[PATCH 2/3] cgroup: track migration context in cgroup_mgctx
From: Tejun Heo
Date: Thu Dec 29 2016 - 17:11:40 EST
cgroup migration is performed in four steps - css_set preloading,
addition of target tasks, actual migration, and clean up. A list
named preloaded_csets is used to track the preloading. This is a bit
too restricted and the code is already depending on the subtlety that
all source css_sets appear before destination ones.
Let's create struct cgroup_mgctx which keeps track of everything
during migration. Currently, it has separate preload lists for source
and destination csets and also embeds cgroup_taskset which is used
during the actual migration. This moves struct cgroup_taskset
definition to cgroup-internal.h.
This patch doesn't cause any functional changes.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
kernel/cgroup/cgroup-internal.h | 66 ++++++++++++++++--
kernel/cgroup/cgroup-v1.c | 10 +--
kernel/cgroup/cgroup.c | 144 ++++++++++++++++------------------------
3 files changed, 122 insertions(+), 98 deletions(-)
diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h
index 589b0e7..5f8c8ac 100644
--- a/kernel/cgroup/cgroup-internal.h
+++ b/kernel/cgroup/cgroup-internal.h
@@ -26,6 +26,61 @@ struct cgrp_cset_link {
struct list_head cgrp_link;
};
+/* used to track tasks and csets during migration */
+struct cgroup_taskset {
+ /* the src and dst cset list running through cset->mg_node */
+ struct list_head src_csets;
+ struct list_head dst_csets;
+
+ /* the subsys currently being processed */
+ int ssid;
+
+ /*
+ * Fields for cgroup_taskset_*() iteration.
+ *
+ * Before migration is committed, the target migration tasks are on
+ * ->mg_tasks of the csets on ->src_csets. After, on ->mg_tasks of
+ * the csets on ->dst_csets. ->csets point to either ->src_csets
+ * or ->dst_csets depending on whether migration is committed.
+ *
+ * ->cur_csets and ->cur_task point to the current task position
+ * during iteration.
+ */
+ struct list_head *csets;
+ struct css_set *cur_cset;
+ struct task_struct *cur_task;
+};
+
+/* migration context also tracks preloading */
+struct cgroup_mgctx {
+ /*
+ * Preloaded source and destination csets. Used to guarantee
+ * atomic success or failure on actual migration.
+ */
+ struct list_head preloaded_src_csets;
+ struct list_head preloaded_dst_csets;
+
+ /* tasks and csets to migrate */
+ struct cgroup_taskset tset;
+};
+
+#define CGROUP_TASKSET_INIT(tset) \
+{ \
+ .src_csets = LIST_HEAD_INIT(tset.src_csets), \
+ .dst_csets = LIST_HEAD_INIT(tset.dst_csets), \
+ .csets = &tset.src_csets, \
+}
+
+#define CGROUP_MGCTX_INIT(name) \
+{ \
+ LIST_HEAD_INIT(name.preloaded_src_csets), \
+ LIST_HEAD_INIT(name.preloaded_dst_csets), \
+ CGROUP_TASKSET_INIT(name.tset), \
+}
+
+#define DEFINE_CGROUP_MGCTX(name) \
+ struct cgroup_mgctx name = CGROUP_MGCTX_INIT(name)
+
struct cgroup_sb_opts {
u16 subsys_mask;
unsigned int flags;
@@ -112,13 +167,12 @@ struct dentry *cgroup_do_mount(struct file_system_type *fs_type, int flags,
struct cgroup_namespace *ns);
bool cgroup_may_migrate_to(struct cgroup *dst_cgrp);
-void cgroup_migrate_finish(struct list_head *preloaded_csets);
-void cgroup_migrate_add_src(struct css_set *src_cset,
- struct cgroup *dst_cgrp,
- struct list_head *preloaded_csets);
-int cgroup_migrate_prepare_dst(struct list_head *preloaded_csets);
+void cgroup_migrate_finish(struct cgroup_mgctx *mgctx);
+void cgroup_migrate_add_src(struct css_set *src_cset, struct cgroup *dst_cgrp,
