From mboxrd@z Thu Jan 1 00:00:00 1970 From: Balbir Singh Subject: Re: Containers: css_put() dilemma Date: Tue, 17 Jul 2007 23:10:59 +0530 Message-ID: <469CFF2B.1080702@linux.vnet.ibm.com> References: <469BBE00.8000709@linux.vnet.ibm.com> <6599ad830707161203o7f148c75p52e77d4be3ace487@mail.gmail.com> <469C2792.6050009@linux.vnet.ibm.com> <6599ad830707161935n69776f1t98292fc9990f4766@mail.gmail.com> <20070717070031.GA22410@linux.vnet.ibm.com> <6599ad830707170018p180cb7dfr53e609fd0b186e30@mail.gmail.com> <469C99D1.7090807@linux.vnet.ibm.com> <6599ad830707170849v11fe8cecs6d172cd38d247e09@mail.gmail.com> Reply-To: balbir@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <6599ad830707170849v11fe8cecs6d172cd38d247e09@mail.gmail.com> Sender: linux-kernel-owner@vger.kernel.org To: =?windows-1252?Q?=22Paul_=28=3F=3F=29_Menage=22?= Cc: dhaval@linux.vnet.ibm.com, Pavel Emelianov , linux kernel mailing list , Paul Jackson , Linux Containers , Andrew Morton List-Id: containers.vger.kernel.org Paul (??) Menage wrote: > Because as soon as you do the atomic_dec_and_test() on css->refcnt and > the refcnt hits zero, then theoretically someone other thread (that > already holds container_mutex) could check that the refcount is zero > and free the container structure. > Hi, Paul, That sounds correct. I wonder now if the solution should be some form of delegation for deletion of unreferenced containers (HINT: work queue or kernel threads). > Adding a synchronize_rcu in container_diput() guarantees that the > container structure won't be freed while someone may still be > accessing it. > Do we take rcu_read_lock() in css_put() path or use call_rcu() to free the container? >> >> Could you please elaborate as to why using a release agent is broken >> when the memory controller is attached to it? > > Because then it will try to take container_mutex in css_put() if it > drops the last reference to a container, which is the thing that you > said you had to avoid since you called css_put() in contexts that > couldn't sleep. > > Paul -- Warm Regards, Balbir Singh Linux Technology Center IBM, ISTL