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Commit 7ee9c562 authored by Tejun Heo's avatar Tejun Heo Committed by Jens Axboe
Browse files

blkcg: let blkio_group point to blkio_cgroup directly 



Currently, blkg points to the associated blkcg via its css_id.  This
unnecessarily complicates dereferencing blkcg.  Let blkg hold a
reference to the associated blkcg and point directly to it and disable
css_id on blkio_subsys.

This change requires splitting blkiocg_destroy() into
blkiocg_pre_destroy() and blkiocg_destroy() so that all blkg's can be
destroyed and all the blkcg references held by them dropped during
cgroup removal.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 92616b5b

block/blk-cgroup.c

+24 −19
Original line number Diff line number Diff line
@@ -37,6 +37,7 @@ static int blkiocg_can_attach(struct cgroup_subsys *, struct cgroup *, 
			      struct cgroup_taskset *);

static void blkiocg_attach(struct cgroup_subsys *, struct cgroup *,

			   struct cgroup_taskset *);

static int blkiocg_pre_destroy(struct cgroup_subsys *, struct cgroup *);

static void blkiocg_destroy(struct cgroup_subsys *, struct cgroup *);

static int blkiocg_populate(struct cgroup_subsys *, struct cgroup *);
@@ -51,10 +52,10 @@ struct cgroup_subsys blkio_subsys = { 
	.create = blkiocg_create,

	.can_attach = blkiocg_can_attach,

	.attach = blkiocg_attach,

	.pre_destroy = blkiocg_pre_destroy,

	.destroy = blkiocg_destroy,

	.populate = blkiocg_populate,

	.subsys_id = blkio_subsys_id,

	.use_id = 1,

	.module = THIS_MODULE,

};

EXPORT_SYMBOL_GPL(blkio_subsys);
@@ -442,6 +443,7 @@ struct blkio_group *blkg_lookup_create(struct blkio_cgroup *blkcg, 
	if (blkg)

		return blkg;



	/* blkg holds a reference to blkcg */

	if (!css_tryget(&blkcg->css))

		return ERR_PTR(-EINVAL);
@@ -463,15 +465,16 @@ struct blkio_group *blkg_lookup_create(struct blkio_cgroup *blkcg, 


		spin_lock_init(&new_blkg->stats_lock);

		rcu_assign_pointer(new_blkg->q, q);

		new_blkg->blkcg_id = css_id(&blkcg->css);

		new_blkg->blkcg = blkcg;

		new_blkg->plid = plid;

		cgroup_path(blkcg->css.cgroup, new_blkg->path,

			    sizeof(new_blkg->path));

	} else {

		css_put(&blkcg->css);

	}



	rcu_read_lock();

	spin_lock_irq(q->queue_lock);

	css_put(&blkcg->css);



	/* did bypass get turned on inbetween? */

	if (unlikely(blk_queue_bypass(q)) && !for_root) {
@@ -500,6 +503,7 @@ out: 
	if (new_blkg) {

		free_percpu(new_blkg->stats_cpu);

		kfree(new_blkg);

		css_put(&blkcg->css);

	}

	return blkg;

}
@@ -508,7 +512,6 @@ EXPORT_SYMBOL_GPL(blkg_lookup_create); 
static void __blkiocg_del_blkio_group(struct blkio_group *blkg)

{

	hlist_del_init_rcu(&blkg->blkcg_node);

	blkg->blkcg_id = 0;

}



/*
@@ -517,24 +520,17 @@ static void __blkiocg_del_blkio_group(struct blkio_group *blkg) 
 */

int blkiocg_del_blkio_group(struct blkio_group *blkg)

{

	struct blkio_cgroup *blkcg;

	struct blkio_cgroup *blkcg = blkg->blkcg;

	unsigned long flags;

	struct cgroup_subsys_state *css;

	int ret = 1;



	rcu_read_lock();

	css = css_lookup(&blkio_subsys, blkg->blkcg_id);

	if (css) {

		blkcg = container_of(css, struct blkio_cgroup, css);

	spin_lock_irqsave(&blkcg->lock, flags);

	if (!hlist_unhashed(&blkg->blkcg_node)) {

		__blkiocg_del_blkio_group(blkg);

		ret = 0;

	}

	spin_unlock_irqrestore(&blkcg->lock, flags);

	}



	rcu_read_unlock();

	return ret;

}

EXPORT_SYMBOL_GPL(blkiocg_del_blkio_group);
@@ -1387,7 +1383,8 @@ static int blkiocg_populate(struct cgroup_subsys *subsys, struct cgroup *cgroup) 
				ARRAY_SIZE(blkio_files));

}



static void blkiocg_destroy(struct cgroup_subsys *subsys, struct cgroup *cgroup)

static int blkiocg_pre_destroy(struct cgroup_subsys *subsys,

			       struct cgroup *cgroup)

{

	struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgroup);

	unsigned long flags;
@@ -1396,6 +1393,7 @@ static void blkiocg_destroy(struct cgroup_subsys *subsys, struct cgroup *cgroup) 
	struct blkio_policy_type *blkiop;



	rcu_read_lock();



	do {

		spin_lock_irqsave(&blkcg->lock, flags);
@@ -1425,8 +1423,15 @@ static void blkiocg_destroy(struct cgroup_subsys *subsys, struct cgroup *cgroup) 
		spin_unlock(&blkio_list_lock);

	} while (1);



	free_css_id(&blkio_subsys, &blkcg->css);

	rcu_read_unlock();



	return 0;

}



static void blkiocg_destroy(struct cgroup_subsys *subsys, struct cgroup *cgroup)

{

	struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgroup);



	if (blkcg != &blkio_root_cgroup)

		kfree(blkcg);

}

block/blk-cgroup.h

+1 −1
Original line number Diff line number Diff line
@@ -163,7 +163,7 @@ struct blkio_group { 
	/* Pointer to the associated request_queue, RCU protected */

	struct request_queue __rcu *q;

	struct hlist_node blkcg_node;

	unsigned short blkcg_id;

	struct blkio_cgroup *blkcg;

	/* Store cgroup path */

	char path[128];

	/* policy which owns this blk group */

block/blk-throttle.c

+3 −0
Original line number Diff line number Diff line
@@ -169,6 +169,9 @@ static void throtl_put_tg(struct throtl_grp *tg) 
	if (!atomic_dec_and_test(&tg->ref))

		return;



	/* release the extra blkcg reference this blkg has been holding */

	css_put(&tg->blkg.blkcg->css);



	/*

	 * A group is freed in rcu manner. But having an rcu lock does not

	 * mean that one can access all the fields of blkg and assume these

block/cfq-iosched.c

+4 −0
Original line number Diff line number Diff line
@@ -1133,6 +1133,10 @@ static void cfq_put_cfqg(struct cfq_group *cfqg) 
	cfqg->ref--;

	if (cfqg->ref)

		return;



	/* release the extra blkcg reference this blkg has been holding */

	css_put(&cfqg->blkg.blkcg->css);



	for_each_cfqg_st(cfqg, i, j, st)

		BUG_ON(!RB_EMPTY_ROOT(&st->rb));

	free_percpu(cfqg->blkg.stats_cpu);