Re: tasklet_action() failure

[Mohammad M Molla <merajul_i@xxxxxxxxx>]

asklet_action is called for handling tasklets that have already been scheduled. So for these tasklets t->state should have TASKLET_STATE_SCHED bit set.

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

----- Original Message ----
From: Tony Mouawad <tonym.ace@xxxxxxxxx>
To: kernelnewbies <kernelnewbies@xxxxxxxxxxxx>
Sent: Monday, October 22, 2007 5:19:05 PM
Subject: tasklet_action() failure

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 }

--
To unsubscribe from this list: send an email with
"unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx
Please read the FAQ at http://kernelnewbies.org/FAQ

__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com