+ struct cgroup_mgctx *mgctx);
+int cgroup_migrate_prepare_dst(struct cgroup_mgctx *mgctx);
int cgroup_migrate(struct task_struct *leader, bool threadgroup,
- struct cgroup_root *root);
+ struct cgroup_mgctx *mgctx, struct cgroup_root *root);
int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader,
bool threadgroup);
diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index 465b101..7a965f4 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -87,7 +87,7 @@ EXPORT_SYMBOL_GPL(cgroup_attach_task_all);
*/
int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from)
{
- LIST_HEAD(preloaded_csets);
+ DEFINE_CGROUP_MGCTX(mgctx);
struct cgrp_cset_link *link;
struct css_task_iter it;
struct task_struct *task;
@@ -106,10 +106,10 @@ int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from)
/* all tasks in @from are being moved, all csets are source */
spin_lock_irq(&css_set_lock);
list_for_each_entry(link, &from->cset_links, cset_link)
- cgroup_migrate_add_src(link->cset, to, &preloaded_csets);
+ cgroup_migrate_add_src(link->cset, to, &mgctx);
spin_unlock_irq(&css_set_lock);
- ret = cgroup_migrate_prepare_dst(&preloaded_csets);
+ ret = cgroup_migrate_prepare_dst(&mgctx);
if (ret)
goto out_err;
@@ -125,14 +125,14 @@ int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from)
css_task_iter_end(&it);
if (task) {
- ret = cgroup_migrate(task, false, to->root);
+ ret = cgroup_migrate(task, false, &mgctx, to->root);
if (!ret)
trace_cgroup_transfer_tasks(to, task, false);
put_task_struct(task);
}
} while (task && !ret);
out_err:
- cgroup_migrate_finish(&preloaded_csets);
+ cgroup_migrate_finish(&mgctx);
percpu_up_write(&cgroup_threadgroup_rwsem);
mutex_unlock(&cgroup_mutex);
return ret;
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index aed492e..f90554d 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -1916,49 +1916,18 @@ int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
}
EXPORT_SYMBOL_GPL(task_cgroup_path);
-/* used to track tasks and other necessary states during migration */
-struct cgroup_taskset {
- /* the src and dst cset list running through cset->mg_node */
- struct list_head src_csets;
- struct list_head dst_csets;
-
- /* the subsys currently being processed */
- int ssid;
-
- /*
- * Fields for cgroup_taskset_*() iteration.
- *
- * Before migration is committed, the target migration tasks are on
- * ->mg_tasks of the csets on ->src_csets. After, on ->mg_tasks of
- * the csets on ->dst_csets. ->csets point to either ->src_csets
- * or ->dst_csets depending on whether migration is committed.
- *
- * ->cur_csets and ->cur_task point to the current task position
- * during iteration.
- */
- struct list_head *csets;
- struct css_set *cur_cset;
- struct task_struct *cur_task;
-};
-
-#define CGROUP_TASKSET_INIT(tset) (struct cgroup_taskset){ \
- .src_csets = LIST_HEAD_INIT(tset.src_csets), \
- .dst_csets = LIST_HEAD_INIT(tset.dst_csets), \
- .csets = &tset.src_csets, \
-}
-
/**
- * cgroup_taskset_add - try to add a migration target task to a taskset
+ * cgroup_migrate_add_task - add a migration target task to a migration context
* @task: target task
- * @tset: target taskset
+ * @mgctx: target migration context
*
- * Add @task, which is a migration target, to @tset. This function becomes
- * noop if @task doesn't need to be migrated. @task's css_set should have
- * been added as a migration source and @task->cg_list will be moved from
- * the css_set's tasks list to mg_tasks one.
