Commit 6c694c88 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: move migration destination verification out of cgroup_migrate_prepare_dst() 



cgroup_migrate_prepare_dst() verifies whether the destination cgroup
is allowable; however, the test doesn't really belong there.  It's too
deep and common in the stack and as a result the test itself is gated
by another test.

Separate the test out into cgroup_may_migrate_to() and update
cgroup_attach_task() and cgroup_transfer_tasks() to perform the test
directly.  This doesn't cause any behavior differences.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 58cdb1ce

kernel/cgroup.c

+20 −8
Original line number Diff line number Diff line
@@ -2443,6 +2443,20 @@ out_release_tset: 
	return ret;

}



/**

 * cgroup_may_migrate_to - verify whether a cgroup can be migration destination

 * @dst_cgrp: destination cgroup to test

 *

 * On the default hierarchy, except for the root, subtree_control must be

 * zero for migration destination cgroups with tasks so that child cgroups

 * don't compete against tasks.

 */

static bool cgroup_may_migrate_to(struct cgroup *dst_cgrp)

{

	return !cgroup_on_dfl(dst_cgrp) || !cgroup_parent(dst_cgrp) ||

		!dst_cgrp->subtree_control;

}



/**

 * cgroup_migrate_finish - cleanup after attach

 * @preloaded_csets: list of preloaded css_sets
@@ -2529,14 +2543,6 @@ static int cgroup_migrate_prepare_dst(struct cgroup *dst_cgrp, 


	lockdep_assert_held(&cgroup_mutex);



	/*

	 * Except for the root, subtree_control must be zero for a cgroup

	 * with tasks so that child cgroups don't compete against tasks.

	 */

	if (dst_cgrp && cgroup_on_dfl(dst_cgrp) && cgroup_parent(dst_cgrp) &&

	    dst_cgrp->subtree_control)

		return -EBUSY;



	/* look up the dst cset for each src cset and link it to src */

	list_for_each_entry_safe(src_cset, tmp_cset, preloaded_csets, mg_preload_node) {

		struct css_set *dst_cset;
@@ -2634,6 +2640,9 @@ static int cgroup_attach_task(struct cgroup *dst_cgrp, 
	struct task_struct *task;

	int ret;



	if (!cgroup_may_migrate_to(dst_cgrp))

		return -EBUSY;



	/* look up all src csets */

	spin_lock_bh(&css_set_lock);

	rcu_read_lock();
@@ -4136,6 +4145,9 @@ int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from) 
	struct task_struct *task;

	int ret;



	if (!cgroup_may_migrate_to(to))

		return -EBUSY;



	mutex_lock(&cgroup_mutex);



	/* all tasks in @from are being moved, all csets are source */

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