diff options
Diffstat (limited to 'block/blk-ioc.c')
-rw-r--r-- | block/blk-ioc.c | 485 |
1 files changed, 400 insertions, 85 deletions
diff --git a/block/blk-ioc.c b/block/blk-ioc.c index 6f9bbd978653..27a06e00eaec 100644 --- a/block/blk-ioc.c +++ b/block/blk-ioc.c @@ -16,53 +16,214 @@ */ static struct kmem_cache *iocontext_cachep; -static void cfq_dtor(struct io_context *ioc) +/** + * get_io_context - increment reference count to io_context + * @ioc: io_context to get + * + * Increment reference count to @ioc. + */ +void get_io_context(struct io_context *ioc) +{ + BUG_ON(atomic_long_read(&ioc->refcount) <= 0); + atomic_long_inc(&ioc->refcount); +} +EXPORT_SYMBOL(get_io_context); + +/* + * Releasing ioc may nest into another put_io_context() leading to nested + * fast path release. As the ioc's can't be the same, this is okay but + * makes lockdep whine. Keep track of nesting and use it as subclass. + */ +#ifdef CONFIG_LOCKDEP +#define ioc_release_depth(q) ((q) ? (q)->ioc_release_depth : 0) +#define ioc_release_depth_inc(q) (q)->ioc_release_depth++ +#define ioc_release_depth_dec(q) (q)->ioc_release_depth-- +#else +#define ioc_release_depth(q) 0 +#define ioc_release_depth_inc(q) do { } while (0) +#define ioc_release_depth_dec(q) do { } while (0) +#endif + +static void icq_free_icq_rcu(struct rcu_head *head) +{ + struct io_cq *icq = container_of(head, struct io_cq, __rcu_head); + + kmem_cache_free(icq->__rcu_icq_cache, icq); +} + +/* + * Exit and free an icq. Called with both ioc and q locked. + */ +static void ioc_exit_icq(struct io_cq *icq) { - if (!hlist_empty(&ioc->cic_list)) { - struct cfq_io_context *cic; + struct io_context *ioc = icq->ioc; + struct request_queue *q = icq->q; + struct elevator_type *et = q->elevator->type; + + lockdep_assert_held(&ioc->lock); + lockdep_assert_held(q->queue_lock); + + radix_tree_delete(&ioc->icq_tree, icq->q->id); + hlist_del_init(&icq->ioc_node); + list_del_init(&icq->q_node); + + /* + * Both setting lookup hint to and clearing it from @icq are done + * under queue_lock. If it's not pointing to @icq now, it never + * will. Hint assignment itself can race safely. + */ + if (rcu_dereference_raw(ioc->icq_hint) == icq) + rcu_assign_pointer(ioc->icq_hint, NULL); - cic = hlist_entry(ioc->cic_list.first, struct cfq_io_context, - cic_list); - cic->dtor(ioc); + if (et->ops.elevator_exit_icq_fn) { + ioc_release_depth_inc(q); + et->ops.elevator_exit_icq_fn(icq); + ioc_release_depth_dec(q); } + + /* + * @icq->q might have gone away by the time RCU callback runs + * making it impossible to determine icq_cache. Record it in @icq. + */ + icq->__rcu_icq_cache = et->icq_cache; + call_rcu(&icq->__rcu_head, icq_free_icq_rcu); } /* - * IO Context helper functions. put_io_context() returns 1 if there are no - * more users of this io context, 0 otherwise. + * Slow path for ioc release in put_io_context(). Performs double-lock + * dancing to unlink all icq's and then frees ioc. */ -int put_io_context(struct io_context *ioc) +static void ioc_release_fn(struct work_struct *work) { - if (ioc == NULL) - return 1; + struct io_context *ioc = container_of(work, struct io_context, + release_work); + struct request_queue *last_q = NULL; - BUG_ON(atomic_long_read(&ioc->refcount) == 0); + spin_lock_irq(&ioc->lock); - if (atomic_long_dec_and_test(&ioc->refcount)) { - rcu_read_lock(); - cfq_dtor(ioc); - rcu_read_unlock(); + while (!hlist_empty(&ioc->icq_list)) { + struct io_cq *icq = hlist_entry(ioc->icq_list.first, + struct io_cq, ioc_node); + struct request_queue *this_q = icq->q; - kmem_cache_free(iocontext_cachep, ioc); - return 1; + if (this_q != last_q) { + /* + * Need to switch to @this_q. Once we release + * @ioc->lock, it can go away along with @cic. + * Hold on to it. + */ + __blk_get_queue(this_q); + + /* + * blk_put_queue() might sleep thanks to kobject + * idiocy. Always release both locks, put and + * restart. + */ + if (last_q) { + spin_unlock(last_q->queue_lock); + spin_unlock_irq(&ioc->lock); + blk_put_queue(last_q); + } else { + spin_unlock_irq(&ioc->lock); + } + + last_q = this_q; + spin_lock_irq(this_q->queue_lock); + spin_lock(&ioc->lock); + continue; + } + ioc_exit_icq(icq); } - return 0; + + if (last_q) { + spin_unlock(last_q->queue_lock); + spin_unlock_irq(&ioc->lock); + blk_put_queue(last_q); + } else { + spin_unlock_irq(&ioc->lock); + } + + kmem_cache_free(iocontext_cachep, ioc); } -EXPORT_SYMBOL(put_io_context); -static void cfq_exit(struct io_context *ioc) +/** + * put_io_context - put a reference of io_context + * @ioc: io_context to put + * @locked_q: request_queue the caller is holding queue_lock of (hint) + * + * Decrement reference count of @ioc and release it if the count reaches + * zero. If the caller is holding queue_lock of a queue, it can indicate + * that with @locked_q. This is an optimization hint and the caller is + * allowed to pass in %NULL even when it's holding a queue_lock. + */ +void put_io_context(struct io_context *ioc, struct request_queue *locked_q) { - rcu_read_lock(); + struct request_queue *last_q = locked_q; + unsigned long flags; + + if (ioc == NULL) + return; + + BUG_ON(atomic_long_read(&ioc->refcount) <= 0); + if (locked_q) + lockdep_assert_held(locked_q->queue_lock); - if (!hlist_empty(&ioc->cic_list)) { - struct cfq_io_context *cic; + if (!atomic_long_dec_and_test(&ioc->refcount)) + return; + + /* + * Destroy @ioc. This is a bit messy because icq's are chained + * from both ioc and queue, and ioc->lock nests inside queue_lock. + * The inner ioc->lock should be held to walk our icq_list and then + * for each icq the outer matching queue_lock should be grabbed. + * ie. We need to do reverse-order double lock dancing. + * + * Another twist is that we are often called with one of the + * matching queue_locks held as indicated by @locked_q, which + * prevents performing double-lock dance for other queues. + * + * So, we do it in two stages. The fast path uses the queue_lock + * the caller is holding and, if other queues need to be accessed, + * uses trylock to avoid introducing locking dependency. This can + * handle most cases, especially if @ioc was performing IO on only + * single device. + * + * If trylock doesn't cut it, we defer to @ioc->release_work which + * can do all the double-locking dancing. + */ + spin_lock_irqsave_nested(&ioc->lock, flags, + ioc_release_depth(locked_q)); - cic = hlist_entry(ioc->cic_list.first, struct cfq_io_context, - cic_list); - cic->exit(ioc); + while (!hlist_empty(&ioc->icq_list)) { + struct io_cq *icq = hlist_entry(ioc->icq_list.first, + struct io_cq, ioc_node); + struct request_queue *this_q = icq->q; + + if (this_q != last_q) { + if (last_q && last_q != locked_q) + spin_unlock(last_q->queue_lock); + last_q = NULL; + + if (!spin_trylock(this_q->queue_lock)) + break; + last_q = this_q; + continue; + } + ioc_exit_icq(icq); } - rcu_read_unlock(); + + if (last_q && last_q != locked_q) + spin_unlock(last_q->queue_lock); + + spin_unlock_irqrestore(&ioc->lock, flags); + + /* if no icq is left, we're done; otherwise, kick release_work */ + if (hlist_empty(&ioc->icq_list)) + kmem_cache_free(iocontext_cachep, ioc); + else + schedule_work(&ioc->release_work); } +EXPORT_SYMBOL(put_io_context); /* Called by the exiting task */ void exit_io_context(struct task_struct *task) @@ -74,86 +235,240 @@ void exit_io_context(struct task_struct *task) task->io_context = NULL; task_unlock(task); - if (atomic_dec_and_test(&ioc->nr_tasks)) - cfq_exit(ioc); + atomic_dec(&ioc->nr_tasks); + put_io_context(ioc, NULL); +} + +/** + * ioc_clear_queue - break any ioc association with the specified queue + * @q: request_queue being cleared + * + * Walk @q->icq_list and exit all io_cq's. Must be called with @q locked. + */ +void ioc_clear_queue(struct request_queue *q) +{ + lockdep_assert_held(q->queue_lock); + + while (!list_empty(&q->icq_list)) { + struct io_cq *icq = list_entry(q->icq_list.next, + struct