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SubjectRe: lockdep trace from posix timers
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On Mon, 2012-08-20 at 13:44 +0200, Peter Zijlstra wrote:
> int
> +task_work_add(struct task_struct *task, struct callback_head *work, bool notify)
> {
> + struct callback_head **head = &task->task_works;
> + struct callback_head *entry, *old_entry;
> +
> + entry = &head;

My compiler just alerted me that:

entry = *head;
works a lot better..

> + for (;;) {
> + if (entry == &dead)
> + return -ESRCH;
> +
> + old_entry = entry;
> + work->next = entry;
> + entry = cmpxchg(head, old_entry, work);
> + if (entry == old_entry)
> + break;
> + }
>
> /* test_and_set_bit() implies mb(), see tracehook_notify_resume(). */
> if (notify)
> set_notify_resume(task);
> +
> return 0;
> }


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