path: root/kernel/cgroup.c
diff options
authorTejun Heo <>2016-03-08 11:51:26 -0500
committerTejun Heo <>2016-03-08 11:51:26 -0500
commite4857982f49d21c05a84351b56724bf353022355 (patch)
treedc2e6039b714635e36ab148ed1ef20a9cbb01f4a /kernel/cgroup.c
parent37ff9f8f474216d0cfca7565a4e0caa521ee6e7e (diff)
cgroup: use css_set->mg_dst_cgrp for the migration target cgroup
Migration can be multi-target on the default hierarchy when a controller is enabled - processes belonging to each child cgroup have to be moved to the child cgroup itself to refresh css association. This isn't a problem for cgroup_migrate_add_src() as each source css_set still maps to single source and target cgroups; however, cgroup_migrate_prepare_dst() is called once after all source css_sets are added and thus might not have a single destination cgroup. This is currently worked around by specifying NULL for @dst_cgrp and using the source's default cgroup as destination as the only multi-target migration in use is self-targetting. While this works, it's subtle and clunky. As all taget cgroups are already specified while preparing the source css_sets, this clunkiness can easily be removed by recording the target cgroup in each source css_set. This patch adds css_set->mg_dst_cgrp which is recorded on cgroup_migrate_src() and used by cgroup_migrate_prepare_dst(). This also makes migration code ready for arbitrary multi-target migration. Signed-off-by: Tejun Heo <>
Diffstat (limited to 'kernel/cgroup.c')
1 files changed, 13 insertions, 13 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 5dd761355033..fbd3e99a4e98 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2473,6 +2473,7 @@ static void cgroup_migrate_finish(struct list_head *preloaded_csets)
list_for_each_entry_safe(cset, tmp_cset, preloaded_csets, mg_preload_node) {
cset->mg_src_cgrp = NULL;
+ cset->mg_dst_cgrp = NULL;
cset->mg_dst_cset = NULL;
@@ -2511,32 +2512,31 @@ static void cgroup_migrate_add_src(struct css_set *src_cset,
+ WARN_ON(src_cset->mg_dst_cgrp);
src_cset->mg_src_cgrp = src_cgrp;
+ src_cset->mg_dst_cgrp = dst_cgrp;
list_add(&src_cset->mg_preload_node, preloaded_csets);
* cgroup_migrate_prepare_dst - prepare destination css_sets for migration
- * @dst_cgrp: the destination cgroup (may be %NULL)
* @preloaded_csets: list of preloaded source css_sets
- * Tasks are about to be moved to @dst_cgrp and all the source css_sets
- * have been preloaded to @preloaded_csets. This function looks up and
- * pins all destination css_sets, links each to its source, and append them
- * to @preloaded_csets. If @dst_cgrp is %NULL, the destination of each
- * source css_set is assumed to be its cgroup on the default hierarchy.
+ * Tasks are about to be moved and all the source css_sets have been
+ * preloaded to @preloaded_csets. This function looks up and pins all
+ * destination css_sets, links each to its source, and append them to
+ * @preloaded_csets.
* This function must be called after cgroup_migrate_add_src() has been
* called on each migration source css_set. After migration is performed
* using cgroup_migrate(), cgroup_migrate_finish() must be called on
* @preloaded_csets.
-static int cgroup_migrate_prepare_dst(struct cgroup *dst_cgrp,
- struct list_head *preloaded_csets)
+static int cgroup_migrate_prepare_dst(struct list_head *preloaded_csets)
struct css_set *src_cset, *tmp_cset;
@@ -2547,8 +2547,7 @@ static int cgroup_migrate_prepare_dst(struct cgroup *dst_cgrp,
list_for_each_entry_safe(src_cset, tmp_cset, preloaded_csets, mg_preload_node) {
struct css_set *dst_cset;
- dst_cset = find_css_set(src_cset,
- dst_cgrp ?: src_cset->dfl_cgrp);
+ dst_cset = find_css_set(src_cset, src_cset->mg_dst_cgrp);
if (!dst_cset)
goto err;
@@ -2561,6 +2560,7 @@ static int cgroup_migrate_prepare_dst(struct cgroup *dst_cgrp,
if (src_cset == dst_cset) {
src_cset->mg_src_cgrp = NULL;
+ src_cset->mg_dst_cgrp = NULL;
@@ -2657,7 +2657,7 @@ static int cgroup_attach_task(struct cgroup *dst_cgrp,
/* prepare dst csets and commit */
- ret = cgroup_migrate_prepare_dst(dst_cgrp, &preloaded_csets);
+ ret = cgroup_migrate_prepare_dst(&preloaded_csets);
if (!ret)
ret = cgroup_migrate(leader, threadgroup, dst_cgrp->root);
@@ -2916,7 +2916,7 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp)
/* NULL dst indicates self on default hierarchy */
- ret = cgroup_migrate_prepare_dst(NULL, &preloaded_csets);
+ ret = cgroup_migrate_prepare_dst(&preloaded_csets);
if (ret)
goto out_finish;
@@ -4156,7 +4156,7 @@ int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from)
cgroup_migrate_add_src(link->cset, to, &preloaded_csets);
- ret = cgroup_migrate_prepare_dst(to, &preloaded_csets);
+ ret = cgroup_migrate_prepare_dst(&preloaded_csets);
if (ret)
goto out_err;