+ * Add @task, which is a migration target, to @mgctx->tset. This function
+ * becomes noop if @task doesn't need to be migrated. @task's css_set
+ * should have been added as a migration source and @task->cg_list will be
+ * moved from the css_set's tasks list to mg_tasks one.
*/
-static void cgroup_taskset_add(struct task_struct *task,
- struct cgroup_taskset *tset)
+static void cgroup_migrate_add_task(struct task_struct *task,
+ struct cgroup_mgctx *mgctx)
{
struct css_set *cset;
@@ -1978,10 +1947,11 @@ static void cgroup_taskset_add(struct task_struct *task,
list_move_tail(&task->cg_list, &cset->mg_tasks);
if (list_empty(&cset->mg_node))
- list_add_tail(&cset->mg_node, &tset->src_csets);
+ list_add_tail(&cset->mg_node,
+ &mgctx->tset.src_csets);
if (list_empty(&cset->mg_dst_cset->mg_node))
list_add_tail(&cset->mg_dst_cset->mg_node,
- &tset->dst_csets);
+ &mgctx->tset.dst_csets);
}
/**
@@ -2048,17 +2018,18 @@ struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset,
/**
* cgroup_taskset_migrate - migrate a taskset
- * @tset: taget taskset
+ * @mgctx: migration context
* @root: cgroup root the migration is taking place on
*
- * Migrate tasks in @tset as setup by migration preparation functions.
+ * Migrate tasks in @mgctx as setup by migration preparation functions.
* This function fails iff one of the ->can_attach callbacks fails and
- * guarantees that either all or none of the tasks in @tset are migrated.
- * @tset is consumed regardless of success.
+ * guarantees that either all or none of the tasks in @mgctx are migrated.
+ * @mgctx is consumed regardless of success.
*/
-static int cgroup_taskset_migrate(struct cgroup_taskset *tset,
+static int cgroup_migrate_execute(struct cgroup_mgctx *mgctx,
struct cgroup_root *root)
{
+ struct cgroup_taskset *tset = &mgctx->tset;
struct cgroup_subsys *ss;
struct task_struct *task, *tmp_task;
struct css_set *cset, *tmp_cset;
@@ -2151,25 +2122,31 @@ bool cgroup_may_migrate_to(struct cgroup *dst_cgrp)
/**
* cgroup_migrate_finish - cleanup after attach
- * @preloaded_csets: list of preloaded css_sets
+ * @mgctx: migration context
*
* Undo cgroup_migrate_add_src() and cgroup_migrate_prepare_dst(). See
* those functions for details.
*/
-void cgroup_migrate_finish(struct list_head *preloaded_csets)
+void cgroup_migrate_finish(struct cgroup_mgctx *mgctx)
{
+ LIST_HEAD(preloaded);
struct css_set *cset, *tmp_cset;
lockdep_assert_held(&cgroup_mutex);
spin_lock_irq(&css_set_lock);
- list_for_each_entry_safe(cset, tmp_cset, preloaded_csets, mg_preload_node) {
+
+ list_splice_tail_init(&mgctx->preloaded_src_csets, &preloaded);
+ list_splice_tail_init(&mgctx->preloaded_dst_csets, &preloaded);
+
+ list_for_each_entry_safe(cset, tmp_cset, &preloaded, mg_preload_node) {
cset->mg_src_cgrp = NULL;
cset->mg_dst_cgrp = NULL;
cset->mg_dst_cset = NULL;
list_del_init(&cset->mg_preload_node);
put_css_set_locked(cset);
}
+
spin_unlock_irq(&css_set_lock);
}
@@ -2177,10 +2154,10 @@ void cgroup_migrate_finish(struct list_head *preloaded_csets)
* cgroup_migrate_add_src - add a migration source css_set
* @src_cset: the source css_set to add
* @dst_cgrp: the destination cgroup
- * @preloaded_csets: list of preloaded css_sets
+ * @mgctx: migration context
*
* Tasks belonging to @src_cset are about to be migrated to @dst_cgrp. Pin
- * @src_cset and add it to @preloaded_csets, which should later be cleaned
+ * @src_cset and add it to @mgctx->src_csets, which should later be cleaned
* up by cgroup_migrate_finish().
