--- /dev/null
+/*
+ * Functions related to io context handling
+ */
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/bio.h>
+#include <linux/blkdev.h>
+#include <linux/slab.h>
+#include <linux/delay.h>
+
+#include "blk.h"
+
+/*
+ * For io context allocations
+ */
+static struct kmem_cache *iocontext_cachep;
+
+/**
+ * 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);
+
+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 an icq. Called with both ioc and q locked. */
+static void ioc_exit_icq(struct io_cq *icq)
+{
+ struct elevator_type *et = icq->q->elevator->type;
+
+ if (icq->flags & ICQ_EXITED)
+ return;
+
+ if (et->ops.elevator_exit_icq_fn)
+ et->ops.elevator_exit_icq_fn(icq);
+
+ icq->flags |= ICQ_EXITED;
+}
+
+/* Release an icq. Called with both ioc and q locked. */
+static void ioc_destroy_icq(struct io_cq *icq)
+{
+ 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_access_pointer(ioc->icq_hint) == icq)
+ rcu_assign_pointer(ioc->icq_hint, NULL);
+
+ ioc_exit_icq(icq);
+
+ /*
+ * @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);
+}
+
+/*
+ * Slow path for ioc release in put_io_context(). Performs double-lock
+ * dancing to unlink all icq's and then frees ioc.
+ */
+static void ioc_release_fn(struct work_struct *work)
+{
+ struct io_context *ioc = container_of(work, struct io_context,
+ release_work);
+ unsigned long flags;
+
+ /*
+ * Exiting icq may call into put_io_context() through elevator
+ * which will trigger lockdep warning. The ioc's are guaranteed to
+ * be different, use a different locking subclass here. Use
+ * irqsave variant as there's no spin_lock_irq_nested().
+ */
+ spin_lock_irqsave_nested(&ioc->lock, flags, 1);
+
+ while (!hlist_empty(&ioc->icq_list)) {
+ struct io_cq *icq = hlist_entry(ioc->icq_list.first,
+ struct io_cq, ioc_node);
+ struct request_queue *q = icq->q;
+
+ if (spin_trylock(q->queue_lock)) {
+ ioc_destroy_icq(icq);
+ spin_unlock(q->queue_lock);
+ } else {
+ spin_unlock_irqrestore(&ioc->lock, flags);
+ cpu_chill();
+ spin_lock_irqsave_nested(&ioc->lock, flags, 1);
+ }
+ }
+
+ spin_unlock_irqrestore(&ioc->lock, flags);
+
+ kmem_cache_free(iocontext_cachep, ioc);
+}
+
+/**
+ * put_io_context - put a reference of io_context
+ * @ioc: io_context to put
+ *
+ * Decrement reference count of @ioc and release it if the count reaches
+ * zero.
+ */
+void put_io_context(struct io_context *ioc)
+{
+ unsigned long flags;
+ bool free_ioc = false;
+
+ if (ioc == NULL)
+ return;
+
+ BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
+
+ /*
+ * Releasing ioc requires reverse order double locking and we may
+ * already be holding a queue_lock. Do it asynchronously from wq.
+ */
+ if (atomic_long_dec_and_test(&ioc->refcount)) {
+ spin_lock_irqsave(&ioc->lock, flags);
+ if (!hlist_empty(&ioc->icq_list))
+ queue_work(system_power_efficient_wq,
+ &ioc->release_work);
+ else
+ free_ioc = true;
+ spin_unlock_irqrestore(&ioc->lock, flags);
+ }
+
+ if (free_ioc)
+ kmem_cache_free(iocontext_cachep, ioc);
+}
+EXPORT_SYMBOL(put_io_context);
+
+/**
+ * put_io_context_active - put active reference on ioc
+ * @ioc: ioc of interest
+ *
+ * Undo get_io_context_active(). If active reference reaches zero after
+ * put, @ioc can never issue further IOs and ioscheds are notified.
+ */
+void put_io_context_active(struct io_context *ioc)
+{
+ unsigned long flags;
+ struct io_cq *icq;
+
+ if (!atomic_dec_and_test(&ioc->active_ref)) {
+ put_io_context(ioc);
+ return;
+ }
+
+ /*
+ * Need ioc lock to walk icq_list and q lock to exit icq. Perform
+ * reverse double locking. Read comment in ioc_release_fn() for
+ * explanation on the nested locking annotation.
