diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index e17da94..0ac817b 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -822,7 +822,6 @@
 static struct cgroup_subsys_state *
 blkcg_css_alloc(struct cgroup_subsys_state *parent_css)
 {
-	static atomic64_t id_seq = ATOMIC64_INIT(0);
 	struct blkcg *blkcg;
 
 	if (!parent_css) {
@@ -836,7 +835,6 @@
 
 	blkcg->cfq_weight = CFQ_WEIGHT_DEFAULT;
 	blkcg->cfq_leaf_weight = CFQ_WEIGHT_DEFAULT;
-	blkcg->id = atomic64_inc_return(&id_seq); /* root is 0, start from 1 */
 done:
 	spin_lock_init(&blkcg->lock);
 	INIT_RADIX_TREE(&blkcg->blkg_tree, GFP_ATOMIC);
diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index d3fd7aa..c567865 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -50,9 +50,6 @@
 	struct blkcg_gq			*blkg_hint;
 	struct hlist_head		blkg_list;
 
-	/* for policies to test whether associated blkcg has changed */
-	uint64_t			id;
-
 	/* TODO: per-policy storage in blkcg */
 	unsigned int			cfq_weight;	/* belongs to cfq */
 	unsigned int			cfq_leaf_weight;
diff --git a/block/blk-core.c b/block/blk-core.c
index bf930f4..6946a42 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -83,18 +83,14 @@
  * @bdev:	device
  *
  * Locates the passed device's request queue and returns the address of its
- * backing_dev_info
- *
- * Will return NULL if the request queue cannot be located.
+ * backing_dev_info.  This function can only be called if @bdev is opened
+ * and the return value is never NULL.
  */
 struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev)
 {
-	struct backing_dev_info *ret = NULL;
 	struct request_queue *q = bdev_get_queue(bdev);
 
-	if (q)
-		ret = &q->backing_dev_info;
-	return ret;
+	return &q->backing_dev_info;
 }
 EXPORT_SYMBOL(blk_get_backing_dev_info);
 
@@ -933,9 +929,9 @@
  * Get a free request from @q.  This function may fail under memory
  * pressure or if @q is dead.
  *
- * Must be callled with @q->queue_lock held and,
- * Returns %NULL on failure, with @q->queue_lock held.
- * Returns !%NULL on success, with @q->queue_lock *not held*.
+ * Must be called with @q->queue_lock held and,
+ * Returns ERR_PTR on failure, with @q->queue_lock held.
+ * Returns request pointer on success, with @q->queue_lock *not held*.
  */
 static struct request *__get_request(struct request_list *rl, int rw_flags,
 				     struct bio *bio, gfp_t gfp_mask)
@@ -949,7 +945,7 @@
 	int may_queue;
 
 	if (unlikely(blk_queue_dying(q)))
-		return NULL;
+		return ERR_PTR(-ENODEV);
 
 	may_queue = elv_may_queue(q, rw_flags);
 	if (may_queue == ELV_MQUEUE_NO)
@@ -974,7 +970,7 @@
 					 * process is not a "batcher", and not
 					 * exempted by the IO scheduler
 					 */
-					return NULL;
+					return ERR_PTR(-ENOMEM);
 				}
 			}
 		}
@@ -992,7 +988,7 @@
 	 * allocated with any setting of ->nr_requests
 	 */
 	if (rl->count[is_sync] >= (3 * q->nr_requests / 2))
-		return NULL;
+		return ERR_PTR(-ENOMEM);
 
 	q->nr_rqs[is_sync]++;
 	rl->count[is_sync]++;
@@ -1097,7 +1093,7 @@
 rq_starved:
 	if (unlikely(rl->count[is_sync] == 0))
 		rl->starved[is_sync] = 1;
-	return NULL;
+	return ERR_PTR(-ENOMEM);
 }
 
