diff options
| -rw-r--r-- | block/blk-cgroup.c | 50 | ||||
| -rw-r--r-- | block/blk-core.c | 15 |
2 files changed, 46 insertions, 19 deletions
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index f6581a090b9d..d6e4555c982f 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -137,6 +137,38 @@ static struct blkio_group *blkg_alloc(struct blkio_cgroup *blkcg, return blkg; } +static struct blkio_group *__blkg_lookup(struct blkio_cgroup *blkcg, + struct request_queue *q) +{ + struct blkio_group *blkg; + struct hlist_node *n; + + hlist_for_each_entry_rcu(blkg, n, &blkcg->blkg_list, blkcg_node) + if (blkg->q == q) + return blkg; + return NULL; +} + +/** + * blkg_lookup - lookup blkg for the specified blkcg - q pair + * @blkcg: blkcg of interest + * @q: request_queue of interest + * + * Lookup blkg for the @blkcg - @q pair. This function should be called + * under RCU read lock and is guaranteed to return %NULL if @q is bypassing + * - see blk_queue_bypass_start() for details. + */ +struct blkio_group *blkg_lookup(struct blkio_cgroup *blkcg, + struct request_queue *q) +{ + WARN_ON_ONCE(!rcu_read_lock_held()); + + if (unlikely(blk_queue_bypass(q))) + return NULL; + return __blkg_lookup(blkcg, q); +} +EXPORT_SYMBOL_GPL(blkg_lookup); + struct blkio_group *blkg_lookup_create(struct blkio_cgroup *blkcg, struct request_queue *q, bool for_root) @@ -150,13 +182,11 @@ struct blkio_group *blkg_lookup_create(struct blkio_cgroup *blkcg, /* * This could be the first entry point of blkcg implementation and * we shouldn't allow anything to go through for a bypassing queue. - * The following can be removed if blkg lookup is guaranteed to - * fail on a bypassing queue. */ if (unlikely(blk_queue_bypass(q)) && !for_root) return ERR_PTR(blk_queue_dead(q) ? -EINVAL : -EBUSY); - blkg = blkg_lookup(blkcg, q); + blkg = __blkg_lookup(blkcg, q); if (blkg) return blkg; @@ -185,20 +215,6 @@ out: } EXPORT_SYMBOL_GPL(blkg_lookup_create); -/* called under rcu_read_lock(). */ -struct blkio_group *blkg_lookup(struct blkio_cgroup *blkcg, - struct request_queue *q) -{ - struct blkio_group *blkg; - struct hlist_node *n; - - hlist_for_each_entry_rcu(blkg, n, &blkcg->blkg_list, blkcg_node) - if (blkg->q == q) - return blkg; - return NULL; -} -EXPORT_SYMBOL_GPL(blkg_lookup); - static void blkg_destroy(struct blkio_group *blkg) { struct request_queue *q = blkg->q; diff --git a/block/blk-core.c b/block/blk-core.c index 991c1d6ef245..f2db628aa509 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -416,7 +416,8 @@ void blk_drain_queue(struct request_queue *q, bool drain_all) * In bypass mode, only the dispatch FIFO queue of @q is used. This * function makes @q enter bypass mode and drains all requests which were * throttled or issued before. On return, it's guaranteed that no request - * is being throttled or has ELVPRIV set. + * is being throttled or has ELVPRIV set and blk_queue_bypass() %true + * inside queue or RCU read lock. */ void blk_queue_bypass_start(struct request_queue *q) { @@ -426,6 +427,8 @@ void blk_queue_bypass_start(struct request_queue *q) spin_unlock_irq(q->queue_lock); blk_drain_queue(q, false); + /* ensure blk_queue_bypass() is %true inside RCU read lock */ + synchronize_rcu(); } EXPORT_SYMBOL_GPL(blk_queue_bypass_start); @@ -462,7 +465,15 @@ void blk_cleanup_queue(struct request_queue *q) spin_lock_irq(lock); - /* dead queue is permanently in bypass mode till released */ + /* + * Dead queue is permanently in bypass mode till released. Note + * that, unlike blk_queue_bypass_start(), we aren't performing + * synchronize_rcu() after entering bypass mode to avoid the delay + * as some drivers create and destroy a lot of queues while + * probing. This is still safe because blk_release_queue() will be + * called only after the queue refcnt drops to zero and nothing, + * RCU or not, would be traversing the queue by then. + */ q->bypass_depth++; queue_flag_set(QUEUE_FLAG_BYPASS, q); |
