4 files changed, 14 insertions, 84 deletions

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index fa8f26309444..75642a352a8f 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1659,7 +1659,7 @@ static void blkiocg_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
                 ioc = get_task_io_context(task, GFP_ATOMIC, NUMA_NO_NODE);
                 if (ioc) {
                         ioc_cgroup_changed(ioc);
-                        put_io_context(ioc, NULL);
+                        put_io_context(ioc);
                 }
         }
 }
diff --git a/block/blk-core.c b/block/blk-core.c
index 636702575118..532b3a21b383 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -642,7 +642,7 @@ static inline void blk_free_request(struct request_queue *q, struct request *rq)
         if (rq->cmd_flags & REQ_ELVPRIV) {
                 elv_put_request(q, rq);
                 if (rq->elv.icq)
-                        put_io_context(rq->elv.icq->ioc, q);
+                        put_io_context(rq->elv.icq->ioc);
         }
 
         mempool_free(rq, q->rq.rq_pool);
diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index 7490b6da2453..9884fd7427fe 100644
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -29,21 +29,6 @@ void get_io_context(struct io_context *ioc)
 }
 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);
@@ -75,11 +60,8 @@ static void ioc_exit_icq(struct io_cq *icq)
         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);
+        if (et->ops.elevator_exit_icq_fn)
                 et->ops.elevator_exit_icq_fn(icq);
-                ioc_release_depth_dec(q);
-        }
 
         /*
          * @icq->q might have gone away by the time RCU callback runs
@@ -149,81 +131,29 @@ static void ioc_release_fn(struct work_struct *work)
 /**
  * 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;
 
         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;
-
-                        /* spin_trylock() always successes in UP case */
-                        if (this_q != locked_q &&
-                            !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);
+                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))
-                kmem_cache_free(iocontext_cachep, ioc);
-        else
-                schedule_work(&ioc->release_work);
 }
 EXPORT_SYMBOL(put_io_context);
 
@@ -238,7 +168,7 @@ void exit_io_context(struct task_struct *task)
         task_unlock(task);
 
         atomic_dec(&ioc->nr_tasks);
-        put_io_context(ioc, NULL);
+        put_io_context(ioc);
 }
 
 /**
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index da21c24dbed3..5684df6848bc 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1794,7 +1794,7 @@ __cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                 cfqd->active_queue = NULL;
 
         if (cfqd->active_cic) {
-                put_io_context(cfqd->active_cic->icq.ioc, cfqd->queue);
+                put_io_context(cfqd->active_cic->icq.ioc);
                 cfqd->active_cic = NULL;
         }
 }