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Commit 04502365 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: remove cgroup_pidlist->use_count 



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: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent 4bac00d1

kernel/cgroup.c

+7 −21
Original line number Original line Diff line number Diff line
@@ -3456,8 +3456,6 @@ struct cgroup_pidlist { 
	pid_t *list;

	pid_t *list;

	/* how many elements the above list has */

	/* how many elements the above list has */

	int length;

	int length;

	/* how many files are using the current array */

	int use_count;

	/* each of these stored in a list by its cgroup */

	/* each of these stored in a list by its cgroup */

	struct list_head links;

	struct list_head links;

	/* pointer to the cgroup we belong to, for list removal purposes */

	/* pointer to the cgroup we belong to, for list removal purposes */
@@ -3473,8 +3471,6 @@ struct cgroup_pidlist_open_file { 
	struct cgroup_pidlist		*pidlist;

	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

 * 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.

 * 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);

	mutex_lock(&l->owner->pidlist_mutex);





	/*

	/*

	 * Destroy iff we didn't race with a new user or get queued again.

	 * Destroy iff we didn't get queued again.  The state won't change

	 * Queued state won't change as it can only be queued while locked.

	 * 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);

		list_del(&l->links);

		pidlist_free(l->list);

		pidlist_free(l->list);

		put_pid_ns(l->key.ns);

		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);

			return ERR_PTR(ret);

	}

	}

	l = of->pidlist;

	l = of->pidlist;

	l->use_count++;





	if (pid) {

	if (pid) {

		int end = l->length;

		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;

	struct cgroup_pidlist_open_file *of = s->private;





	mutex_unlock(&of->cgrp->pidlist_mutex);

	if (of->pidlist)

	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)

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,

	.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 = {

static const struct file_operations cgroup_pidlist_operations = {

	.read = seq_read,

	.read = seq_read,

	.llseek = seq_lseek,

	.llseek = seq_lseek,