+ */
+retry:
+ spin_lock_irqsave_nested(&ioc->lock, flags, 1);
+ hlist_for_each_entry(icq, &ioc->icq_list, ioc_node) {
+ if (icq->flags & ICQ_EXITED)
+ continue;
+ if (spin_trylock(icq->q->queue_lock)) {
+ ioc_exit_icq(icq);
+ spin_unlock(icq->q->queue_lock);
+ } else {
+ spin_unlock_irqrestore(&ioc->lock, flags);
+ cpu_chill();
+ goto retry;
+ }
+ }
+ spin_unlock_irqrestore(&ioc->lock, flags);
+
+ put_io_context(ioc);
+}
+
+/* Called by the exiting task */
+void exit_io_context(struct task_struct *task)
+{
+ struct io_context *ioc;
+
+ task_lock(task);
+ ioc = task->io_context;
+ task->io_context = NULL;
+ task_unlock(task);
+
+ atomic_dec(&ioc->nr_tasks);
+ put_io_context_active(ioc);
+}
+
+/**
+ * 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;
+
+ spin_lock(&ioc->lock);
+ ioc_destroy_icq(icq);
+ spin_unlock(&ioc->lock);
+ }
+}
+
+int create_task_io_context(struct task_struct *task, gfp_t gfp_flags, int node)
+{
+ struct io_context *ioc;
+ int ret;
+
+ ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO,
+ node);
+ if (unlikely(!ioc))
+ return -ENOMEM;
+
+ /* initialize */
+ atomic_long_set(&ioc->refcount, 1);
+ atomic_set(&ioc->nr_tasks, 1);
+ atomic_set(&ioc->active_ref, 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);
+
+ ret = task->io_context ? 0 : -EBUSY;
+
+ task_unlock(task);
+
+ return ret;
+}
+
+/**
+ * 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
+ *
+ * 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 *get_task_io_context(struct task_struct *task,
+ gfp_t gfp_flags, int node)
+{
+ struct io_context *ioc;
+
+ 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_task_io_context(task, gfp_flags, node));
+
+ return NULL;
+}
+EXPORT_SYMBOL(get_task_io_context);
+
+/**
+ * ioc_lookup_icq - lookup io_cq from ioc
+ * @ioc: the associated io_context
+ * @q: the associated request_queue
+ *
+ * Look up io_cq associated with @ioc - @q pair from @ioc. Must be called
+ * with @q->queue_lock held.
+ */
+struct io_cq *ioc_lookup_icq(struct io_context *ioc, struct request_queue *q)
+{
+ struct io_cq *icq;
+
+ lockdep_assert_held(q->queue_lock);
+
+ /*
+ * 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.
+ */
+ rcu_read_lock();
+ icq = rcu_dereference(ioc->icq_hint);
+ if (icq && icq->q == q)
+ goto out;
+
+ 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(ioc_lookup_icq);
+
+/**
+ * ioc_create_icq - create and link io_cq
+ * @ioc: io_context of interest
+ * @q: request_queue of interest
+ * @gfp_mask: allocation mask
+ *
+ * Make sure io_cq linking @ioc and @q exists. If icq doesn'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 io_context *ioc, struct request_queue *q,
+ gfp_t gfp_mask)
+{
+ struct elevator_type *et = q->elevator->type;
+ struct io_cq *icq;
+
+ /* allocate stuff */
+ icq = kmem_cache_alloc_node(et->icq_cache, gfp_mask | __GFP_ZERO,
+ q->node);
+ if (!icq)
+ return NULL;
+
+ if (radix_tree_maybe_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;
+}
+
+static int __init blk_ioc_init(void)
+{
+ iocontext_cachep = kmem_cache_create("blkdev_ioc",
+ sizeof(struct io_context), 0, SLAB_PANIC, NULL);
+ return 0;
+}
+subsys_initcall(blk_ioc_init);
Code Review / kvmfornfv.git / blobdiff