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cgroup: remove cgroup_pidlist->use_count

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After the recent changes, pidlist ref is held only between
cgroup_pidlist_start() and cgroup_pidlist_stop() during which
cgroup->pidlist_mutex is also held.  IOW, the reference count is
redundant now.  While in use, it's always one and pidlist_mutex is
held - holding the mutex has exactly the same protection.

This patch collapses destroy_dwork queueing into cgroup_pidlist_stop()
so that pidlist_mutex is not released inbetween and drops
pidlist->use_count.

This patch shouldn't introduce any behavior changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
This commit is contained in:
Tejun Heo 2013-11-29 10:42:59 -05:00
parent 4bac00d16a
commit 045023658c
1 changed files with 7 additions and 21 deletions
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28
kernel/cgroup.c
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@ -3456,8 +3456,6 @@ struct cgroup_pidlist {
pid_t *list;
/* how many elements the above list has */
int length;
/* how many files are using the current array */
int use_count;
/* each of these stored in a list by its cgroup */
struct list_head links;
/* pointer to the cgroup we belong to, for list removal purposes */
@ -3473,8 +3471,6 @@ struct cgroup_pidlist_open_file {
struct cgroup_pidlist *pidlist;
};
static void cgroup_release_pid_array(struct cgroup_pidlist *l);
/*
* The following two functions "fix" the issue where there are more pids
* than kmalloc will give memory for; in such cases, we use vmalloc/vfree.
@ -3524,10 +3520,10 @@ static void cgroup_pidlist_destroy_work_fn(struct work_struct *work)
mutex_lock(&l->owner->pidlist_mutex);
/*
* Destroy iff we didn't race with a new user or get queued again.
* Queued state won't change as it can only be queued while locked.
* Destroy iff we didn't get queued again. The state won't change
* as destroy_dwork can only be queued while locked.
*/
if (!l->use_count && !delayed_work_pending(dwork)) {
if (!delayed_work_pending(dwork)) {
list_del(&l->links);
pidlist_free(l->list);
put_pid_ns(l->key.ns);
@ -3775,7 +3771,6 @@ static void *cgroup_pidlist_start(struct seq_file *s, loff_t *pos)
return ERR_PTR(ret);
}
l = of->pidlist;
l->use_count++;
if (pid) {
int end = l->length;
@ -3804,9 +3799,11 @@ static void cgroup_pidlist_stop(struct seq_file *s, void *v)
{
struct cgroup_pidlist_open_file *of = s->private;
mutex_unlock(&of->cgrp->pidlist_mutex);
if (of->pidlist)
cgroup_release_pid_array(of->pidlist);
mod_delayed_work(cgroup_pidlist_destroy_wq,
&of->pidlist->destroy_dwork,
CGROUP_PIDLIST_DESTROY_DELAY);
mutex_unlock(&of->cgrp->pidlist_mutex);
}
static void *cgroup_pidlist_next(struct seq_file *s, void *v, loff_t *pos)
@ -3844,17 +3841,6 @@ static const struct seq_operations cgroup_pidlist_seq_operations = {
.show = cgroup_pidlist_show,
};
static void cgroup_release_pid_array(struct cgroup_pidlist *l)
{
mutex_lock(&l->owner->pidlist_mutex);
BUG_ON(!l->use_count);
/* if the last user, arm the destroy work */
if (!--l->use_count)
mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork,
CGROUP_PIDLIST_DESTROY_DELAY);
mutex_unlock(&l->owner->pidlist_mutex);
}
static const struct file_operations cgroup_pidlist_operations = {
.read = seq_read,
.llseek = seq_lseek,