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cgroup: make sure a parent css isn't offlined before its children 

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>
Cc: stable@vger.kernel.org
hifive-unleashed-5.1
Tejun Heo 2016-01-21 15:31:11 -05:00
parent e93ad19d05
commit aa226ff4a1
2 changed files with 23 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
include/linux/cgroup-defs.h
View File

@ -127,6 +127,12 @@ struct cgroup_subsys_state {
*/ */
u64 serial_nr; 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 */ /* percpu_ref killing and RCU release */
struct rcu_head rcu_head; struct rcu_head rcu_head;
struct work_struct destroy_work; struct work_struct destroy_work;

22
kernel/cgroup.c
View File

@ -4760,6 +4760,7 @@ static void init_and_link_css(struct cgroup_subsys_state *css,
INIT_LIST_HEAD(&css->sibling); INIT_LIST_HEAD(&css->sibling);
INIT_LIST_HEAD(&css->children); INIT_LIST_HEAD(&css->children);
css->serial_nr = css_serial_nr_next++; css->serial_nr = css_serial_nr_next++;
atomic_set(&css->online_cnt, 0);
if (cgroup_parent(cgrp)) { if (cgroup_parent(cgrp)) {
css->parent = cgroup_css(cgroup_parent(cgrp), ss); css->parent = cgroup_css(cgroup_parent(cgrp), ss);
@ -4782,6 +4783,10 @@ static int online_css(struct cgroup_subsys_state *css)
if (!ret) { if (!ret) {
css->flags |= CSS_ONLINE; css->flags |= CSS_ONLINE;
rcu_assign_pointer(css->cgroup->subsys[ss->id], css); 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; return ret;
} }
@ -5019,10 +5024,15 @@ static void css_killed_work_fn(struct work_struct *work)
container_of(work, struct cgroup_subsys_state, destroy_work); container_of(work, struct cgroup_subsys_state, destroy_work);
mutex_lock(&cgroup_mutex); 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 */ /* css kill confirmation processing requires process context, bounce */
@ -5031,8 +5041,10 @@ static void css_killed_ref_fn(struct percpu_ref *ref)
struct cgroup_subsys_state *css = struct cgroup_subsys_state *css =
container_of(ref, struct cgroup_subsys_state, refcnt); container_of(ref, struct cgroup_subsys_state, refcnt);
INIT_WORK(&css->destroy_work, css_killed_work_fn); if (atomic_dec_and_test(&css->online_cnt)) {
queue_work(cgroup_destroy_wq, &css->destroy_work); INIT_WORK(&css->destroy_work, css_killed_work_fn);
queue_work(cgroup_destroy_wq, &css->destroy_work);
}
} }
/** /**