*
* This function may be called without holding cgroup_threadgroup_rwsem
@@ -2191,7 +2168,7 @@ void cgroup_migrate_finish(struct list_head *preloaded_csets)
*/
void cgroup_migrate_add_src(struct css_set *src_cset,
struct cgroup *dst_cgrp,
- struct list_head *preloaded_csets)
+ struct cgroup_mgctx *mgctx)
{
struct cgroup *src_cgrp;
@@ -2219,32 +2196,32 @@ void cgroup_migrate_add_src(struct css_set *src_cset,
src_cset->mg_src_cgrp = src_cgrp;
src_cset->mg_dst_cgrp = dst_cgrp;
get_css_set(src_cset);
- list_add(&src_cset->mg_preload_node, preloaded_csets);
+ list_add_tail(&src_cset->mg_preload_node, &mgctx->preloaded_src_csets);
}
/**
* cgroup_migrate_prepare_dst - prepare destination css_sets for migration
- * @preloaded_csets: list of preloaded source css_sets
+ * @mgctx: migration context
*
* 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.
+ * preloaded to @mgctx->preloaded_src_csets. This function looks up and
+ * pins all destination css_sets, links each to its source, and append them
+ * to @mgctx->preloaded_dst_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.
+ * @mgctx.
*/
-int cgroup_migrate_prepare_dst(struct list_head *preloaded_csets)
+int cgroup_migrate_prepare_dst(struct cgroup_mgctx *mgctx)
{
- LIST_HEAD(csets);
struct css_set *src_cset, *tmp_cset;
lockdep_assert_held(&cgroup_mutex);
/* 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) {
+ list_for_each_entry_safe(src_cset, tmp_cset, &mgctx->preloaded_src_csets,
+ mg_preload_node) {
struct css_set *dst_cset;
dst_cset = find_css_set(src_cset, src_cset->mg_dst_cgrp);
@@ -2270,15 +2247,15 @@ int cgroup_migrate_prepare_dst(struct list_head *preloaded_csets)
src_cset->mg_dst_cset = dst_cset;
if (list_empty(&dst_cset->mg_preload_node))
- list_add(&dst_cset->mg_preload_node, &csets);
+ list_add_tail(&dst_cset->mg_preload_node,
+ &mgctx->preloaded_dst_csets);
else
put_css_set(dst_cset);
}
- list_splice_tail(&csets, preloaded_csets);
return 0;
err:
- cgroup_migrate_finish(&csets);
+ cgroup_migrate_finish(mgctx);
return -ENOMEM;
}
@@ -2287,6 +2264,7 @@ int cgroup_migrate_prepare_dst(struct list_head *preloaded_csets)
* @leader: the leader of the process or the task to migrate
* @threadgroup: whether @leader points to the whole process or a single task
* @root: cgroup root migration is taking place on
+ * @mgctx: migration context
*
* Migrate a process or task denoted by @leader. If migrating a process,
* the caller must be holding cgroup_threadgroup_rwsem. The caller is also
@@ -2301,9 +2279,8 @@ int cgroup_migrate_prepare_dst(struct list_head *preloaded_csets)
* actually starting migrating.