 /**
@@ -1110,9 +1106,9 @@
  * Get a free request from @q.  If %__GFP_WAIT is set in @gfp_mask, this
  * function keeps retrying under memory pressure and fails iff @q is dead.
  *
- * Must be callled with @q->queue_lock held and,
- * Returns %NULL on failure, with @q->queue_lock held.
- * Returns !%NULL on success, with @q->queue_lock *not held*.
+ * Must be called with @q->queue_lock held and,
+ * Returns ERR_PTR on failure, with @q->queue_lock held.
+ * Returns request pointer on success, with @q->queue_lock *not held*.
  */
 static struct request *get_request(struct request_queue *q, int rw_flags,
 				   struct bio *bio, gfp_t gfp_mask)
@@ -1125,12 +1121,12 @@
 	rl = blk_get_rl(q, bio);	/* transferred to @rq on success */
 retry:
 	rq = __get_request(rl, rw_flags, bio, gfp_mask);
-	if (rq)
+	if (!IS_ERR(rq))
 		return rq;
 
 	if (!(gfp_mask & __GFP_WAIT) || unlikely(blk_queue_dying(q))) {
 		blk_put_rl(rl);
-		return NULL;
+		return rq;
 	}
 
 	/* wait on @rl and retry */
@@ -1167,7 +1163,7 @@
 
 	spin_lock_irq(q->queue_lock);
 	rq = get_request(q, rw, NULL, gfp_mask);
-	if (!rq)
+	if (IS_ERR(rq))
 		spin_unlock_irq(q->queue_lock);
 	/* q->queue_lock is unlocked at this point */
 
@@ -1219,8 +1215,8 @@
 {
 	struct request *rq = blk_get_request(q, bio_data_dir(bio), gfp_mask);
 
-	if (unlikely(!rq))
-		return ERR_PTR(-ENOMEM);
+	if (IS_ERR(rq))
+		return rq;
 
 	blk_rq_set_block_pc(rq);
 
@@ -1614,8 +1610,8 @@
 	 * Returns with the queue unlocked.
 	 */
 	req = get_request(q, rw_flags, bio, GFP_NOIO);
-	if (unlikely(!req)) {
-		bio_endio(bio, -ENODEV);	/* @q is dead */
+	if (IS_ERR(req)) {
+		bio_endio(bio, PTR_ERR(req));	/* @q is dead */
 		goto out_unlock;
 	}
 
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 383ea0c..067e600 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -224,9 +224,11 @@
 	struct blk_mq_hw_ctx *hctx;
 	struct request *rq;
 	struct blk_mq_alloc_data alloc_data;
+	int ret;
 
-	if (blk_mq_queue_enter(q))
-		return NULL;
+	ret = blk_mq_queue_enter(q);
+	if (ret)
+		return ERR_PTR(ret);
 
 	ctx = blk_mq_get_ctx(q);
 	hctx = q->mq_ops->map_queue(q, ctx->cpu);
@@ -246,6 +248,8 @@
 		ctx = alloc_data.ctx;
 	}
 	blk_mq_put_ctx(ctx);
+	if (!rq)
+		return ERR_PTR(-EWOULDBLOCK);
 	return rq;
 }
 EXPORT_SYMBOL(blk_mq_alloc_request);
diff --git a/block/bsg.c b/block/bsg.c
index ff46add..276e869 100644
--- a/block/bsg.c
+++ b/block/bsg.c
@@ -270,8 +270,8 @@
 	 * map scatter-gather elements separately and string them to request
 	 */
 	rq = blk_get_request(q, rw, GFP_KERNEL);
-	if (!rq)
-		return ERR_PTR(-ENOMEM);
+	if (IS_ERR(rq))
+		return rq;
 	blk_rq_set_block_pc(rq);
 
 	ret = blk_fill_sgv4_hdr_rq(q, rq, hdr, bd, has_write_perm);
@@ -285,8 +285,9 @@
 		}
 
 		next_rq = blk_get_request(q, READ, GFP_KERNEL);
-		if (!next_rq) {
-			ret = -ENOMEM;
+		if (IS_ERR(next_rq)) {
+			ret = PTR_ERR(next_rq);
+			next_rq = NULL;
 			goto out;
 		}
 		rq->next_rq = next_rq;
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 3f31cf9..6f2751d 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -299,7 +299,7 @@
 	struct cfq_ttime	ttime;
 	int			ioprio;		/* the current ioprio */
 #ifdef CONFIG_CFQ_GROUP_IOSCHED
-	uint64_t		blkcg_id;	/* the current blkcg ID */
+	uint64_t		blkcg_serial_nr; /* the current blkcg serial */
 #endif
 };
 
@@ -3547,17 +3547,17 @@
 {
 	struct cfq_data *cfqd = cic_to_cfqd(cic);
 	struct cfq_queue *sync_cfqq;
-	uint64_t id;
+	uint64_t serial_nr;
 
 	rcu_read_lock();
-	id = bio_blkcg(bio)->id;
+	serial_nr = bio_blkcg(bio)->css.serial_nr;
 	rcu_read_unlock();
 
