Drivers or other kernel subsystems may allow subsystem-specific policy and
configuration to be applied to cgroups. If these subsystems track private data
on a per-cgroup basis, they need a way to be notified about cgroup destruction
so that they can clean up their own internal data for that cgroup. Let's add a
blocking_notifier that will be called whenever a cgroup in the v2 hierarchy is
destroyed to allow this cleanup.
I'm arbitrarily restricting this behavior to the default (cgroup-v2) hierarchy
for now since I don't anticipate it being terribly useful on the legacy
hierarchies. We can certainly relax that restriction if someone comes up with
a use case that needs this on the v1 hierarchies.
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: cgroups@xxxxxxxxxxxxxxx
Signed-off-by: Matt Roper <matthew.d.roper@xxxxxxxxx>
---
include/linux/cgroup.h | 3 +++
kernel/cgroup/cgroup.c | 18 ++++++++++++++++++
2 files changed, 21 insertions(+)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 473e0c0abb86..c9896027ed99 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -43,6 +43,9 @@
/* walk all threaded css_sets in the domain */
#define CSS_TASK_ITER_THREADED (1U << 1)
+/* Driver-registered callbacks for cgroup destruction */
+extern struct blocking_notifier_head cgroup_destroy_notifier_list;
+
/* a css_task_iter should be treated as an opaque object */
struct css_task_iter {
struct cgroup_subsys *ss;
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 2cf06c274e4c..f12c32c6ec7f 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -75,6 +75,15 @@
DEFINE_MUTEX(cgroup_mutex);
DEFINE_SPINLOCK(css_set_lock);
+/*
+ * Driver-registered callbacks for cgroup destruction. Drivers may wish to
+ * track their own per-cgroup data. Registering a callback on this list will
+ * allow them to detect cgroup destruction and perform any appropriate cleanup
+ * of that data when the cgroup is destroyed.
+ */
+BLOCKING_NOTIFIER_HEAD(cgroup_destroy_notifier_list);
+EXPORT_SYMBOL_GPL(cgroup_destroy_notifier_list);
+
#ifdef CONFIG_PROVE_RCU
EXPORT_SYMBOL_GPL(cgroup_mutex);
EXPORT_SYMBOL_GPL(css_set_lock);
@@ -5086,6 +5095,15 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
for_each_css(css, ssid, cgrp)
kill_css(css);
+ /*
+ * Notify listeners of cgroup destruction on the default hierarchy.
+ * Drivers that store per-cgroup data may register for callback to know
+ * when it's safe to reap that data.
+ */
+ if (cgroup_on_dfl(cgrp))
+ blocking_notifier_call_chain(&cgroup_destroy_notifier_list,
+ 0, cgrp);
+
/*
* Remove @cgrp directory along with the base files. @cgrp has an
* extra ref on its kn.
--
2.14.3
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