On Thu, 25 Oct 2012 17:08:32 -0700 "Paton J. Lewis" <palewis@xxxxxxxxx> wrote: > It is not currently possible to reliably delete epoll items when using the > same epoll set from multiple threads. After calling epoll_ctl with > EPOLL_CTL_DEL, another thread might still be executing code related to an > event for that epoll item (in response to epoll_wait). Therefore the deleting > thread does not know when it is safe to delete resources pertaining to the > associated epoll item because another thread might be using those resources. > > The deleting thread could wait an arbitrary amount of time after calling > epoll_ctl with EPOLL_CTL_DEL and before deleting the item, but this is > inefficient and could result in the destruction of resources before another > thread is done handling an event returned by epoll_wait. > > This patch enhances epoll_ctl to support EPOLL_CTL_DISABLE, which disables an > epoll item. If epoll_ctl returns -EBUSY in this case, then another thread may > handling a return from epoll_wait for this item. Otherwise if epoll_ctl > returns 0, then it is safe to delete the epoll item. This allows multiple > threads to use a mutex to determine when it is safe to delete an epoll item > and its associated resources, which allows epoll items to be deleted both > efficiently and without error in a multi-threaded environment. Note that > EPOLL_CTL_DISABLE is only useful in conjunction with EPOLLONESHOT, and using > EPOLL_CTL_DISABLE on an epoll item without EPOLLONESHOT returns -EINVAL. > > This patch also adds a new test_epoll self-test program to both demonstrate > the need for this feature and test it. Thanks. I queued this for testing and for consideration for 3.8. I shall send the revert patches in to Linus to remove this interface change from 3.7. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
