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cgroup: move migration destination verification out of cgroup_migrate_prepare_dst()

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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: Tejun Heo <tj@kernel.org>
This commit is contained in:
Tejun Heo 2016-03-08 11:51:25 -05:00
parent 58cdb1ceb1
commit 6c694c8825
1 changed files with 20 additions and 8 deletions
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28
kernel/cgroup.c
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@ -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 */