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cgroup: introduce CSS_ONLINE flag and on/offline_css() helpers

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New helpers on/offline_css() respectively wrap ->post_create() and
->pre_destroy() invocations.  online_css() sets CSS_ONLINE after
->post_create() is complete and offline_css() invokes ->pre_destroy()
iff CSS_ONLINE is set and clears it while also handling the temporary
dropping of cgroup_mutex.

This patch doesn't introduce any behavior change at the moment but
will be used to improve cgroup_create() failure path and allow
->post_create() to fail.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
This commit is contained in:
Tejun Heo 2012-11-19 08:13:37 -08:00
parent 42809dd422
commit a31f2d3ff7
2 changed files with 43 additions and 23 deletions
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1
include/linux/cgroup.h
View file

@ -82,6 +82,7 @@ struct cgroup_subsys_state {
/* bits in struct cgroup_subsys_state flags field */
enum {
CSS_ROOT = (1 << 0), /* this CSS is the root of the subsystem */
CSS_ONLINE = (1 << 1), /* between ->post_create() and ->pre_destroy() */
};
/* Caller must verify that the css is not for root cgroup */

65
kernel/cgroup.c
View file

@ -4035,6 +4035,42 @@ static void init_cgroup_css(struct cgroup_subsys_state *css,
INIT_WORK(&css->dput_work, css_dput_fn);
}
/* invoke ->post_create() on a new CSS and mark it online */
static void online_css(struct cgroup_subsys *ss, struct cgroup *cgrp)
{
lockdep_assert_held(&cgroup_mutex);
if (ss->post_create)
ss->post_create(cgrp);
cgrp->subsys[ss->subsys_id]->flags |= CSS_ONLINE;
}
/* if the CSS is online, invoke ->pre_destory() on it and mark it offline */
static void offline_css(struct cgroup_subsys *ss, struct cgroup *cgrp)
__releases(&cgroup_mutex) __acquires(&cgroup_mutex)
{
struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
lockdep_assert_held(&cgroup_mutex);
if (!(css->flags & CSS_ONLINE))
return;
/*
* pre_destroy() should be called with cgroup_mutex unlocked. See
* 3fa59dfbc3 ("cgroup: fix potential deadlock in pre_destroy") for
* details. This temporary unlocking should go away once
* cgroup_mutex is unexported from controllers.
*/
if (ss->pre_destroy) {
mutex_unlock(&cgroup_mutex);
ss->pre_destroy(cgrp);
mutex_lock(&cgroup_mutex);
}
cgrp->subsys[ss->subsys_id]->flags &= ~CSS_ONLINE;
}
/*
* cgroup_create - create a cgroup
* @parent: cgroup that will be parent of the new cgroup
@ -4137,8 +4173,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
dget(dentry);
/* creation succeeded, notify subsystems */
if (ss->post_create)
ss->post_create(cgrp);
online_css(ss, cgrp);
}
err = cgroup_populate_dir(cgrp, true, root->subsys_mask);
@ -4240,18 +4275,9 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
}
set_bit(CGRP_REMOVED, &cgrp->flags);
/*
* Tell subsystems to initate destruction. pre_destroy() should be
* called with cgroup_mutex unlocked. See 3fa59dfbc3 ("cgroup: fix
* potential deadlock in pre_destroy") for details. This temporary
* unlocking should go away once cgroup_mutex is unexported from
* controllers.
*/
mutex_unlock(&cgroup_mutex);
/* tell subsystems to initate destruction */
for_each_subsys(cgrp->root, ss)
if (ss->pre_destroy)
ss->pre_destroy(cgrp);
mutex_lock(&cgroup_mutex);
offline_css(ss, cgrp);
/*
* Put all the base refs. Each css holds an extra reference to the
@ -4354,9 +4380,7 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
BUG_ON(!list_empty(&init_task.tasks));
ss->active = 1;
if (ss->post_create)
ss->post_create(dummytop);
online_css(ss, dummytop);
mutex_unlock(&cgroup_mutex);
@ -4469,9 +4493,7 @@ int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss)
write_unlock(&css_set_lock);
ss->active = 1;
if (ss->post_create)
ss->post_create(dummytop);
online_css(ss, dummytop);
/* success! */
mutex_unlock(&cgroup_mutex);
@ -4501,12 +4523,9 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss)
*/
BUG_ON(ss->root != &rootnode);
/* ->pre_destroy() should be called outside cgroup_mutex for now */
if (ss->pre_destroy)
ss->pre_destroy(dummytop);
mutex_lock(&cgroup_mutex);
offline_css(ss, dummytop);
ss->active = 0;
if (ss->use_id) {