}
/**
- * blkg_lookup_create - lookup blkg, try to create one if not there
+ * __blkg_lookup_create - lookup blkg, try to create one if not there
* @blkcg: blkcg of interest
* @q: request_queue of interest
*
* that all non-root blkg's have access to the parent blkg. This function
* should be called under RCU read lock and @q->queue_lock.
*
- * Returns pointer to the looked up or created blkg on success, ERR_PTR()
- * value on error. If @q is dead, returns ERR_PTR(-EINVAL). If @q is not
- * dead and bypassing, returns ERR_PTR(-EBUSY).
+ * Returns the blkg or the closest blkg if blkg_create fails as it walks
+ * down from root.
*/
-struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
- struct request_queue *q)
+struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
+ struct request_queue *q)
{
struct blkcg_gq *blkg;
* we shouldn't allow anything to go through for a bypassing queue.
*/
if (unlikely(blk_queue_bypass(q)))
- return ERR_PTR(blk_queue_dying(q) ? -ENODEV : -EBUSY);
+ return q->root_blkg;
blkg = __blkg_lookup(blkcg, q, true);
if (blkg)
/*
* Create blkgs walking down from blkcg_root to @blkcg, so that all
- * non-root blkgs have access to their parents.
+ * non-root blkgs have access to their parents. Returns the closest
+ * blkg to the intended blkg should blkg_create() fail.
*/
while (true) {
struct blkcg *pos = blkcg;
struct blkcg *parent = blkcg_parent(blkcg);
-
- while (parent && !__blkg_lookup(parent, q, false)) {
+ struct blkcg_gq *ret_blkg = q->root_blkg;
+
+ while (parent) {
+ blkg = __blkg_lookup(parent, q, false);
+ if (blkg) {
+ /* remember closest blkg */
+ ret_blkg = blkg;
+ break;
+ }
pos = parent;
parent = blkcg_parent(parent);
}
blkg = blkg_create(pos, q, NULL);
- if (pos == blkcg || IS_ERR(blkg))
+ if (IS_ERR(blkg))
+ return ret_blkg;
+ if (pos == blkcg)
return blkg;
}
}
-static void blkg_pd_offline(struct blkcg_gq *blkg)
+/**
+ * blkg_lookup_create - find or create a blkg
+ * @blkcg: target block cgroup
+ * @q: target request_queue
+ *
+ * This looks up or creates the blkg representing the unique pair
+ * of the blkcg and the request_queue.
+ */
+struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
+ struct request_queue *q)
{
- int i;
+ struct blkcg_gq *blkg = blkg_lookup(blkcg, q);
+ unsigned long flags;
- lockdep_assert_held(blkg->q->queue_lock);
- lockdep_assert_held(&blkg->blkcg->lock);
+ if (unlikely(!blkg)) {
+ spin_lock_irqsave(q->queue_lock, flags);
- for (i = 0; i < BLKCG_MAX_POLS; i++) {
- struct blkcg_policy *pol = blkcg_policy[i];
+ blkg = __blkg_lookup_create(blkcg, q);
- if (blkg->pd[i] && !blkg->pd[i]->offline &&
- pol->pd_offline_fn) {
- pol->pd_offline_fn(blkg->pd[i]);
- blkg->pd[i]->offline = true;
- }
+ spin_unlock_irqrestore(q->queue_lock, flags);
}
+
+ return blkg;
}
static void blkg_destroy(struct blkcg_gq *blkg)
{
struct blkcg *blkcg = blkg->blkcg;
struct blkcg_gq *parent = blkg->parent;
+ int i;
lockdep_assert_held(blkg->q->queue_lock);
lockdep_assert_held(&blkcg->lock);
WARN_ON_ONCE(list_empty(&blkg->q_node));
WARN_ON_ONCE(hlist_unhashed(&blkg->blkcg_node));
+ for (i = 0; i < BLKCG_MAX_POLS; i++) {
+ struct blkcg_policy *pol = blkcg_policy[i];
+
+ if (blkg->pd[i] && pol->pd_offline_fn)
+ pol->pd_offline_fn(blkg->pd[i]);
+ }
+
if (parent) {
blkg_rwstat_add_aux(&parent->stat_bytes, &blkg->stat_bytes);
blkg_rwstat_add_aux(&parent->stat_ios, &blkg->stat_ios);
struct blkcg *blkcg = blkg->blkcg;
spin_lock(&blkcg->lock);
- blkg_pd_offline(blkg);
blkg_destroy(blkg);
spin_unlock(&blkcg->lock);
}
{ } /* terminate */
};
+/*
+ * blkcg destruction is a three-stage process.
+ *
+ * 1. Destruction starts. The blkcg_css_offline() callback is invoked
+ * which offlines writeback. Here we tie the next stage of blkg destruction
+ * to the completion of writeback associated with the blkcg. This lets us
+ * avoid punting potentially large amounts of outstanding writeback to root
+ * while maintaining any ongoing policies. The next stage is triggered when
+ * the nr_cgwbs count goes to zero.
