diff options
| author | Tejun Heo <tj@kernel.org> | 2016-01-21 15:31:11 -0500 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2016-03-03 15:07:28 -0800 |
| commit | 4cbd196324c05809338c7f118b6f374d3c2db7a0 (patch) | |
| tree | d0795b4d2b5f0365b0e3159c5a8a99c16a05a9fc | |
| parent | fff4dc84e72419196623f118312f571a2e057196 (diff) | |
cgroup: make sure a parent css isn't offlined before its children
commit aa226ff4a1ce79f229c6b7a4c0a14e17fececd01 upstream.
There are three subsystem callbacks in css shutdown path -
css_offline(), css_released() and css_free(). Except for
css_released(), cgroup core didn't guarantee the order of invocation.
css_offline() or css_free() could be called on a parent css before its
children. This behavior is unexpected and led to bugs in cpu and
memory controller.
This patch updates offline path so that a parent css is never offlined
before its children. Each css keeps online_cnt which reaches zero iff
itself and all its children are offline and offline_css() is invoked
only after online_cnt reaches zero.
This fixes the memory controller bug and allows the fix for cpu
controller.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-and-tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reported-by: Brian Christiansen <brian.o.christiansen@gmail.com>
Link: http://lkml.kernel.org/g/5698A023.9070703@de.ibm.com
Link: http://lkml.kernel.org/g/CAKB58ikDkzc8REt31WBkD99+hxNzjK4+FBmhkgS+NVrC9vjMSg@mail.gmail.com
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | include/linux/cgroup-defs.h | 6 | ||||
| -rw-r--r-- | kernel/cgroup.c | 22 |
2 files changed, 23 insertions, 5 deletions
diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h index 06b77f9dd3f2..8e30faeab183 100644 --- a/include/linux/cgroup-defs.h +++ b/include/linux/cgroup-defs.h @@ -133,6 +133,12 @@ struct cgroup_subsys_state { */ u64 serial_nr; + /* + * Incremented by online self and children. Used to guarantee that + * parents are not offlined before their children. + */ + atomic_t online_cnt; + /* percpu_ref killing and RCU release */ struct rcu_head rcu_head; struct work_struct destroy_work; diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 0798f7bdfdc4..fb1ecfd2decd 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -4784,6 +4784,7 @@ static void init_and_link_css(struct cgroup_subsys_state *css, INIT_LIST_HEAD(&css->sibling); INIT_LIST_HEAD(&css->children); css->serial_nr = css_serial_nr_next++; + atomic_set(&css->online_cnt, 0); if (cgroup_parent(cgrp)) { css->parent = cgroup_css(cgroup_parent(cgrp), ss); @@ -4806,6 +4807,10 @@ static int online_css(struct cgroup_subsys_state *css) if (!ret) { css->flags |= CSS_ONLINE; rcu_assign_pointer(css->cgroup->subsys[ss->id], css); + + atomic_inc(&css->online_cnt); + if (css->parent) + atomic_inc(&css->parent->online_cnt); } return ret; } @@ -5037,10 +5042,15 @@ static void css_killed_work_fn(struct work_struct *work) container_of(work, struct cgroup_subsys_state, destroy_work); mutex_lock(&cgroup_mutex); - offline_css(css); - mutex_unlock(&cgroup_mutex); - css_put(css); + do { + offline_css(css); + css_put(css); + /* @css can't go away while we're holding cgroup_mutex */ + css = css->parent; + } while (css && atomic_dec_and_test(&css->online_cnt)); + + mutex_unlock(&cgroup_mutex); } /* css kill confirmation processing requires process context, bounce */ @@ -5049,8 +5059,10 @@ static void css_killed_ref_fn(struct percpu_ref *ref) struct cgroup_subsys_state *css = container_of(ref, struct cgroup_subsys_state, refcnt); - INIT_WORK(&css->destroy_work, css_killed_work_fn); - queue_work(cgroup_destroy_wq, &css->destroy_work); + if (atomic_dec_and_test(&css->online_cnt)) { + INIT_WORK(&css->destroy_work, css_killed_work_fn); + queue_work(cgroup_destroy_wq, &css->destroy_work); + } } /** |