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Commit 21a2d343 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: simplify dynamic cftype addition and removal 



Dynamic cftype addition and removal using cgroup_add/rm_cftypes()
respectively has been quite hairy due to vfs i_mutex.  As i_mutex
nests outside cgroup_mutex, cgroup_mutex has to be released and
regrabbed on each iteration through the hierarchy complicating the
process.  Now that i_mutex is no longer in play, it can be simplified.

* Just holding cgroup_tree_mutex is enough.  No need to meddle with
  cgroup_mutex.

* No reason to play the unlock - relock - check serial_nr dancing.
  Everything can be atomically while holding cgroup_tree_mutex.

* cgroup_cfts_prepare() is replaced with direct locking of
  cgroup_tree_mutex.

* cgroup_cfts_commit() no longer fiddles with locking.  It just
  applies the cftypes change to the existing cgroups in the hierarchy.
  Renamed to cgroup_cfts_apply().

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent 0adb0704

kernel/cgroup.c

+32 −55
Original line number Diff line number Diff line
@@ -2305,46 +2305,19 @@ static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[], 
	return 0;

}



static void cgroup_cfts_prepare(void)

	__acquires(&cgroup_mutex)

{

	/*

	 * Thanks to the entanglement with vfs inode locking, we can't walk

	 * the existing cgroups under cgroup_mutex and create files.

	 * Instead, we use css_for_each_descendant_pre() and drop RCU read

	 * lock before calling cgroup_addrm_files().

	 */

	mutex_lock(&cgroup_tree_mutex);

	mutex_lock(&cgroup_mutex);

}



static int cgroup_cfts_commit(struct cftype *cfts, bool is_add)

	__releases(&cgroup_mutex)

static int cgroup_apply_cftypes(struct cftype *cfts, bool is_add)

{

	LIST_HEAD(pending);

	struct cgroup_subsys *ss = cfts[0].ss;

	struct cgroup *root = &ss->root->top_cgroup;

	struct cgroup *prev = NULL;

	struct cgroup_subsys_state *css;

	u64 update_before;

	int ret = 0;



	mutex_unlock(&cgroup_mutex);

	lockdep_assert_held(&cgroup_tree_mutex);



	/* %NULL @cfts indicates abort and don't bother if @ss isn't attached */

	if (!cfts || ss->root == &cgroup_dummy_root) {

		mutex_unlock(&cgroup_tree_mutex);

	/* don't bother if @ss isn't attached */

	if (ss->root == &cgroup_dummy_root)

		return 0;

	}



	cgroup_get_root(ss->root);



	/*

	 * All cgroups which are created after we drop cgroup_mutex will

	 * have the updated set of files, so we only need to update the

	 * cgroups created before the current @cgroup_serial_nr_next.

	 */

	update_before = cgroup_serial_nr_next;



	/* add/rm files for all cgroups created before */

	css_for_each_descendant_pre(css, cgroup_css(root, ss)) {
@@ -2353,22 +2326,13 @@ static int cgroup_cfts_commit(struct cftype *cfts, bool is_add) 
		if (cgroup_is_dead(cgrp))

			continue;



		cgroup_get(cgrp);

		if (prev)

			cgroup_put(prev);

		prev = cgrp;



		if (cgrp->serial_nr < update_before && !cgroup_is_dead(cgrp)) {

		ret = cgroup_addrm_files(cgrp, cfts, is_add);

			if (is_add)

				kernfs_activate(cgrp->kn);

		}

		if (ret)

			break;

	}

	mutex_unlock(&cgroup_tree_mutex);

	cgroup_put(prev);

	cgroup_put_root(ss->root);



	if (is_add && !ret)

		kernfs_activate(root->kn);

	return ret;

}
@@ -2419,6 +2383,19 @@ static int cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts) 
	return 0;

}



static int cgroup_rm_cftypes_locked(struct cftype *cfts)

{

	lockdep_assert_held(&cgroup_tree_mutex);



	if (!cfts || !cfts[0].ss)

		return -ENOENT;



	list_del(&cfts->node);

	cgroup_apply_cftypes(cfts, false);

	cgroup_exit_cftypes(cfts);

	return 0;

}



/**

 * cgroup_rm_cftypes - remove an array of cftypes from a subsystem

 * @cfts: zero-length name terminated array of cftypes
@@ -2432,15 +2409,12 @@ static int cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts) 
 */

int cgroup_rm_cftypes(struct cftype *cfts)

{

	if (!cfts || !cfts[0].ss)

		return -ENOENT;



	cgroup_cfts_prepare();

	list_del(&cfts->node);

	cgroup_cfts_commit(cfts, false);

	int ret;



	cgroup_exit_cftypes(cfts);

	return 0;

	mutex_lock(&cgroup_tree_mutex);

	ret = cgroup_rm_cftypes_locked(cfts);

	mutex_unlock(&cgroup_tree_mutex);

	return ret;

}



/**
@@ -2465,11 +2439,14 @@ int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts) 
	if (ret)

		return ret;



	cgroup_cfts_prepare();

	mutex_lock(&cgroup_tree_mutex);



	list_add_tail(&cfts->node, &ss->cfts);

	ret = cgroup_cfts_commit(cfts, true);

	ret = cgroup_apply_cftypes(cfts, true);

	if (ret)

		cgroup_rm_cftypes(cfts);

		cgroup_rm_cftypes_locked(cfts);



	mutex_unlock(&cgroup_tree_mutex);

	return ret;

}

EXPORT_SYMBOL_GPL(cgroup_add_cftypes);