On 08/24, Oleg Nesterov wrote:
>
> Peter, if you think it can work for you and if you agree with
> the implementation I will be happy to send the patch.
I think I should try anyway ;)
To simplify the review, I attached the resulting code below.
Changes:
- Comments.
- Not sure this is really better, but task_work_run()
does not need to actually take pi_lock, unlock_wait
is enough.
However, in this case the dummy entry is better than
the fake pointer.
Oleg.
#include <linux/spinlock.h>
#include <linux/task_work.h>
#include <linux/tracehook.h>
static struct callback_head work_exited; /* all we need is ->next == NULL */
int
task_work_add(struct task_struct *task, struct callback_head *work, bool notify)
{
struct callback_head *head;
do {
head = ACCESS_ONCE(task->task_works);
if (unlikely(head == &work_exited))
return -ESRCH;
work->next = head;
} while (cmpxchg(&task->task_works, head, work) != head);
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 **pprev = &task->task_works;
struct callback_head *work = NULL;
unsigned long flags;
/*
* If cmpxchg() fails we continue without updating pprev.
* Either we raced with task_work_add() which added the
* new entry before this work, we will find it again. Or
* we raced with task_work_run(), *pprev == NULL/exited.
*/
raw_spin_lock_irqsave(&task->pi_lock, flags);
while ((work = ACCESS_ONCE(*pprev))) {
read_barrier_depends();
if (work->func != func)
pprev = &work->next;
else if (cmpxchg(pprev, work, work->next) == work)
break;
}
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
return work;
}
void task_work_run(void)
{
struct task_struct *task = current;
struct callback_head *work, *head, *next;
for (;;) {
/*
* work->func() can do task_work_add(), do not set
* work_exited unless the list is empty.
*/
do {
work = ACCESS_ONCE(task->task_works);
head = !work && (task->flags & PF_EXITING) ?
&work_exited : NULL;
} while (cmpxchg(&task->task_works, work, head) != work);
if (!work)
break;
/*
* Synchronize with task_work_cancel(). It can't remove
* the first entry == work, cmpxchg(task_works) should
* fail, but it can play with *work and other entries.
*/
raw_spin_unlock_wait(&task->pi_lock);
smp_mb();
/* Reverse the list to run the works in fifo order */
head = NULL;
do {
next = work->next;
work->next = head;
head = work;
work = next;
} while (work);
work = head;
do {
next = work->next;
work->func(work);
work = next;
cond_resched();
} while (work);
}
}
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