 	/*
 	 * Check whether blkcg has changed.  The condition may trigger
 	 * spuriously on a newly created cic but there's no harm.
 	 */
-	if (unlikely(!cfqd) || likely(cic->blkcg_id == id))
+	if (unlikely(!cfqd) || likely(cic->blkcg_serial_nr == serial_nr))
 		return;
 
 	sync_cfqq = cic_to_cfqq(cic, 1);
@@ -3571,7 +3571,7 @@
 		cfq_put_queue(sync_cfqq);
 	}
 
-	cic->blkcg_id = id;
+	cic->blkcg_serial_nr = serial_nr;
 }
 #else
 static inline void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio) { }
diff --git a/block/compat_ioctl.c b/block/compat_ioctl.c
index 18b282c..f678c73 100644
--- a/block/compat_ioctl.c
+++ b/block/compat_ioctl.c
@@ -709,8 +709,6 @@
 		if (!arg)
 			return -EINVAL;
 		bdi = blk_get_backing_dev_info(bdev);
-		if (bdi == NULL)
-			return -ENOTTY;
 		return compat_put_long(arg,
 				       (bdi->ra_pages * PAGE_CACHE_SIZE) / 512);
 	case BLKROGET: /* compatible */
@@ -731,8 +729,6 @@
 		if (!capable(CAP_SYS_ADMIN))
 			return -EACCES;
 		bdi = blk_get_backing_dev_info(bdev);
-		if (bdi == NULL)
-			return -ENOTTY;
 		bdi->ra_pages = (arg * 512) / PAGE_CACHE_SIZE;
 		return 0;
 	case BLKGETSIZE:
diff --git a/block/ioctl.c b/block/ioctl.c
index d6cda81..6c7bf90 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -356,8 +356,6 @@
 		if (!arg)
 			return -EINVAL;
 		bdi = blk_get_backing_dev_info(bdev);
-		if (bdi == NULL)
-			return -ENOTTY;
 		return put_long(arg, (bdi->ra_pages * PAGE_CACHE_SIZE) / 512);
 	case BLKROGET:
 		return put_int(arg, bdev_read_only(bdev) != 0);
@@ -386,8 +384,6 @@
 		if(!capable(CAP_SYS_ADMIN))
 			return -EACCES;
 		bdi = blk_get_backing_dev_info(bdev);
-		if (bdi == NULL)
-			return -ENOTTY;
 		bdi->ra_pages = (arg * 512) / PAGE_CACHE_SIZE;
 		return 0;
 	case BLKBSZSET:
diff --git a/block/scsi_ioctl.c b/block/scsi_ioctl.c
index 9b8eaec..abb2e65 100644
--- a/block/scsi_ioctl.c
+++ b/block/scsi_ioctl.c
@@ -316,8 +316,8 @@
 
 	ret = -ENOMEM;
 	rq = blk_get_request(q, writing ? WRITE : READ, GFP_KERNEL);
-	if (!rq)
-		goto out;
+	if (IS_ERR(rq))
+		return PTR_ERR(rq);
 	blk_rq_set_block_pc(rq);
 
 	if (hdr->cmd_len > BLK_MAX_CDB) {
@@ -387,7 +387,6 @@
 		kfree(rq->cmd);
 out_put_request:
 	blk_put_request(rq);
-out:
 	return ret;
 }
 
@@ -457,8 +456,8 @@
 	}
 
 	rq = blk_get_request(q, in_len ? WRITE : READ, __GFP_WAIT);
-	if (!rq) {
-		err = -ENOMEM;
+	if (IS_ERR(rq)) {
+		err = PTR_ERR(rq);
 		goto error;
 	}
 	blk_rq_set_block_pc(rq);
@@ -548,6 +547,8 @@
 	int err;
 
 	rq = blk_get_request(q, WRITE, __GFP_WAIT);
+	if (IS_ERR(rq))
+		return PTR_ERR(rq);
 	blk_rq_set_block_pc(rq);
 	rq->timeout = BLK_DEFAULT_SG_TIMEOUT;
 	rq->cmd[0] = cmd;
diff --git a/drivers/block/paride/pd.c b/drivers/block/paride/pd.c
index fea7e76..d48715b 100644
--- a/drivers/block/paride/pd.c
+++ b/drivers/block/paride/pd.c
@@ -722,6 +722,8 @@
 	int err = 0;
 