io_cq, q_node); + struct io_context *ioc = icq->ioc; - put_io_context(ioc); + spin_lock(&ioc->lock); + ioc_exit_icq(icq); + spin_unlock(&ioc->lock); + } } -struct io_context *alloc_io_context(gfp_t gfp_flags, int node) +void create_io_context_slowpath(struct task_struct *task, gfp_t gfp_flags, + int node) { struct io_context *ioc; - ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags, node); - if (ioc) { - atomic_long_set(&ioc->refcount, 1); - atomic_set(&ioc->nr_tasks, 1); - spin_lock_init(&ioc->lock); - ioc->ioprio_changed = 0; - ioc->ioprio = 0; - ioc->last_waited = 0; /* doesn't matter... */ - ioc->nr_batch_requests = 0; /* because this is 0 */ - INIT_RADIX_TREE(&ioc->radix_root, GFP_ATOMIC | __GFP_HIGH); - INIT_HLIST_HEAD(&ioc->cic_list); - ioc->ioc_data = NULL; -#if defined(CONFIG_BLK_CGROUP) || defined(CONFIG_BLK_CGROUP_MODULE) - ioc->cgroup_changed = 0; -#endif - } + ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO, + node); + if (unlikely(!ioc)) + return; - return ioc; + /* initialize */ + atomic_long_set(&ioc->refcount, 1); + atomic_set(&ioc->nr_tasks, 1); + spin_lock_init(&ioc->lock); + INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC | __GFP_HIGH); + INIT_HLIST_HEAD(&ioc->icq_list); + INIT_WORK(&ioc->release_work, ioc_release_fn); + + /* + * Try to install. ioc shouldn't be installed if someone else + * already did or @task, which isn't %current, is exiting. Note + * that we need to allow ioc creation on exiting %current as exit + * path may issue IOs from e.g. exit_files(). The exit path is + * responsible for not issuing IO after exit_io_context(). + */ + task_lock(task); + if (!task->io_context && + (task == current || !(task->flags & PF_EXITING))) + task->io_context = ioc; + else + kmem_cache_free(iocontext_cachep, ioc); + task_unlock(task); } -/* - * If the current task has no IO context then create one and initialise it. - * Otherwise, return its existing IO context. +/** + * get_task_io_context - get io_context of a task + * @task: task of interest + * @gfp_flags: allocation flags, used if allocation is necessary + * @node: allocation node, used if allocation is necessary * - * This returned IO context doesn't have a specifically elevated refcount, - * but since the current task itself holds a reference, the context can be - * used in general code, so long as it stays within `current` context. + * Return io_context of @task. If it doesn't exist, it is created with + * @gfp_flags and @node. The returned io_context has its reference count + * incremented. + * + * This function always goes through task_lock() and it's better to use + * %current->io_context + get_io_context() for %current. */ -struct io_context *current_io_context(gfp_t gfp_flags, int node) +struct io_context *get_task_io_context(struct task_struct *task, + gfp_t gfp_flags, int node) { - struct task_struct *tsk = current; - struct io_context *ret; - - ret = tsk->io_context; - if (likely(ret)) - return ret; - - ret = alloc_io_context(gfp_flags, node); - if (ret) { - /* make sure set_task_ioprio() sees the settings above */ - smp_wmb(); - tsk->io_context = ret; - } + struct io_context *ioc; - return ret; + might_sleep_if(gfp_flags & __GFP_WAIT); + + do { + task_lock(task); + ioc = task->io_context; + if (likely(ioc)) { + get_io_context(ioc); + task_unlock(task); + return ioc; + } + task_unlock(task); + } while (create_io_context(task, gfp_flags, node)); + + return NULL; } +EXPORT_SYMBOL(get_task_io_context); -/* - * If the current task has no IO context then create one and initialise it. - * If it does have a context, take a ref on it. +/** + * ioc_lookup_icq - lookup io_cq from ioc + * @ioc: the associated io_context + * @q: the associated request_queue * - * This is always called in the context of the task which submitted the I/O. + * Look up io_cq associated with @ioc - @q pair from @ioc. Must be called + * with @q->queue_lock held. */ -struct io_context *get_io_context(gfp_t