From: Roman Gushchin <guroan@gmail.com>
To: Tejun Heo <tj@kernel.org>, Oleg Nesterov <oleg@redhat.com>
Cc: kernel-team@fb.com, cgroups@vger.kernel.org,
linux-kernel@vger.kernel.org, Roman Gushchin <guro@fb.com>
Subject: [PATCH v8 3/7] cgroup: protect cgroup->nr_(dying_)descendants by css_set_lock
Date: Tue, 19 Feb 2019 14:02:48 -0800 [thread overview]
Message-ID: <20190219220252.4906-4-guro@fb.com> (raw)
In-Reply-To: <20190219220252.4906-1-guro@fb.com>
The number of descendant cgroups and the number of dying
descendant cgroups are currently synchronized using the cgroup_mutex.
The number of descendant cgroups will be required by the cgroup v2
freezer, which will use it to determine if a cgroup is frozen
(depending on total number of descendants and number of frozen
descendants). It's not always acceptable to grab the cgroup_mutex,
especially from quite hot paths (e.g. exit()).
To avoid this, let's additionally synchronize these counters using
the css_set_lock.
So, it's safe to read these counters with either cgroup_mutex or
css_set_lock locked, and for changing both locks should be acquired.
Signed-off-by: Roman Gushchin <guro@fb.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: kernel-team@fb.com
---
include/linux/cgroup-defs.h | 5 +++++
kernel/cgroup/cgroup.c | 6 ++++++
2 files changed, 11 insertions(+)
diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 120d1d40704b..319c07305500 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -348,6 +348,11 @@ struct cgroup {
* Dying cgroups are cgroups which were deleted by a user,
* but are still existing because someone else is holding a reference.
* max_descendants is a maximum allowed number of descent cgroups.
+ *
+ * nr_descendants and nr_dying_descendants are protected
+ * by cgroup_mutex and css_set_lock. It's fine to read them holding
+ * any of cgroup_mutex and css_set_lock; for writing both locks
+ * should be held.
*/
int nr_descendants;
int nr_dying_descendants;
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index b230afccf635..7438c24297d4 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -4758,9 +4758,11 @@ static void css_release_work_fn(struct work_struct *work)
if (cgroup_on_dfl(cgrp))
cgroup_rstat_flush(cgrp);
+ spin_lock_irq(&css_set_lock);
for (tcgrp = cgroup_parent(cgrp); tcgrp;
tcgrp = cgroup_parent(tcgrp))
tcgrp->nr_dying_descendants--;
+ spin_unlock_irq(&css_set_lock);
cgroup_idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
cgrp->id = -1;
@@ -4978,12 +4980,14 @@ static struct cgroup *cgroup_create(struct cgroup *parent)
if (ret)
goto out_psi_free;
+ spin_lock_irq(&css_set_lock);
for (tcgrp = cgrp; tcgrp; tcgrp = cgroup_parent(tcgrp)) {
cgrp->ancestor_ids[tcgrp->level] = tcgrp->id;
if (tcgrp != cgrp)
tcgrp->nr_descendants++;
}
+ spin_unlock_irq(&css_set_lock);
if (notify_on_release(parent))
set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
@@ -5268,10 +5272,12 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
if (parent && cgroup_is_threaded(cgrp))
parent->nr_threaded_children--;
+ spin_lock_irq(&css_set_lock);
for (tcgrp = cgroup_parent(cgrp); tcgrp; tcgrp = cgroup_parent(tcgrp)) {
tcgrp->nr_descendants--;
tcgrp->nr_dying_descendants++;
}
+ spin_unlock_irq(&css_set_lock);
cgroup1_check_for_release(parent);
--
2.20.1
next prev parent reply other threads:[~2019-02-19 22:03 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-19 22:02 [PATCH v8 0/7] freezer for cgroup v2 Roman Gushchin
2019-02-19 22:02 ` [PATCH v8 1/7] cgroup: rename freezer.c into legacy_freezer.c Roman Gushchin
2019-02-19 22:02 ` [PATCH v8 2/7] cgroup: implement __cgroup_task_count() helper Roman Gushchin
2019-02-19 22:02 ` Roman Gushchin [this message]
2019-02-19 22:02 ` [PATCH v8 4/7] cgroup: cgroup v2 freezer Roman Gushchin
2019-02-20 14:42 ` Oleg Nesterov
2019-02-20 22:14 ` Roman Gushchin
2019-02-21 16:44 ` Oleg Nesterov
2019-02-19 22:02 ` [PATCH v8 5/7] kselftests: cgroup: don't fail on cg_kill_all() error in cg_destroy() Roman Gushchin
2019-02-19 22:02 ` [PATCH v8 6/7] kselftests: cgroup: add freezer controller self-tests Roman Gushchin
2019-02-19 22:02 ` [PATCH v8 7/7] cgroup: document cgroup v2 freezer interface Roman Gushchin
2019-02-20 14:37 ` [PATCH v8 0/7] freezer for cgroup v2 Oleg Nesterov
2019-02-20 22:00 ` Roman Gushchin
2019-02-21 16:29 ` Oleg Nesterov
2019-02-21 17:34 ` Tejun Heo
2019-02-22 16:34 ` Oleg Nesterov
2019-02-22 18:17 ` Tejun Heo
2019-02-25 15:57 ` Oleg Nesterov
2019-03-05 17:27 ` Tejun Heo
2019-02-21 22:43 ` Roman Gushchin
2019-02-22 17:04 ` Oleg Nesterov
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