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
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