3 files changed, 146 insertions, 66 deletions

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index dc00835..2788693 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1649,7 +1649,7 @@ static void blkiocg_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
 	ioc = get_task_io_context(tsk, GFP_ATOMIC, NUMA_NO_NODE);
 	if (ioc) {
 		ioc_cgroup_changed(ioc);
-		put_io_context(ioc);
+		put_io_context(ioc, NULL);
 	}
 }
 
diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index 6f59fba..fb23965 100644
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -29,55 +29,164 @@ void get_io_context(struct io_context *ioc)
 }
 EXPORT_SYMBOL(get_io_context);
 
-static void cfq_dtor(struct io_context *ioc)
+/*
+ * 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
+
+/*
+ * Slow path for ioc release in put_io_context().  Performs double-lock
+ * dancing to unlink all cic's and then frees ioc.
+ */
+static void ioc_release_fn(struct work_struct *work)
 {
-	if (!hlist_empty(&ioc->cic_list)) {
-		struct cfq_io_context *cic;
+	struct io_context *ioc = container_of(work, struct io_context,
+					      release_work);
+	struct request_queue *last_q = NULL;
+
+	spin_lock_irq(&ioc->lock);
+
+	while (!hlist_empty(&ioc->cic_list)) {
+		struct cfq_io_context *cic = hlist_entry(ioc->cic_list.first,
+							 struct cfq_io_context,
+							 cic_list);
+		struct request_queue *this_q = cic->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;
+		}
+		ioc_release_depth_inc(this_q);
+		cic->exit(cic);
+		cic->release(cic);
+		ioc_release_depth_dec(this_q);
+	}
 
-		cic = hlist_entry(ioc->cic_list.first, struct cfq_io_context,
-								cic_list);
-		cic->dtor(ioc);
+	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);
 }
 
 /**
  * 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.
+ * 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)
+void put_io_context(struct io_context *ioc, struct request_queue *locked_q)
 {
+	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;
 
-	rcu_read_lock();
-	cfq_dtor(ioc);
-	rcu_read_unlock();
-
-	kmem_cache_free(iocontext_cachep, ioc);
-}
-EXPORT_SYMBOL(put_io_context);
+	/*
+	 * Destroy @ioc.  This is a bit messy because cic'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 cic_list and then
+	 * for each cic 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));
+
+	while (!hlist_empty(&ioc->cic_list)) {
+		struct cfq_io_context *cic = hlist_entry(ioc->cic_list.first,
+							 struct cfq_io_context,
+							 cic_list);
+		struct request_queue *this_q = cic->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_release_depth_inc(this_q);
+		cic->exit(cic);
+		cic->release(cic);
+		ioc_release_depth_dec(this_q);
+	}
 
-static void cfq_exit(struct io_context *ioc)
-{
-	rcu_read_lock();
+	if (last_q && last_q != locked_q)
+		spin_unlock(last_q->queue_lock);
 
-	if (!hlist_empty(&ioc->cic_list)) {
-		struct cfq_io_context *cic;
+	spin_unlock_irqrestore(&ioc->lock, flags);
 
-		cic = hlist_entry(ioc->cic_list.first, struct cfq_io_context,
-								cic_list);
-		cic->exit(ioc);
-	}
-	rcu_read_unlock();
+	/* if no cic's left, we're done; otherwise, kick release_work */
+	if (hlist_empty(&ioc->cic_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)
@@ -92,10 +201,8 @@ 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);
-
-	put_io_context(ioc);
+	atomic_dec(&ioc->nr_tasks);
+	put_io_context(ioc, NULL);
 }
 
 static struct io_context *create_task_io_context(struct task_struct *task,
@@ -115,6 +222,7 @@ static struct io_context *create_task_io_context(struct task_struct *task,
 	spin_lock_init(&ioc->lock);
 	INIT_RADIX_TREE(&ioc->radix_root, GFP_ATOMIC | __GFP_HIGH);
 	INIT_HLIST_HEAD(&ioc->cic_list);
+	INIT_WORK(&ioc->release_work, ioc_release_fn);
 
 	/* try to install, somebody might already have beaten us to it */
 	task_lock(task);
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index e617b08..6cc6065 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1778,7 +1778,7 @@ __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->ioc);
+		put_io_context(cfqd->active_cic->ioc, cfqd->queue);
 		cfqd->active_cic = NULL;
 	}
 }
@@ -2812,38 +2812,6 @@ static void cfq_exit_cic(struct cfq_io_context *cic)
 	}
 }
 
-static void cfq_exit_single_io_context(struct io_context *ioc,
-				       struct cfq_io_context *cic)
-{
-	struct cfq_data *cfqd = cic_to_cfqd(cic);
-
-	if (cfqd) {
-		struct request_queue *q = cfqd->queue;
-		unsigned long flags;
-
-		spin_lock_irqsave(q->queue_lock, flags);
-
-		/*
-		 * Ensure we get a fresh copy of the ->key to prevent
-		 * race between exiting task and queue
-		 */
-		smp_read_barrier_depends();
-		if (cic->key == cfqd)
-			cfq_exit_cic(cic);
-
-		spin_unlock_irqrestore(q->queue_lock, flags);
-	}
-}
-
-/*
- * The process that ioc belongs to has exited, we need to clean up
- * and put the internal structures we have that belongs to that process.
- */
-static void cfq_exit_io_context(struct io_context *ioc)
-{
-	call_for_each_cic(ioc, cfq_exit_single_io_context);
-}
-
 static struct cfq_io_context *
 cfq_alloc_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
 {
@@ -2855,8 +2823,8 @@ cfq_alloc_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
 		cic->ttime.last_end_request = jiffies;
 		INIT_LIST_HEAD(&cic->queue_list);
 		INIT_HLIST_NODE(&cic->cic_list);
-		cic->dtor = cfq_free_io_context;
-		cic->exit = cfq_exit_io_context;
+		cic->exit = cfq_exit_cic;
+		cic->release = cfq_release_cic;
 		elv_ioc_count_inc(cfq_ioc_count);
 	}
 
@@ -3726,7 +3694,7 @@ static void cfq_put_request(struct request *rq)
 		BUG_ON(!cfqq->allocated[rw]);
 		cfqq->allocated[rw]--;
 
-		put_io_context(RQ_CIC(rq)->ioc);
+		put_io_context(RQ_CIC(rq)->ioc, cfqq->cfqd->queue);
 
 		rq->elevator_private[0] = NULL;
 		rq->elevator_private[1] = NULL;
@@ -3937,8 +3905,12 @@ static void cfq_exit_queue(struct elevator_queue *e)
 		struct cfq_io_context *cic = list_entry(cfqd->cic_list.next,
 							struct cfq_io_context,
 							queue_list);
+		struct io_context *ioc = cic->ioc;
 
+		spin_lock(&ioc->lock);
 		cfq_exit_cic(cic);
+		cfq_release_cic(cic);
+		spin_unlock(&ioc->lock);
 	}
 
 	cfq_put_async_queues(cfqd);