From 1b9b96a12b5433ccc477265111122720ccb4965e Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Thu, 3 Mar 2016 09:57:59 -0500 Subject: [PATCH] cgroup: factor out cgroup_drain_offline() from cgroup_subtree_control_write() Factor out async css offline draining into cgroup_drain_offline(). * Nest subsystem walk inside child walk. The child walk will later be converted to subtree walk which is a bit more expensive. * Relocate the draining above subsystem mask preparation, which doesn't create any behavior differences but helps further refactoring. Signed-off-by: Tejun Heo Acked-by: Zefan Li --- kernel/cgroup.c | 77 +++++++++++++++++++++++++++++++++---------------- 1 file changed, 52 insertions(+), 25 deletions(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 2cb4b5419852..d295e6a91cdc 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -2965,6 +2965,53 @@ out_finish: return ret; } +/** + * cgroup_drain_offline - wait for previously offlined csses to go away + * @cgrp: parent of the target cgroups + * + * Because css offlining is asynchronous, userland may try to re-enable a + * controller while the previous css is still around. This function drains + * the previous css instances of @cgrp's children. + * + * Must be called with cgroup_mutex held. Returns %false if there were no + * dying css instances. Returns %true if there were one or more and this + * function waited. On %true return, cgroup_mutex has been dropped and + * re-acquired inbetween which anything could have happened. The caller + * typically would have to start over. + */ +static bool cgroup_drain_offline(struct cgroup *cgrp) +{ + struct cgroup *dsct; + struct cgroup_subsys *ss; + int ssid; + + lockdep_assert_held(&cgroup_mutex); + + cgroup_for_each_live_child(dsct, cgrp) { + for_each_subsys(ss, ssid) { + struct cgroup_subsys_state *css = cgroup_css(dsct, ss); + DEFINE_WAIT(wait); + + if (!css) + continue; + + cgroup_get(dsct); + prepare_to_wait(&dsct->offline_waitq, &wait, + TASK_UNINTERRUPTIBLE); + + mutex_unlock(&cgroup_mutex); + schedule(); + finish_wait(&dsct->offline_waitq, &wait); + mutex_lock(&cgroup_mutex); + + cgroup_put(dsct); + return true; + } + } + + return false; +} + /* change the enabled child controllers for a cgroup in the default hierarchy */ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of, char *buf, size_t nbytes, @@ -3050,6 +3097,11 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of, goto out_unlock; } + if (cgroup_drain_offline(cgrp)) { + cgroup_kn_unlock(of->kn); + return restart_syscall(); + } + /* * Update subsys masks and calculate what needs to be done. More * subsystems than specified may need to be enabled or disabled @@ -3065,31 +3117,6 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of, enable |= css_enable; disable |= css_disable; - /* - * Because css offlining is asynchronous, userland might try to - * re-enable the same controller while the previous instance is - * still around. In such cases, wait till it's gone using - * offline_waitq. - */ - do_each_subsys_mask(ss, ssid, css_enable) { - cgroup_for_each_live_child(child, cgrp) { - DEFINE_WAIT(wait); - - if (!cgroup_css(child, ss)) - continue; - - cgroup_get(child); - prepare_to_wait(&child->offline_waitq, &wait, - TASK_UNINTERRUPTIBLE); - cgroup_kn_unlock(of->kn); - schedule(); - finish_wait(&child->offline_waitq, &wait); - cgroup_put(child); - - return restart_syscall(); - } - } while_each_subsys_mask(); - cgrp->subtree_control = new_sc; cgrp->subtree_ss_mask = new_ss; -- 2.20.1