From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [PATCH 1/8] cgroup: kill cgroup_subsys->__DEPRECATED_clear_css_refs Date: Wed, 31 Oct 2012 09:38:48 -0700 Message-ID: <20121031163848.GC2945@htj.dyndns.org> References: <1351657365-25055-1-git-send-email-tj@kernel.org> <1351657365-25055-2-git-send-email-tj@kernel.org> <509125D9.8070100@parallels.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <509125D9.8070100-bzQdu9zFT3WakBO8gow8eQ@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: Glauber Costa Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, mhocko-AlSwsSmVLrQ@public.gmane.org, hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org List-Id: containers.vger.kernel.org Hello, Glauber. On Wed, Oct 31, 2012 at 05:21:29PM +0400, Glauber Costa wrote: > > + > > + local_irq_disable(); > > + > > + /* block new css_tryget() by deactivating refcnt */ > > + for_each_subsys(cgrp->root, ss) { > > + struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id]; > > + > > + WARN_ON(atomic_read(&css->refcnt) < 0); > > + atomic_add(CSS_DEACT_BIAS, &css->refcnt); > > } > > - /* NO css_tryget() can success after here. */ > > + > > + /* > > + * Set REMOVED. All in-progress css_tryget() will be released. > > + * Put all the base refs. Each css holds an extra reference to the > > + * cgroup's dentry and cgroup removal proceeds regardless of css > > + * refs. On the last put of each css, whenever that may be, the > > + * extra dentry ref is put so that dentry destruction happens only > > + * after all css's are released. > > + */ > > + for_each_subsys(cgrp->root, ss) { > > + struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id]; > > + > > + set_bit(CSS_REMOVED, &css->flags); > > + css_put(css); > > + } > > + > > + local_irq_enable(); > > + > > finish_wait(&cgroup_rmdir_waitq, &wait); > > It seems to me that the main reason for doing this in two passes was to > derive a global "failed" state on the first pass. Now that we can't > fail, why can't you just loop through the subsystems just once ? Later in the series, pre_destroy() happens inbetween. The first loop marks the CSSes and cgrp dead, ->pre_destroy()s are called, and the later loop will put the final ref. I'll mention it in the commit message. Thanks. -- tejun