 	rq = blk_get_request(disk->gd->queue, READ, __GFP_WAIT);
+	if (IS_ERR(rq))
+		return PTR_ERR(rq);
 
 	rq->cmd_type = REQ_TYPE_SPECIAL;
 	rq->special = func;
diff --git a/drivers/block/pktcdvd.c b/drivers/block/pktcdvd.c
index 758ac44..09e628da 100644
--- a/drivers/block/pktcdvd.c
+++ b/drivers/block/pktcdvd.c
@@ -704,6 +704,8 @@
 
 	rq = blk_get_request(q, (cgc->data_direction == CGC_DATA_WRITE) ?
 			     WRITE : READ, __GFP_WAIT);
+	if (IS_ERR(rq))
+		return PTR_ERR(rq);
 	blk_rq_set_block_pc(rq);
 
 	if (cgc->buflen) {
diff --git a/drivers/block/sx8.c b/drivers/block/sx8.c
index d5e2d12..5d55285 100644
--- a/drivers/block/sx8.c
+++ b/drivers/block/sx8.c
@@ -568,7 +568,7 @@
 		return NULL;
 
 	rq = blk_get_request(host->oob_q, WRITE /* bogus */, GFP_KERNEL);
-	if (!rq) {
+	if (IS_ERR(rq)) {
 		spin_lock_irqsave(&host->lock, flags);
 		carm_put_request(host, crq);
 		spin_unlock_irqrestore(&host->lock, flags);
diff --git a/drivers/cdrom/cdrom.c b/drivers/cdrom/cdrom.c
index 898b84b..5d28a45 100644
--- a/drivers/cdrom/cdrom.c
+++ b/drivers/cdrom/cdrom.c
@@ -2180,8 +2180,8 @@
 		len = nr * CD_FRAMESIZE_RAW;
 
 		rq = blk_get_request(q, READ, GFP_KERNEL);
-		if (!rq) {
-			ret = -ENOMEM;
+		if (IS_ERR(rq)) {
+			ret = PTR_ERR(rq);
 			break;
 		}
 		blk_rq_set_block_pc(rq);
diff --git a/drivers/ide/ide-park.c b/drivers/ide/ide-park.c
index f41558a..ca95860 100644
--- a/drivers/ide/ide-park.c
+++ b/drivers/ide/ide-park.c
@@ -46,7 +46,7 @@
 	 * timeout has expired, so power management will be reenabled.
 	 */
 	rq = blk_get_request(q, READ, GFP_NOWAIT);
-	if (unlikely(!rq))
+	if (IS_ERR(rq))
 		goto out;
 
 	rq->cmd[0] = REQ_UNPARK_HEADS;
diff --git a/drivers/scsi/device_handler/scsi_dh_alua.c b/drivers/scsi/device_handler/scsi_dh_alua.c
index 7bcf67e..e99507e 100644
--- a/drivers/scsi/device_handler/scsi_dh_alua.c
+++ b/drivers/scsi/device_handler/scsi_dh_alua.c
@@ -115,7 +115,7 @@
 
 	rq = blk_get_request(q, rw, GFP_NOIO);
 
-	if (!rq) {
+	if (IS_ERR(rq)) {
 		sdev_printk(KERN_INFO, sdev,
 			    "%s: blk_get_request failed\n", __func__);
 		return NULL;
diff --git a/drivers/scsi/device_handler/scsi_dh_emc.c b/drivers/scsi/device_handler/scsi_dh_emc.c
index 6f07f7fe..8476538 100644
--- a/drivers/scsi/device_handler/scsi_dh_emc.c
+++ b/drivers/scsi/device_handler/scsi_dh_emc.c
@@ -275,7 +275,7 @@
 
 	rq = blk_get_request(sdev->request_queue,
 			(cmd != INQUIRY) ? WRITE : READ, GFP_NOIO);
-	if (!rq) {
+	if (IS_ERR(rq)) {
 		sdev_printk(KERN_INFO, sdev, "get_req: blk_get_request failed");
 		return NULL;
 	}
diff --git a/drivers/scsi/device_handler/scsi_dh_hp_sw.c b/drivers/scsi/device_handler/scsi_dh_hp_sw.c
index e9d9fea..4ee2759 100644
--- a/drivers/scsi/device_handler/scsi_dh_hp_sw.c
+++ b/drivers/scsi/device_handler/scsi_dh_hp_sw.c
@@ -117,7 +117,7 @@
 