*/
int cgroup_migrate(struct task_struct *leader, bool threadgroup,
- struct cgroup_root *root)
+ struct cgroup_mgctx *mgctx, struct cgroup_root *root)
{
- struct cgroup_taskset tset = CGROUP_TASKSET_INIT(tset);
struct task_struct *task;
/*
@@ -2315,14 +2292,14 @@ int cgroup_migrate(struct task_struct *leader, bool threadgroup,
rcu_read_lock();
task = leader;
do {
- cgroup_taskset_add(task, &tset);
+ cgroup_migrate_add_task(task, mgctx);
if (!threadgroup)
break;
} while_each_thread(leader, task);
rcu_read_unlock();
spin_unlock_irq(&css_set_lock);
- return cgroup_taskset_migrate(&tset, root);
+ return cgroup_migrate_execute(mgctx, root);
}
/**
@@ -2336,7 +2313,7 @@ int cgroup_migrate(struct task_struct *leader, bool threadgroup,
int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader,
bool threadgroup)
{
- LIST_HEAD(preloaded_csets);
+ DEFINE_CGROUP_MGCTX(mgctx);
struct task_struct *task;
int ret;
@@ -2348,8 +2325,7 @@ int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader,
rcu_read_lock();
task = leader;
do {
- cgroup_migrate_add_src(task_css_set(task), dst_cgrp,
- &preloaded_csets);
+ cgroup_migrate_add_src(task_css_set(task), dst_cgrp, &mgctx);
if (!threadgroup)
break;
} while_each_thread(leader, task);
@@ -2357,11 +2333,11 @@ int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader,
spin_unlock_irq(&css_set_lock);
/* prepare dst csets and commit */
- ret = cgroup_migrate_prepare_dst(&preloaded_csets);
+ ret = cgroup_migrate_prepare_dst(&mgctx);
if (!ret)
- ret = cgroup_migrate(leader, threadgroup, dst_cgrp->root);
+ ret = cgroup_migrate(leader, threadgroup, &mgctx, dst_cgrp->root);
- cgroup_migrate_finish(&preloaded_csets);
+ cgroup_migrate_finish(&mgctx);
if (!ret)
trace_cgroup_attach_task(dst_cgrp, leader, threadgroup);
@@ -2528,8 +2504,7 @@ static int cgroup_subtree_control_show(struct seq_file *seq, void *v)
*/
static int cgroup_update_dfl_csses(struct cgroup *cgrp)
{
- LIST_HEAD(preloaded_csets);
- struct cgroup_taskset tset = CGROUP_TASKSET_INIT(tset);
+ DEFINE_CGROUP_MGCTX(mgctx);
struct cgroup_subsys_state *d_css;
struct cgroup *dsct;
struct css_set *src_cset;
@@ -2545,33 +2520,28 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp)
struct cgrp_cset_link *link;
list_for_each_entry(link, &dsct->cset_links, cset_link)
- cgroup_migrate_add_src(link->cset, dsct,
- &preloaded_csets);
+ cgroup_migrate_add_src(link->cset, dsct, &mgctx);
}
spin_unlock_irq(&css_set_lock);
/* NULL dst indicates self on default hierarchy */
- ret = cgroup_migrate_prepare_dst(&preloaded_csets);
+ ret = cgroup_migrate_prepare_dst(&mgctx);
if (ret)
goto out_finish;
spin_lock_irq(&css_set_lock);
- list_for_each_entry(src_cset, &preloaded_csets, mg_preload_node) {
+ list_for_each_entry(src_cset, &mgctx.preloaded_src_csets, mg_preload_node) {
struct task_struct *task, *ntask;
- /* src_csets precede dst_csets, break on the first dst_cset */
- if (!src_cset->mg_src_cgrp)
- break;
-
/* all tasks in src_csets need to be migrated */
list_for_each_entry_safe(task, ntask, &src_cset->tasks, cg_list)
- cgroup_taskset_add(task, &tset);
+ cgroup_migrate_add_task(task, &mgctx);
}
spin_unlock_irq(&css_set_lock);
- ret = cgroup_taskset_migrate(&tset, cgrp->root);
+ ret = cgroup_migrate_execute(&mgctx, cgrp->root);
out_finish:
- cgroup_migrate_finish(&preloaded_csets);
+ cgroup_migrate_finish(&mgctx);
percpu_up_write(&cgroup_threadgroup_rwsem);
return ret;
}
--
2.9.3