From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Denis V. Lunev" Subject: Re: cleanup in workq and dst_destroy Date: Mon, 19 Nov 2007 11:58:04 +0300 Message-ID: <4741501C.1090002@sw.ru> References: <473DC604.9070601@fr.ibm.com> <473DCE16.8020809@sw.ru> <47414D64.9040304@fr.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <47414D64.9040304-NmTC/0ZBporQT0dZR+AlfA@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Daniel Lezcano Cc: Linux Containers , "Denis V. Lunev" , Benjamin Thery , "Eric W. Biederman" , Pavel Emelianov List-Id: containers.vger.kernel.org Daniel Lezcano wrote: > Denis V. Lunev wrote: >> Daniel Lezcano wrote: >>> Hi all, >>> >>> while doing ipv6 namespace, we were faced to a problem with the loopback >>> and the dst_destroy function. >>> >>> When the network namespace exits, the cleanup function is called by >>> schedule_work and this function will browse the net ops list to call the >>> different exit methods for the registered subsystems. >>> >>> The different subsystems will shutdown their resources and in particular >>> addrconf subsystem will ifdown the loopback. This function will call >>> rt6_ifdown >>> -> fib6_clean_all >>> -> fib6_clean_node >>> -> fib6_clean_tree >>> -> fib6_clean_node >>> -> fib6_del >>> -> fib6_del_route >>> -> rt6_release >>> ->dst_free >>> -> __dst_free >>> >>> The __dst_free function will schedule_delayed_work the dst_gc_work >>> function. >>> >>> The dst_gc_work will call dst_destroy and finally this one will call >>> dst->ops->destroy ops function which is ip6_dst_destroy. >>> >>> The problem here is we have the workq blocked because we are running >>> inside the netns cleanup function. So the delayed work will not run >>> until we exits the cleanup function. But the loopback is still >>> referenced by the ip6 routes, the netdev_unregister will loop >>> indefinitly => dead lock. >>> >>> By the way, this bug appears with ipv6 but it is perhaps pending with >>> ipv4. >>> >>> Benjamin as proposed to create a separate workq for the network >>> namespace, so in the worst case we have the unregister looping until the >>> ip6 route are shut downed. Is it an acceptable solution ? >>> >> >> we are doing this staff in the special thread. There are a lot of >> difficult things to perform like synchronize_net & netdev_run_todo inside > > The special thread ? do you mean keventd_wq ? > I mean that network namespace deletion, i.e. all subsystem ->exit calls should be run outside of all current mechanisms in the separate thread, specially designated to namespace(s) stop.