 retry:
 	req = blk_get_request(sdev->request_queue, WRITE, GFP_NOIO);
-	if (!req)
+	if (IS_ERR(req))
 		return SCSI_DH_RES_TEMP_UNAVAIL;
 
 	blk_rq_set_block_pc(req);
@@ -247,7 +247,7 @@
 	struct request *req;
 
 	req = blk_get_request(h->sdev->request_queue, WRITE, GFP_ATOMIC);
-	if (!req)
+	if (IS_ERR(req))
 		return SCSI_DH_RES_TEMP_UNAVAIL;
 
 	blk_rq_set_block_pc(req);
diff --git a/drivers/scsi/device_handler/scsi_dh_rdac.c b/drivers/scsi/device_handler/scsi_dh_rdac.c
index 826069d..1b5bc92 100644
--- a/drivers/scsi/device_handler/scsi_dh_rdac.c
+++ b/drivers/scsi/device_handler/scsi_dh_rdac.c
@@ -274,7 +274,7 @@
 
 	rq = blk_get_request(q, rw, GFP_NOIO);
 
-	if (!rq) {
+	if (IS_ERR(rq)) {
 		sdev_printk(KERN_INFO, sdev,
 				"get_rdac_req: blk_get_request failed.\n");
 		return NULL;
diff --git a/drivers/scsi/osd/osd_initiator.c b/drivers/scsi/osd/osd_initiator.c
index 5f4cbf0..fd19fd8 100644
--- a/drivers/scsi/osd/osd_initiator.c
+++ b/drivers/scsi/osd/osd_initiator.c
@@ -1567,8 +1567,8 @@
 		struct request *req;
 
 		req = blk_get_request(q, has_write ? WRITE : READ, flags);
-		if (unlikely(!req))
-			return ERR_PTR(-ENOMEM);
+		if (IS_ERR(req))
+			return req;
 
 		blk_rq_set_block_pc(req);
 		return req;
diff --git a/drivers/scsi/osst.c b/drivers/scsi/osst.c
index 0727ea7..dff37a25 100644
--- a/drivers/scsi/osst.c
+++ b/drivers/scsi/osst.c
@@ -362,7 +362,7 @@
 	int write = (data_direction == DMA_TO_DEVICE);
 
 	req = blk_get_request(SRpnt->stp->device->request_queue, write, GFP_KERNEL);
-	if (!req)
+	if (IS_ERR(req))
 		return DRIVER_ERROR << 24;
 
 	blk_rq_set_block_pc(req);
diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
index 5db8454..a2c3d3d 100644
--- a/drivers/scsi/scsi_error.c
+++ b/drivers/scsi/scsi_error.c
@@ -1960,6 +1960,8 @@
 	 * request becomes available
 	 */
 	req = blk_get_request(sdev->request_queue, READ, GFP_KERNEL);
+	if (IS_ERR(req))
+		return;
 
 	blk_rq_set_block_pc(req);
 
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index d837dc1..1f2bae4 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -221,7 +221,7 @@
 	int ret = DRIVER_ERROR << 24;
 
 	req = blk_get_request(sdev->request_queue, write, __GFP_WAIT);
-	if (!req)
+	if (IS_ERR(req))
 		return ret;
 	blk_rq_set_block_pc(req);
 
diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 01cf888..6035444 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -1711,9 +1711,9 @@
 	}
 
 	rq = blk_get_request(q, rw, GFP_ATOMIC);
-	if (!rq) {
+	if (IS_ERR(rq)) {
 		kfree(long_cmdp);
-		return -ENOMEM;
+		return PTR_ERR(rq);
 	}
 
 	blk_rq_set_block_pc(rq);
diff --git a/drivers/scsi/st.c b/drivers/scsi/st.c
index aff9689..59db5bf 100644
--- a/drivers/scsi/st.c
+++ b/drivers/scsi/st.c
@@ -490,7 +490,7 @@
 
 	req = blk_get_request(SRpnt->stp->device->request_queue, write,
 			      GFP_KERNEL);
-	if (!req)
+	if (IS_ERR(req))
 		return DRIVER_ERROR << 24;
 
