On Mon, Jul 16, 2012 at 08:16:34PM +0300, Kirill A. Shutemov wrote: > On Mon, Jul 16, 2012 at 05:53:01PM +0100, Al Viro wrote: > > On Mon, Jul 16, 2012 at 06:09:24PM +0300, Kirill A. Shutemov wrote: > > > From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> > > > > > > On exiting of the last task in a namespace we need to trigger freeing of > > > the namespace. Currently, we call synchronize_rcu() and free_nsproxy() > > > directly on do_exit() path. > > > > > > On my machine synchronize_rcu() blocks for about 0.01 seconds. For > > > comparing: normal exit_group() syscall takes less than 0.0003 seconds. > > > > > > Let's offload synchronize_rcu() and free_nsproxy() to a workqueue. > > > > > > I also move synchronize_rcu() inside free_nsproxy(). It fixes racy > > > put_nsproxy() which calls free_nsproxy() without synchronize_rcu(). > > > I guess it was missed during switch to RCU (see cf7b708). > > > > NAK. Making final umounts of anything in that namespace asynchronous, > > even though nothing is holding the stuff on them busy is simply > > wrong. Note that they can take a _long_ time, so we are talking about > > minutes worth of delay in the worst case. It's user-visible and > > it's a serious potential for trouble. > > Good point. > > Now in worst case we have a process which hang for a few minutes in > exit_group() syscall in D state, right? Why is that any better? > Does it provide better user experience or better accounting or what? "Session that was using that USB stick has still not finished exiting; might be still busy writing stuff there, so better not pull it out yet". _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
