From edae0c3358947f8be5ca99f762d89e0c38e1f5d5 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Tue, 13 Aug 2013 20:22:51 -0400 Subject: cgroup: factor out kill_css() Factor out css ref killing from cgroup_destroy_locked() into kill_css(). We're gonna add more to the path and the factored out function will eventually be called from other places too. While at it, replace open coded percpu_ref_get() with css_get() for consistency. This shouldn't cause any functional difference as the function is not used for root cgroups. Signed-off-by: Tejun Heo Acked-by: Li Zefan --- kernel/cgroup.c | 58 ++++++++++++++++++++++++++++++++++----------------------- 1 file changed, 35 insertions(+), 23 deletions(-) (limited to 'kernel/cgroup.c') diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 3c4c4b01ffe..7b7575f3119 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -4595,6 +4595,36 @@ static void css_killed_ref_fn(struct percpu_ref *ref) schedule_work(&css->destroy_work); } +/** + * kill_css - destroy a css + * @css: css to destroy + * + * This function initiates destruction of @css by putting its base + * reference. ->css_offline() will be invoked asynchronously once + * css_tryget() is guaranteed to fail and when the reference count reaches + * zero, @css will be released. + */ +static void kill_css(struct cgroup_subsys_state *css) +{ + /* + * Killing would put the base ref, but we need to keep it alive + * until after ->css_offline(). + */ + css_get(css); + + /* + * cgroup core guarantees that, by the time ->css_offline() is + * invoked, no new css reference will be given out via + * css_tryget(). We can't simply call percpu_ref_kill() and + * proceed to offlining css's because percpu_ref_kill() doesn't + * guarantee that the ref is seen as killed on all CPUs on return. + * + * Use percpu_ref_kill_and_confirm() to get notifications as each + * css is confirmed to be seen as killed on all CPUs. + */ + percpu_ref_kill_and_confirm(&css->refcnt, css_killed_ref_fn); +} + /** * cgroup_destroy_locked - the first stage of cgroup destruction * @cgrp: cgroup to be destroyed @@ -4641,30 +4671,12 @@ static int cgroup_destroy_locked(struct cgroup *cgrp) return -EBUSY; /* - * Block new css_tryget() by killing css refcnts. cgroup core - * guarantees that, by the time ->css_offline() is invoked, no new - * css reference will be given out via css_tryget(). We can't - * simply call percpu_ref_kill() and proceed to offlining css's - * because percpu_ref_kill() doesn't guarantee that the ref is seen - * as killed on all CPUs on return. - * - * Use percpu_ref_kill_and_confirm() to get notifications as each - * css is confirmed to be seen as killed on all CPUs. - * cgroup_destroy_css_killed() will be invoked to perform the rest - * of destruction once the percpu refs of all css's are confirmed - * to be killed. + * Initiate massacre of all css's. cgroup_destroy_css_killed() + * will be invoked to perform the rest of destruction once the + * percpu refs of all css's are confirmed to be killed. */ - for_each_root_subsys(cgrp->root, ss) { - struct cgroup_subsys_state *css = cgroup_css(cgrp, ss->subsys_id); - - /* - * Killing would put the base ref, but we need to keep it - * alive until after ->css_offline. - */ - percpu_ref_get(&css->refcnt); - - percpu_ref_kill_and_confirm(&css->refcnt, css_killed_ref_fn); - } + for_each_root_subsys(cgrp->root, ss) + kill_css(cgroup_css(cgrp, ss->subsys_id)); /* * Mark @cgrp dead. This prevents further task migration and child -- cgit v1.2.3