 	blk_rq_set_block_pc(req);
diff --git a/drivers/target/target_core_pscsi.c b/drivers/target/target_core_pscsi.c
index 943b1db..70d9f6d 100644
--- a/drivers/target/target_core_pscsi.c
+++ b/drivers/target/target_core_pscsi.c
@@ -1050,7 +1050,7 @@
 		req = blk_get_request(pdv->pdv_sd->request_queue,
 				(data_direction == DMA_TO_DEVICE),
 				GFP_KERNEL);
-		if (!req) {
+		if (IS_ERR(req)) {
 			pr_err("PSCSI: blk_get_request() failed\n");
 			ret = TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
 			goto fail;
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 6d72746..cc8d68a 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -50,32 +50,22 @@
 EXPORT_SYMBOL(I_BDEV);
 
 /*
- * Move the inode from its current bdi to a new bdi. If the inode is dirty we
- * need to move it onto the dirty list of @dst so that the inode is always on
- * the right list.
+ * Move the inode from its current bdi to a new bdi.  Make sure the inode
+ * is clean before moving so that it doesn't linger on the old bdi.
  */
 static void bdev_inode_switch_bdi(struct inode *inode,
 			struct backing_dev_info *dst)
 {
-	struct backing_dev_info *old = inode->i_data.backing_dev_info;
-	bool wakeup_bdi = false;
-
-	if (unlikely(dst == old))		/* deadlock avoidance */
-		return;
-	bdi_lock_two(&old->wb, &dst->wb);
-	spin_lock(&inode->i_lock);
-	inode->i_data.backing_dev_info = dst;
-	if (inode->i_state & I_DIRTY) {
-		if (bdi_cap_writeback_dirty(dst) && !wb_has_dirty_io(&dst->wb))
-			wakeup_bdi = true;
-		list_move(&inode->i_wb_list, &dst->wb.b_dirty);
+	while (true) {
+		spin_lock(&inode->i_lock);
+		if (!(inode->i_state & I_DIRTY)) {
+			inode->i_data.backing_dev_info = dst;
+			spin_unlock(&inode->i_lock);
+			return;
+		}
+		spin_unlock(&inode->i_lock);
+		WARN_ON_ONCE(write_inode_now(inode, true));
 	}
-	spin_unlock(&inode->i_lock);
-	spin_unlock(&old->wb.list_lock);
-	spin_unlock(&dst->wb.list_lock);
-
-	if (wakeup_bdi)
-		bdi_wakeup_thread_delayed(dst);
 }
 
 /* Kill _all_ buffers and pagecache , dirty or not.. */
@@ -1173,8 +1163,6 @@
 			if (!ret) {
 				bd_set_size(bdev,(loff_t)get_capacity(disk)<<9);
 				bdi = blk_get_backing_dev_info(bdev);
-				if (bdi == NULL)
-					bdi = &default_backing_dev_info;
 				bdev_inode_switch_bdi(bdev->bd_inode, bdi);
 			}
 
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index a1d36e6..7e221b0 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1699,7 +1699,7 @@
 		if (!device->bdev)
 			continue;
 		bdi = blk_get_backing_dev_info(device->bdev);
-		if (bdi && bdi_congested(bdi, bdi_bits)) {
+		if (bdi_congested(bdi, bdi_bits)) {
 			ret = 1;
 			break;
 		}
diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index cd7b8ca..497fcde 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -1678,8 +1678,6 @@
 	btp->bt_dev =  bdev->bd_dev;
 	btp->bt_bdev = bdev;
 	btp->bt_bdi = blk_get_backing_dev_info(bdev);
-	if (!btp->bt_bdi)
-		goto error;
 
 	if (xfs_setsize_buftarg_early(btp, bdev))
 		goto error;
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index e488e94..5da6012 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -28,12 +28,10 @@
  * Bits in backing_dev_info.state
  */
 enum bdi_state {
-	BDI_wb_alloc,		/* Default embedded wb allocated */
 	BDI_async_congested,	/* The async (write) queue is getting full */
 	BDI_sync_congested,	/* The sync queue is getting full */
 	BDI_registered,		/* bdi_register() was done */
 	BDI_writeback_running,	/* Writeback is in progress */
-	BDI_unused,		/* Available bits start here */
 };
 
