In line 404, test_and_clear_bit clears TASKLET_STATE_SCHED bit and returns the old value of that bit. If it returns 0, that means a bug, so it calls BUG() handler. Otherwise it skips line 405 and calls tasklet handler.
- Meraj
Tony Mouawad <tonym.ace@xxxxxxxxx> wrote:
Hello,
I'm trying to get a handle on a problem that is occuring inside of a
call to tasklet_action(). Can someone explain a bit about what line
404 is doing ( and the function itself ) in the following code? It
seems that the OS is intermittently resulting in a false result on
line 404 and then executing line 405 which ultimately halts the
kernel.
Regards,
Tony
388 static void tasklet_action(struct softirq_action *a)
389 {
390 struct tasklet_struct *list;
391
392 local_irq_disable();
393 list = __get_cpu_var(tasklet_vec).list;
394 __get_cpu_var(tasklet_vec).list = NULL;
395 local_irq_enable();
396
397 while (list) {
398 struct tasklet_struct *t = list;
399
400 list = list->next;
401
402 if (tasklet_trylock(t)) {
403 if (!atomic_read(&t->count)) {
404 if
(!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))
405 BUG();
406 t->func(t->data);
407 tasklet_unlock(t);
408 continue;
409 }
410 tasklet_unlock(t);
411 }
412
413 local_irq_disable();
414 t->next = __get_cpu_var(tasklet_vec).list;
415 __get_cpu_var(tasklet_vec).list = t;
416 __raise_softirq_irqoff(TASKLET_SOFTIRQ);
417 local_irq_enable();
418 }
419 }
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