Messages in this thread | | | Date | Tue, 21 Aug 2012 20:27:51 +0200 | From | Oleg Nesterov <> | Subject | Re: lockdep trace from posix timers |
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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... } }
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