 typedef int (congested_fn)(void *, int);
@@ -50,7 +48,6 @@
 
 struct bdi_writeback {
 	struct backing_dev_info *bdi;	/* our parent bdi */
-	unsigned int nr;
 
 	unsigned long last_old_flush;	/* last old data flush */
 
@@ -124,7 +121,6 @@
 void bdi_writeback_workfn(struct work_struct *work);
 int bdi_has_dirty_io(struct backing_dev_info *bdi);
 void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi);
-void bdi_lock_two(struct bdi_writeback *wb1, struct bdi_writeback *wb2);
 
 extern spinlock_t bdi_lock;
 extern struct list_head bdi_list;
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 518b465..e267bf0 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -865,7 +865,7 @@
 
 static inline struct request_queue *bdev_get_queue(struct block_device *bdev)
 {
-	return bdev->bd_disk->queue;
+	return bdev->bd_disk->queue;	/* this is never NULL */
 }
 
 /*
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 1706cbb..7d63d5e 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -40,7 +40,7 @@
 /* bdi_wq serves all asynchronous writeback tasks */
 struct workqueue_struct *bdi_wq;
 
-void bdi_lock_two(struct bdi_writeback *wb1, struct bdi_writeback *wb2)
+static void bdi_lock_two(struct bdi_writeback *wb1, struct bdi_writeback *wb2)
 {
 	if (wb1 < wb2) {
 		spin_lock(&wb1->list_lock);
@@ -376,13 +376,7 @@
 	mod_delayed_work(bdi_wq, &bdi->wb.dwork, 0);
 	flush_delayed_work(&bdi->wb.dwork);
 	WARN_ON(!list_empty(&bdi->work_list));
-
-	/*
-	 * This shouldn't be necessary unless @bdi for some reason has
-	 * unflushed dirty IO after work_list is drained.  Do it anyway
-	 * just in case.
-	 */
-	cancel_delayed_work_sync(&bdi->wb.dwork);
+	WARN_ON(delayed_work_pending(&bdi->wb.dwork));
 }
 
 /*
@@ -402,21 +396,15 @@
 
 void bdi_unregister(struct backing_dev_info *bdi)
 {
-	struct device *dev = bdi->dev;
-
-	if (dev) {
+	if (bdi->dev) {
 		bdi_set_min_ratio(bdi, 0);
 		trace_writeback_bdi_unregister(bdi);
 		bdi_prune_sb(bdi);
 
 		bdi_wb_shutdown(bdi);
 		bdi_debug_unregister(bdi);
-
-		spin_lock_bh(&bdi->wb_lock);
+		device_unregister(bdi->dev);
 		bdi->dev = NULL;
-		spin_unlock_bh(&bdi->wb_lock);
-
-		device_unregister(dev);
 	}
 }
 EXPORT_SYMBOL(bdi_unregister);
@@ -487,8 +475,17 @@
 	int i;
 
 	/*
-	 * Splice our entries to the default_backing_dev_info, if this
-	 * bdi disappears
+	 * Splice our entries to the default_backing_dev_info.  This
+	 * condition shouldn't happen.  @wb must be empty at this point and
+	 * dirty inodes on it might cause other issues.  This workaround is
+	 * added by ce5f8e779519 ("writeback: splice dirty inode entries to
+	 * default bdi on bdi_destroy()") without root-causing the issue.
+	 *
+	 * http://lkml.kernel.org/g/1253038617-30204-11-git-send-email-jens.axboe@oracle.com
+	 * http://thread.gmane.org/gmane.linux.file-systems/35341/focus=35350
+	 *
+	 * We should probably add WARN_ON() to find out whether it still
+	 * happens and track it down if so.
 	 */
 	if (bdi_has_dirty_io(bdi)) {
 		struct bdi_writeback *dst = &default_backing_dev_info.wb;
@@ -503,12 +500,7 @@
 
 	bdi_unregister(bdi);
 
-	/*
-	 * If bdi_unregister() had already been called earlier, the dwork
-	 * could still be pending because bdi_prune_sb() can race with the
-	 * bdi_wakeup_thread_delayed() calls from __mark_inode_dirty().
-	 */
-	cancel_delayed_work_sync(&bdi->wb.dwork);
+	WARN_ON(delayed_work_pending(&bdi->wb.dwork));
 
 	for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
 		percpu_counter_destroy(&bdi->bdi_stat[i]);