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-rw-r--r--block/blk-cgroup.c75
1 files changed, 52 insertions, 23 deletions
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 7ef747b..2012754 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -126,7 +126,7 @@ err_free:
}
static struct blkcg_gq *__blkg_lookup(struct blkcg *blkcg,
- struct request_queue *q)
+ struct request_queue *q, bool update_hint)
{
struct blkcg_gq *blkg;
@@ -135,14 +135,19 @@ static struct blkcg_gq *__blkg_lookup(struct blkcg *blkcg,
return blkg;
/*
- * Hint didn't match. Look up from the radix tree. Note that we
- * may not be holding queue_lock and thus are not sure whether
- * @blkg from blkg_tree has already been removed or not, so we
- * can't update hint to the lookup result. Leave it to the caller.
+ * Hint didn't match. Look up from the radix tree. Note that the
+ * hint can only be updated under queue_lock as otherwise @blkg
+ * could have already been removed from blkg_tree. The caller is
+ * responsible for grabbing queue_lock if @update_hint.
*/
blkg = radix_tree_lookup(&blkcg->blkg_tree, q->id);
- if (blkg && blkg->q == q)
+ if (blkg && blkg->q == q) {
+ if (update_hint) {
+ lockdep_assert_held(q->queue_lock);
+ rcu_assign_pointer(blkcg->blkg_hint, blkg);
+ }
return blkg;
+ }
return NULL;
}
@@ -162,7 +167,7 @@ struct blkcg_gq *blkg_lookup(struct blkcg *blkcg, struct request_queue *q)
if (unlikely(blk_queue_bypass(q)))
return NULL;
- return __blkg_lookup(blkcg, q);
+ return __blkg_lookup(blkcg, q, false);
}
EXPORT_SYMBOL_GPL(blkg_lookup);
@@ -170,9 +175,9 @@ EXPORT_SYMBOL_GPL(blkg_lookup);
* If @new_blkg is %NULL, this function tries to allocate a new one as
* necessary using %GFP_ATOMIC. @new_blkg is always consumed on return.
*/
-static struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
- struct request_queue *q,
- struct blkcg_gq *new_blkg)
+static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
+ struct request_queue *q,
+ struct blkcg_gq *new_blkg)
{
struct blkcg_gq *blkg;
int ret;
@@ -180,13 +185,6 @@ static struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
WARN_ON_ONCE(!rcu_read_lock_held());
lockdep_assert_held(q->queue_lock);
- /* lookup and update hint on success, see __blkg_lookup() for details */
- blkg = __blkg_lookup(blkcg, q);
- if (blkg) {
- rcu_assign_pointer(blkcg->blkg_hint, blkg);
- goto out_free;
- }
-
/* blkg holds a reference to blkcg */
if (!css_tryget(&blkcg->css)) {
blkg = ERR_PTR(-EINVAL);
@@ -223,16 +221,39 @@ out_free:
return blkg;
}
+/**
+ * blkg_lookup_create - lookup blkg, try to create one if not there
+ * @blkcg: blkcg of interest
+ * @q: request_queue of interest
+ *
+ * Lookup blkg for the @blkcg - @q pair. If it doesn't exist, try to
+ * create one. 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).
+ */
struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
struct request_queue *q)
{
+ struct blkcg_gq *blkg;
+
+ WARN_ON_ONCE(!rcu_read_lock_held());
+ lockdep_assert_held(q->queue_lock);
+
/*
* This could be the first entry point of blkcg implementation and
* 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) ? -EINVAL : -EBUSY);
- return __blkg_lookup_create(blkcg, q, NULL);
+
+ blkg = __blkg_lookup(blkcg, q, true);
+ if (blkg)
+ return blkg;
+
+ return blkg_create(blkcg, q, NULL);
}
EXPORT_SYMBOL_GPL(blkg_lookup_create);
@@ -777,7 +798,7 @@ int blkcg_activate_policy(struct request_queue *q,
const struct blkcg_policy *pol)
{
LIST_HEAD(pds);
- struct blkcg_gq *blkg;
+ struct blkcg_gq *blkg, *new_blkg;
struct blkg_policy_data *pd, *n;
int cnt = 0, ret;
bool preloaded;
@@ -786,19 +807,27 @@ int blkcg_activate_policy(struct request_queue *q,
return 0;
/* preallocations for root blkg */
- blkg = blkg_alloc(&blkcg_root, q, GFP_KERNEL);
- if (!blkg)
+ new_blkg = blkg_alloc(&blkcg_root, q, GFP_KERNEL);
+ if (!new_blkg)
return -ENOMEM;
preloaded = !radix_tree_preload(GFP_KERNEL);
blk_queue_bypass_start(q);
- /* make sure the root blkg exists and count the existing blkgs */
+ /*
+ * Make sure the root blkg exists and count the existing blkgs. As
+ * @q is bypassing at this point, blkg_lookup_create() can't be
+ * used. Open code it.
+ */
spin_lock_irq(q->queue_lock);
rcu_read_lock();
- blkg = __blkg_lookup_create(&blkcg_root, q, blkg);
+ blkg = __blkg_lookup(&blkcg_root, q, false);
+ if (blkg)
+ blkg_free(new_blkg);
+ else
+ blkg = blkg_create(&blkcg_root, q, new_blkg);
rcu_read_unlock();
if (preloaded)
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