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Commit e595cd70 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: track migration context in cgroup_mgctx 



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: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarZefan Li <lizefan@huawei.com>
parent d8ebf519

kernel/cgroup/cgroup-internal.h

+60 −6
Original line number Diff line number Diff line
@@ -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);

kernel/cgroup/cgroup-v1.c

+5 −5
Original line number Diff line number Diff line
@@ -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;

kernel/cgroup/cgroup.c

+57 −87
Original line number Diff line number Diff line
@@ -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;

}