+ *
+ * 2. When the nr_cgwbs count goes to zero, blkcg_destroy_blkgs() is called
+ * and handles the destruction of blkgs. Here the css reference held by
+ * the blkg is put back eventually allowing blkcg_css_free() to be called.
+ * This work may occur in cgwb_release_workfn() on the cgwb_release
+ * workqueue. Any submitted ios that fail to get the blkg ref will be
+ * punted to the root_blkg.
+ *
+ * 3. Once the blkcg ref count goes to zero, blkcg_css_free() is called.
+ * This finally frees the blkcg.
+ */
+
/**
* blkcg_css_offline - cgroup css_offline callback
* @css: css of interest
*
- * This function is called when @css is about to go away and responsible
- * for offlining all blkgs pd and killing all wbs associated with @css.
- * blkgs pd offline should be done while holding both q and blkcg locks.
- * As blkcg lock is nested inside q lock, this function performs reverse
- * double lock dancing.
- *
- * This is the blkcg counterpart of ioc_release_fn().
+ * This function is called when @css is about to go away. Here the cgwbs are
+ * offlined first and only once writeback associated with the blkcg has
+ * finished do we start step 2 (see above).
*/
static void blkcg_css_offline(struct cgroup_subsys_state *css)
{
struct blkcg *blkcg = css_to_blkcg(css);
- struct blkcg_gq *blkg;
-
- spin_lock_irq(&blkcg->lock);
-
- hlist_for_each_entry(blkg, &blkcg->blkg_list, blkcg_node) {
- struct request_queue *q = blkg->q;
-
- if (spin_trylock(q->queue_lock)) {
- blkg_pd_offline(blkg);
- spin_unlock(q->queue_lock);
- } else {
- spin_unlock_irq(&blkcg->lock);
- cpu_relax();
- spin_lock_irq(&blkcg->lock);
- }
- }
-
- spin_unlock_irq(&blkcg->lock);
+ /* this prevents anyone from attaching or migrating to this blkcg */
wb_blkcg_offline(blkcg);
+
+ /* put the base cgwb reference allowing step 2 to be triggered */
+ blkcg_cgwb_put(blkcg);
}
/**
- * blkcg_destroy_all_blkgs - destroy all blkgs associated with a blkcg
+ * blkcg_destroy_blkgs - responsible for shooting down blkgs
* @blkcg: blkcg of interest
*
- * This function is called when blkcg css is about to free and responsible for
- * destroying all blkgs associated with @blkcg.
- * blkgs should be removed while holding both q and blkcg locks. As blkcg lock
+ * blkgs should be removed while holding both q and blkcg locks. As blkcg lock
* is nested inside q lock, this function performs reverse double lock dancing.
+ * Destroying the blkgs releases the reference held on the blkcg's css allowing
+ * blkcg_css_free to eventually be called.
+ *
+ * This is the blkcg counterpart of ioc_release_fn().
*/
-static void blkcg_destroy_all_blkgs(struct blkcg *blkcg)
+void blkcg_destroy_blkgs(struct blkcg *blkcg)
{
spin_lock_irq(&blkcg->lock);
+
while (!hlist_empty(&blkcg->blkg_list)) {
struct blkcg_gq *blkg = hlist_entry(blkcg->blkg_list.first,
- struct blkcg_gq,
- blkcg_node);
+ struct blkcg_gq, blkcg_node);
struct request_queue *q = blkg->q;
if (spin_trylock(q->queue_lock)) {
spin_lock_irq(&blkcg->lock);
}
}
+
spin_unlock_irq(&blkcg->lock);
}
struct blkcg *blkcg = css_to_blkcg(css);
int i;
- blkcg_destroy_all_blkgs(blkcg);
-
mutex_lock(&blkcg_pol_mutex);
list_del(&blkcg->all_blkcgs_node);
INIT_HLIST_HEAD(&blkcg->blkg_list);
#ifdef CONFIG_CGROUP_WRITEBACK
INIT_LIST_HEAD(&blkcg->cgwb_list);
+ refcount_set(&blkcg->cgwb_refcnt, 1);
#endif
list_add_tail(&blkcg->all_blkcgs_node, &all_blkcgs);
list_for_each_entry(blkg, &q->blkg_list, q_node) {
if (blkg->pd[pol->plid]) {
- if (!blkg->pd[pol->plid]->offline &&
- pol->pd_offline_fn) {
+ if (pol->pd_offline_fn)
pol->pd_offline_fn(blkg->pd[pol->plid]);
- blkg->pd[pol->plid]->offline = true;
- }
pol->pd_free_fn(blkg->pd[pol->plid]);
blkg->pd[pol->plid] = NULL;
}
projects / linux-2.6-microblaze.git / blobdiff