On Sun, Jun 28, 2009 at 12:28:19PM -0400, Gregory Haskins wrote: > Michael S. Tsirkin wrote: > > On Sun, Jun 28, 2009 at 03:57:30PM +0300, Michael S. Tsirkin wrote: > > > >> On Sun, Jun 28, 2009 at 03:56:12PM +0300, Michael S. Tsirkin wrote: > >> > >>> On Sun, Jun 28, 2009 at 08:53:22AM -0400, Gregory Haskins wrote: > >>> > >>>> Michael S. Tsirkin wrote: > >>>> > >>>>> On Thu, Jun 25, 2009 at 09:28:27AM -0400, Gregory Haskins wrote: > >>>>> > >>>>> > >>>>>> eventfd currently emits a POLLHUP wakeup on f_ops->release() to generate a > >>>>>> "release" callback. This lets eventfd clients know if the eventfd is about > >>>>>> to go away and is very useful particularly for in-kernel clients. However, > >>>>>> until recently it is not possible to use this feature of eventfd in a > >>>>>> race-free way. This patch utilizes a new eventfd interface to rectify > >>>>>> the problem. > >>>>>> > >>>>>> Note that one final race is known to exist: the slow-work thread may race > >>>>>> with module removal. We are currently working with slow-work upstream > >>>>>> to fix this issue as well. Since the code prior to this patch also > >>>>>> races with module_put(), we are not making anything worse, but rather > >>>>>> shifting the cause of the race. Once the slow-work code is patched we > >>>>>> will be fixing the last remaining issue. > >>>>>> > >>>>>> > >>>>> By the way, why are we using slow-work here? Wouldn't a regular > >>>>> workqueue do just as well, with less code, and avoid the race? > >>>>> > >>>>> > >>>>> > >>>> I believe it will cause a problem if you do a "flush_work()" from inside > >>>> a work-item. I could be wrong, of course, but it looks like a recipe to > >>>> deadlock. > >>>> > >>>> -Greg > >>>> > >>>> > >>> Sure, but the idea is to only flush on kvm close, never from work item. > >>> > >> To clarify, you don't flush slow works from a work-item, > >> so you shouldn't need to flush workqueue either. > >> > > > > I guess my question is - why is slow work different? It's still > > a thread pool underneath ... > > > > > Its not interdependent. Flush-work blocks the thread..if the thread > happens to be the work-queue thread you may deadlock preventing it from > processing further jobs like the inject. In reality it shouldnt be > possible, but its just a bad idea to assume its ok. > Slow work, on the > other hand, will just make a new thread. > > -Greg > But if you create your own workqueue, and all you do there is destroy irqfds, things are ok I think. Right? -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
