Messages in this thread | | | Subject | Re: lockdep trace from posix timers | From | Peter Zijlstra <> | Date | Tue, 28 Aug 2012 19:28:50 +0200 |
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On Tue, 2012-08-28 at 19:01 +0200, Oleg Nesterov wrote: > > struct callback_head * > > task_work_cancel(struct task_struct *task, task_work_func_t func) > > { > > + struct callback_head **workp, *work; > > + > > +again: > > + workp = &task->task_works; > > + work = *workp; > > + while (work) { > > + if (work->func == func) { > > But you can't dereference this pointer. Without some locking this > can race with another task_work_cancel() or task_work_run(), this > work can be free/unmapped/reused. > > > + if (cmpxchg(workp, work, work->next) == work) > > + return work; > > Or this can race with task_work_cancel(work) + task_work_add(work). > cmpxchg() can succeed even if work->func is already different.
Bah.. you and your races ;-)
Surely we can do this locklessly.. I'll go try harder still.
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