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 <tj@kernel.org>
Acked-by: Zefan Li <lizefan@huawei.com>
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 2cb4b54..d295e6a 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2965,6 +2965,53 @@
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 @@
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 @@
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;