gfp_flags, int node) +struct io_cq *ioc_lookup_icq(struct io_context *ioc, struct request_queue *q) { - struct io_context *ioc = NULL; + struct io_cq *icq; + + lockdep_assert_held(q->queue_lock); /* - * Check for unlikely race with exiting task. ioc ref count is - * zero when ioc is being detached. + * icq's are indexed from @ioc using radix tree and hint pointer, + * both of which are protected with RCU. All removals are done + * holding both q and ioc locks, and we're holding q lock - if we + * find a icq which points to us, it's guaranteed to be valid. */ - do { - ioc = current_io_context(gfp_flags, node); - if (unlikely(!ioc)) - break; - } while (!atomic_long_inc_not_zero(&ioc->refcount)); + rcu_read_lock(); + icq = rcu_dereference(ioc->icq_hint); + if (icq && icq->q == q) + goto out; - return ioc; + icq = radix_tree_lookup(&ioc->icq_tree, q->id); + if (icq && icq->q == q) + rcu_assign_pointer(ioc->icq_hint, icq); /* allowed to race */ + else + icq = NULL; +out: + rcu_read_unlock(); + return icq; } -EXPORT_SYMBOL(get_io_context); +EXPORT_SYMBOL(ioc_lookup_icq); + +/** + * ioc_create_icq - create and link io_cq + * @q: request_queue of interest + * @gfp_mask: allocation mask + * + * Make sure io_cq linking %current->io_context and @q exists. If either + * io_context and/or icq don't exist, they will be created using @gfp_mask. + * + * The caller is responsible for ensuring @ioc won't go away and @q is + * alive and will stay alive until this function returns. + */ +struct io_cq *ioc_create_icq(struct request_queue *q, gfp_t gfp_mask) +{ + struct elevator_type *et = q->elevator->type; + struct io_context *ioc; + struct io_cq *icq; + + /* allocate stuff */ + ioc = create_io_context(current, gfp_mask, q->node); + if (!ioc) + return NULL; + + icq = kmem_cache_alloc_node(et->icq_cache, gfp_mask | __GFP_ZERO, + q->node); + if (!icq) + return NULL; + + if (radix_tree_preload(gfp_mask) < 0) { + kmem_cache_free(et->icq_cache, icq); + return NULL; + } + + icq->ioc = ioc; + icq->q = q; + INIT_LIST_HEAD(&icq->q_node); + INIT_HLIST_NODE(&icq->ioc_node); + + /* lock both q and ioc and try to link @icq */ + spin_lock_irq(q->queue_lock); + spin_lock(&ioc->lock); + + if (likely(!radix_tree_insert(&ioc->icq_tree, q->id, icq))) { + hlist_add_head(&icq->ioc_node, &ioc->icq_list); + list_add(&icq->q_node, &q->icq_list); + if (et->ops.elevator_init_icq_fn) + et->ops.elevator_init_icq_fn(icq); + } else { + kmem_cache_free(et->icq_cache, icq); + icq = ioc_lookup_icq(ioc, q); + if (!icq) + printk(KERN_ERR "cfq: icq link failed!\n"); + } + + spin_unlock(&ioc->lock); + spin_unlock_irq(q->queue_lock); + radix_tree_preload_end(); + return icq; +} + +void ioc_set_changed(struct io_context *ioc, int which) +{ + struct io_cq *icq; + struct hlist_node *n; + + hlist_for_each_entry(icq, n, &ioc->icq_list, ioc_node) + set_bit(which, &icq->changed); +} + +/** + * ioc_ioprio_changed - notify ioprio change + * @ioc: io_context of interest + * @ioprio: new ioprio + * + * @ioc's ioprio has changed to @ioprio. Set %ICQ_IOPRIO_CHANGED for all + * icq's. iosched is responsible for checking the bit and applying it on + * request issue path. + */ +void ioc_ioprio_changed(struct io_context *ioc, int ioprio) +{ + unsigned long flags; + + spin_lock_irqsave(&ioc->lock, flags); + ioc->ioprio = ioprio; + ioc_set_changed(ioc, ICQ_IOPRIO_CHANGED); + spin_unlock_irqrestore(&ioc->lock, flags); +} + +/** + * ioc_cgroup_changed - notify cgroup change + * @ioc: io_context of interest + * + * @ioc's cgroup has changed. Set %ICQ_CGROUP_CHANGED for all icq's. + * iosched is responsible for checking the bit and applying it on request + * issue path. + */ +void ioc_cgroup_changed(struct io_context *ioc) +{ + unsigned long flags; + + spin_lock_irqsave(&ioc->lock, flags); + ioc_set_changed(ioc, ICQ_CGROUP_CHANGED); + spin_unlock_irqrestore(&ioc->lock, flags); +} +EXPORT_SYMBOL(ioc_cgroup_changed); static int __init blk_ioc_init(void) { |