}
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.
- */
+/* 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;
if (rcu_dereference_raw(ioc->icq_hint) == icq)
rcu_assign_pointer(ioc->icq_hint, NULL);
- if (et->ops.elevator_exit_icq_fn) {
- ioc_release_depth_inc(q);
- et->ops.elevator_exit_icq_fn(icq);
- ioc_release_depth_dec(q);
- }
+ ioc_exit_icq(icq);
/*
* @icq->q might have gone away by the time RCU callback runs
{
struct io_context *ioc = container_of(work, struct io_context,
release_work);
- struct request_queue *last_q = NULL;
+ unsigned long flags;
- spin_lock_irq(&ioc->lock);
+ /*
+ * 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 *this_q = icq->q;
-
- 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;
+ 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_relax();
+ spin_lock_irqsave_nested(&ioc->lock, flags, 1);
}
- ioc_exit_icq(icq);
}
- 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);
- }
+ 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
- * @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.
+ * zero.
*/
-void put_io_context(struct io_context *ioc, struct request_queue *locked_q)
+void put_io_context(struct io_context *ioc)
{
- struct request_queue *last_q = locked_q;
unsigned long flags;
+ bool free_ioc = false;
if (ioc == NULL)
return;
BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
- if (locked_q)
- lockdep_assert_held(locked_q->queue_lock);
-
- 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.
+ * Releasing ioc requires reverse order double locking and we may
+ * already be holding a queue_lock. Do it asynchronously from wq.
*/
- spin_lock_irqsave_nested(&ioc->lock, flags,
- ioc_release_depth(locked_q));
-
- 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);
+ if (atomic_long_dec_and_test(&ioc->refcount)) {
+ spin_lock_irqsave(&ioc->lock, flags);
+ if (!hlist_empty(&ioc->icq_list))
+ schedule_work(&ioc->release_work);
+ else
+ free_ioc = true;
+ spin_unlock_irqrestore(&ioc->lock, flags);
}
- 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))
+ if (free_ioc)
kmem_cache_free(iocontext_cachep, ioc);
- else
- schedule_work(&ioc->release_work);
}
EXPORT_SYMBOL(put_io_context);
void exit_io_context(struct task_struct *task)
{
struct io_context *ioc;
+ struct io_cq *icq;
+ struct hlist_node *n;
+ unsigned long flags;
task_lock(task);
ioc = task->io_context;
task->io_context = NULL;
task_unlock(task);
- atomic_dec(&ioc->nr_tasks);
- put_io_context(ioc, NULL);
+ if (!atomic_dec_and_test(&ioc->nr_tasks)) {
+ 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, n, &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_relax();
+ goto retry;
+ }
+ }
+ spin_unlock_irqrestore(&ioc->lock, flags);
+
+ put_io_context(ioc);
}
/**
struct io_context *ioc = icq->ioc;
spin_lock(&ioc->lock);
- ioc_exit_icq(icq);
+ ioc_destroy_icq(icq);
spin_unlock(&ioc->lock);
}
}
return icq;
}
-void ioc_set_changed(struct io_context *ioc, int which)
+void ioc_set_icq_flags(struct io_context *ioc, unsigned int flags)
{
struct io_cq *icq;
struct hlist_node *n;
hlist_for_each_entry(icq, n, &ioc->icq_list, ioc_node)
- set_bit(which, &icq->changed);
+ icq->flags |= flags;
}
/**
spin_lock_irqsave(&ioc->lock, flags);
ioc->ioprio = ioprio;
- ioc_set_changed(ioc, ICQ_IOPRIO_CHANGED);
+ ioc_set_icq_flags(ioc, ICQ_IOPRIO_CHANGED);
spin_unlock_irqrestore(&ioc->lock, flags);
}
unsigned long flags;
spin_lock_irqsave(&ioc->lock, flags);
- ioc_set_changed(ioc, ICQ_CGROUP_CHANGED);
+ ioc_set_icq_flags(ioc, ICQ_CGROUP_CHANGED);
spin_unlock_irqrestore(&ioc->lock, flags);
}
EXPORT_SYMBOL(ioc_cgroup_changed);
+/**
+ * icq_get_changed - fetch and clear icq changed mask
+ * @icq: icq of interest
+ *
+ * Fetch and clear ICQ_*_CHANGED bits from @icq. Grabs and releases
+ * @icq->ioc->lock.
+ */
+unsigned icq_get_changed(struct io_cq *icq)
+{
+ unsigned int changed = 0;
+ unsigned long flags;
+
+ if (unlikely(icq->flags & ICQ_CHANGED_MASK)) {
+ spin_lock_irqsave(&icq->ioc->lock, flags);
+ changed = icq->flags & ICQ_CHANGED_MASK;
+ icq->flags &= ~ICQ_CHANGED_MASK;
+ spin_unlock_irqrestore(&icq->ioc->lock, flags);
+ }
+ return changed;
+}
+EXPORT_SYMBOL(icq_get_changed);
+
static int __init blk_ioc_init(void)
{
iocontext_cachep = kmem_cache_create("blkdev_ioc",
projects / karo-tx-linux.git / blobdiff