From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: [PATCH 1/8] cgroup: kill cgroup_subsys->__DEPRECATED_clear_css_refs Date: Wed, 31 Oct 2012 21:08:59 +0100 Message-ID: <20121031200859.GE1271@dhcp22.suse.cz> References: <1351712650-23709-1-git-send-email-tj@kernel.org> <1351712650-23709-2-git-send-email-tj@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <1351712650-23709-2-git-send-email-tj-DgEjT+Ai2ygdnm+yROfE0A@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: Tejun Heo Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@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 On Wed 31-10-12 12:44:03, Tejun Heo wrote: [...] > local_irq_save/restore() from cgroup_clear_css_refs() are replaced > with local_irq_disable/enable() for simplicity. This is safe as > cgroup_rmdir() is always called with IRQ enabled. Note that this IRQ > switching is necessary to make CSS deactivation and CSS_REMOVED > assertion atomic against css_tryget() and will be removed by future > changes. local_irq_disable doesn't guarantee atomicity, because other CPUs will see the change in steps so this is a bit misleading. The real reason AFAICS is that we do not want to hang in css_tryget from IRQ context (does this really happen btw.?) which would interrupt cgroup_rmdir between we add CSS_DEACT_BIAS and the group is marked CGRP_REMOVED. Or am I still missing the point? [...] -- Michal Hocko SUSE Labs