On 08/20, Oleg Nesterov wrote:
>
> On 08/20, Peter Zijlstra wrote:
> >
> > Anyway, would taking ->pi_lock over _cancel and _run suffice?
>
> I thinks yes... But I can't think properly today.
OK, how about the code below?
Oleg.
#define TWORK_EXITED ((struct callback_head*)1)
static inline bool cmp_xchg(struct callback_head **ptr, void *old, void *new)
{
return cmpxchg(ptr, old, new) == old;
}
int
task_work_add(struct task_struct *task, struct callback_head *twork, bool
notify)
{
do {
twork->next = ACCESS_ONCE(task->task_works);
if (unlikely(twork->next == TWORK_EXITED))
return -ESRCH;
} while (cmp_xchg(&task->task_works, twork->next, twork));
/* test_and_set_bit() implies mb(), see tracehook_notify_resume(). */
if (notify)
set_notify_resume(task);
return 0;
}
struct callback_head *
task_work_cancel(struct task_struct *task, task_work_func_t func)
{
struct callback_head *twork = NULL, **pprev = &task->task_works;
unsigned long flags;
raw_spin_lock_irqsave(&task->pi_lock, flags);
if (likely(*pprev != TWORK_EXITED)) {
for (; (twork = *pprev); pprev = &twork) {
read_barrier_depends();
if (twork->func != func)
continue;
while (!cmp_xchg(pprev, twork, twork->next))
// COMMENT ABOUT THE RACE WITH _add()
pprev = &(*pprev)->next;
break;
}
}
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
return twork;
}
void task_work_run(void)
{
struct task_struct *task = current;
struct callback_head *twork, *marker;
for (;;) {
raw_spin_lock_irq(&task->pi_lock);
do {
twork = ACCESS_ONCE(task->task_works);
marker = (!twork && (task->flags & PF_EXITING)) ?
TWORK_EXITED : NULL;
} while (cmp_xchg(&task->task_works, twork, marker));
raw_spin_unlock_irq(&task->pi_lock);
if (!twork)
break;
...run works...
}
}
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
