diff options
| -rw-r--r-- | block/blk-cgroup.c | 75 |
1 files changed, 52 insertions, 23 deletions
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index 7ef747b7f056..201275467d8b 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) |