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Subjecttasklet_kill will always hang for recursive tasklets on a UP
Hi,
While going thru the code for tasklet_kill(), I cannot figure out
how recursive tasklets (tasklets that schedule themselves from within
their tasklet handler) can be killed by this function. To me it looks that
tasklet_kill will never complete for such tasklets.

void tasklet_kill(struct tasklet_struct *t)
{
...
...
while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
current->state = TASK_RUNNING;
do
sys_sched_yield();
while (test_bit(TASKLET_STATE_SCHED, &t->state));
}
...
...
}

The above while loop will only exit if TASKLET_STATE_SCHED is not set
(tasklet is not scheduled).
Now if we see tasklet_action

static void tasklet_action(struct softirq_action *a)
{
...
...
if (!atomic_read(&t->count)) {
--> TASKLET_STATE_SCHED is set here
if(!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))
BUG();
t->func(t->data);
--> if we schedule the tasklet inside its handler,
--> TASKLET_STATE_SCHED will be set here also
tasklet_unlock(t);
continue;
}
...
...
}

The only small window when TASKLET_STATE_SCHED is not set is between the
time when test_and_clear_bit above clears it and by the time the tasklet
handler again calls tasklet_schedule(). But since tasklet_kill is called
from user context the while loop in tasklet_kill checking for
TASKLET_STATE_SCHED to be cleared cannot interleave between the above two
lines in tasklet_action and hence tasklet_kill will never come out of the
while loop.
This is true only for UP machines.

Pleae point me out if I am missing something.

Thanx
tomar


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