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Commit a25eb52e authored by Zefan Li's avatar Zefan Li Committed by Tejun Heo
Browse files

cgroup: remove CGRP_RELEASABLE flag 



We call put_css_set() after setting CGRP_RELEASABLE flag in
cgroup_task_migrate(), but in other places we call it without setting
the flag. I don't see the necessity of this flag.

Moreover once the flag is set, it will never be cleared, unless writing
to the notify_on_release control file, so it can be quite confusing
if we look at the output of debug.releasable.

  # mount -t cgroup -o debug xxx /cgroup
  # mkdir /cgroup/child
  # cat /cgroup/child/debug.releasable
  0   <-- shows 0 though the cgroup is empty
  # echo $$ > /cgroup/child/tasks
  # cat /cgroup/child/debug.releasable
  0
  # echo $$ > /cgroup/tasks && echo $$ > /cgroup/child/tasks
  # cat /proc/child/debug.releasable
  1   <-- shows 1 though the cgroup is not empty

This patch removes the flag, and now debug.releasable shows if the
cgroup is empty or not.

Signed-off-by: default avatarZefan Li <lizefan@huawei.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 4e2ba650

include/linux/cgroup.h

+0 −5
Original line number Diff line number Diff line
@@ -161,11 +161,6 @@ static inline void css_put(struct cgroup_subsys_state *css) 


/* bits in struct cgroup flags field */

enum {

	/*

	 * Control Group has previously had a child cgroup or a task,

	 * but no longer (only if CGRP_NOTIFY_ON_RELEASE is set)

	 */

	CGRP_RELEASABLE,

	/* Control Group requires release notifications to userspace */

	CGRP_NOTIFY_ON_RELEASE,

	/*

kernel/cgroup.c

+13 −27
Original line number Diff line number Diff line
@@ -329,14 +329,6 @@ bool cgroup_is_descendant(struct cgroup *cgrp, struct cgroup *ancestor) 
	return false;

}



static int cgroup_is_releasable(const struct cgroup *cgrp)

{

	const int bits =

		(1 << CGRP_RELEASABLE) |

		(1 << CGRP_NOTIFY_ON_RELEASE);

	return (cgrp->flags & bits) == bits;

}



static int notify_on_release(const struct cgroup *cgrp)

{

	return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
@@ -491,7 +483,7 @@ static unsigned long css_set_hash(struct cgroup_subsys_state *css[]) 
	return key;

}



static void put_css_set_locked(struct css_set *cset, bool taskexit)

static void put_css_set_locked(struct css_set *cset)

{

	struct cgrp_cset_link *link, *tmp_link;

	struct cgroup_subsys *ss;
@@ -517,12 +509,8 @@ static void put_css_set_locked(struct css_set *cset, bool taskexit) 
		/* @cgrp can't go away while we're holding css_set_rwsem */

		if (list_empty(&cgrp->cset_links)) {

			cgroup_update_populated(cgrp, false);

			if (notify_on_release(cgrp)) {

				if (taskexit)

					set_bit(CGRP_RELEASABLE, &cgrp->flags);

			check_for_release(cgrp);

		}

		}



		kfree(link);

	}
@@ -530,7 +518,7 @@ static void put_css_set_locked(struct css_set *cset, bool taskexit) 
	kfree_rcu(cset, rcu_head);

}



static void put_css_set(struct css_set *cset, bool taskexit)

static void put_css_set(struct css_set *cset)

{

	/*

	 * Ensure that the refcount doesn't hit zero while any readers
@@ -541,7 +529,7 @@ static void put_css_set(struct css_set *cset, bool taskexit) 
		return;



	down_write(&css_set_rwsem);

	put_css_set_locked(cset, taskexit);

	put_css_set_locked(cset);

	up_write(&css_set_rwsem);

}
@@ -2037,8 +2025,7 @@ static void cgroup_task_migrate(struct cgroup *old_cgrp, 
	 * task. As trading it for new_cset is protected by cgroup_mutex,

	 * we're safe to drop it here; it will be freed under RCU.

	 */

	set_bit(CGRP_RELEASABLE, &old_cgrp->flags);

	put_css_set_locked(old_cset, false);

	put_css_set_locked(old_cset);

}



/**
@@ -2059,7 +2046,7 @@ static void cgroup_migrate_finish(struct list_head *preloaded_csets) 
		cset->mg_src_cgrp = NULL;

		cset->mg_dst_cset = NULL;

		list_del_init(&cset->mg_preload_node);

		put_css_set_locked(cset, false);

		put_css_set_locked(cset);

	}

	up_write(&css_set_rwsem);

}
@@ -2153,8 +2140,8 @@ static int cgroup_migrate_prepare_dst(struct cgroup *dst_cgrp, 
		if (src_cset == dst_cset) {

			src_cset->mg_src_cgrp = NULL;

			list_del_init(&src_cset->mg_preload_node);

			put_css_set(src_cset, false);

			put_css_set(dst_cset, false);

			put_css_set(src_cset);

			put_css_set(dst_cset);

			continue;

		}
@@ -2163,7 +2150,7 @@ static int cgroup_migrate_prepare_dst(struct cgroup *dst_cgrp, 
		if (list_empty(&dst_cset->mg_preload_node))

			list_add(&dst_cset->mg_preload_node, &csets);

		else

			put_css_set(dst_cset, false);

			put_css_set(dst_cset);

	}



	list_splice_tail(&csets, preloaded_csets);
@@ -4159,7 +4146,6 @@ static u64 cgroup_read_notify_on_release(struct cgroup_subsys_state *css, 
static int cgroup_write_notify_on_release(struct cgroup_subsys_state *css,

					  struct cftype *cft, u64 val)

{

	clear_bit(CGRP_RELEASABLE, &css->cgroup->flags);

	if (val)

		set_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);

	else
@@ -4806,7 +4792,6 @@ static int cgroup_destroy_locked(struct cgroup *cgrp) 
	 */

	kernfs_remove(cgrp->kn);



	set_bit(CGRP_RELEASABLE, &cgroup_parent(cgrp)->flags);

	check_for_release(cgroup_parent(cgrp));



	/* put the base reference */
@@ -5244,12 +5229,12 @@ void cgroup_exit(struct task_struct *tsk) 
	}



	if (put_cset)

		put_css_set(cset, true);

		put_css_set(cset);

}



static void check_for_release(struct cgroup *cgrp)

{

	if (cgroup_is_releasable(cgrp) && !cgroup_has_tasks(cgrp) &&

	if (notify_on_release(cgrp) && !cgroup_has_tasks(cgrp) &&

	    !css_has_online_children(&cgrp->self) && !cgroup_is_dead(cgrp))

		schedule_work(&cgrp->release_agent_work);

}
@@ -5496,7 +5481,8 @@ static int cgroup_css_links_read(struct seq_file *seq, void *v) 


static u64 releasable_read(struct cgroup_subsys_state *css, struct cftype *cft)

{

	return test_bit(CGRP_RELEASABLE, &css->cgroup->flags);

	return (!cgroup_has_tasks(css->cgroup) &&

		!css_has_online_children(&css->cgroup->self));

}



static struct cftype debug_files[] =  {