tail == NULL){ task_list.head = n_task; task_list.tail = task_list.head; } else { task_list.head->next=n_task; task_list.head = n_task; } } task_t* dequeue_task(){ if(task_list.head==NULL){ return NULL; } else { task_t* _task; _task = task_list.tail; task_list.tail=_task->next; return _task; } return; } </code></pre> Thanks in advance, and let me know if you need more details!
Tags
<c><scheduling><multitasking><osdev>
Title
Task switching using a queue
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1. This table or related slice is empty.
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 POTask switching using a queue
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