Messages in this thread | | | From | Linus Torvalds <> | Date | Sat, 14 Apr 2012 01:00:46 -0700 | Subject | Re: [PATCH v4 1/3] task_work_add: generic process-context callbacks |
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On Fri, Apr 13, 2012 at 8:39 PM, Oleg Nesterov <oleg@redhat.com> wrote: >> >> Alternatively, you must make the rule be that the data can only be >> freed by the caller *if* it was returned from "task_work_cancel()". > > Exactly. > > Once the caller does task_work_add(twork), it no longer "owns" this > twork. > > But, if task_work_cancel() succeeds - you own it again.
*IF* it succeeds.
My argument was that it might race, and not successfully remove the work entry at all - but because it was allocated on the stack, it gets freed *regardless* of whether the cancel got it or not.
>> But then you can't allocate it on the stack any more, and have to >> allocate it separately. > > Yes, unless you do task_work_add/cancel(current).
Ok, your argument seems to be that "current" is special, and can not race, because the work execution is always synchronous with the task it got scheduled on.
I can buy that. But if so, it needs some big honking comment. Maybe the whole "add yourself onto your *own* task work" should be an explicit separate interface.
And that whole "run_task_work()" function should *not* take a "task" pointer, because it would be horribly horribly wrong to ever run it in any context than "current".
Linus
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