Messages in this thread | | | Date | Fri, 24 Aug 2012 20:56:19 +0200 | From | Oleg Nesterov <> | Subject | Re: lockdep trace from posix timers |
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On 08/21, Oleg Nesterov wrote: > > > 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)); > ^^^^^^^^^^^^^^^ > > while (!cmp_xchg(...))
and _cancel can be simplified a bit.
OK, I actually tested the code below, seems to work.
Peter, if you think it can work for you and if you agree with the implementation I will be happy to send the patch.
The only change outside of task_work.c is that exit_task_work() should call task_work_run() unconditionally.
As for cmp_xchg below... Of course it is not strictly needed. But otoh, personally I'd like to have this helper (probably renamed) somewhere in include/linux. Perhaps this is just me, but cmpxchg() always confuses me, and most users only need success_or_not from cmpxchg.
Oleg.
#define cmp_xchg(ptr, _old, new) \ ({ \ __typeof__(_old) old = (_old); \ cmpxchg(ptr, old, new) == old; \ })
#define TWORK_EXITED ((struct callback_head*)1)
int task_work_add(struct task_struct *task, struct callback_head *work, bool notify) { do { work->next = ACCESS_ONCE(task->task_works); if (unlikely(work->next == TWORK_EXITED)) return -ESRCH; } while (!cmp_xchg(&task->task_works, work->next, work));
/* 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 **pprev = &task->task_works; struct callback_head *work = NULL; unsigned long flags;
raw_spin_lock_irqsave(&task->pi_lock, flags); if (likely(*pprev != TWORK_EXITED)) { while ((work = *pprev)) { read_barrier_depends(); if (work->func != func) pprev = &work->next; else if (cmp_xchg(pprev, work, work->next)) 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 (;;) { raw_spin_lock_irq(&task->pi_lock); do { work = ACCESS_ONCE(task->task_works); head = !work && (task->flags & PF_EXITING) ? TWORK_EXITED : NULL; } while (!cmp_xchg(&task->task_works, work, head)); raw_spin_unlock_irq(&task->pi_lock);
if (!work) break;
#if PETERZ_WONT_ARGUE_AGAINST_FIFO_TOO_MUCH head = NULL; do { next = work->next; work->next = head; head = work; work = next; } while (work);
work = head; #endif do { next = work->next; work->func(work); work = next; cond_resched(); } while (work); } }
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