Merge branch 'for-linus' of git://git.kernel.dk/linux-block

Pull block bits from Jens Axboe:
 "As vacation is coming up, thought I'd better get rid of my pending
  changes in my for-linus branch for this iteration.  It contains:

   - Two patches for mtip32xx.  Killing a non-compliant sysfs interface
     and moving it to debugfs, where it belongs.

   - A few patches from Asias.  Two legit bug fixes, and one killing an
     interface that is no longer in use.

   - A patch from Jan, making the annoying partition ioctl warning a bit
     less annoying, by restricting it to !CAP_SYS_RAWIO only.

   - Three bug fixes for drbd from Lars Ellenberg.

   - A fix for an old regression for umem, it hasn't really worked since
     the plugging scheme was changed in 3.0.

   - A few fixes from Tejun.

   - A splice fix from Eric Dumazet, fixing an issue with pipe
     resizing."

* 'for-linus' of git://git.kernel.dk/linux-block:
  scsi: Silence unnecessary warnings about ioctl to partition
  block: Drop dead function blk_abort_queue()
  block: Mitigate lock unbalance caused by lock switching
  block: Avoid missed wakeup in request waitqueue
  umem: fix up unplugging
  splice: fix racy pipe->buffers uses
  drbd: fix null pointer dereference with on-congestion policy when diskless
  drbd: fix list corruption by failing but already aborted reads
  drbd: fix access of unallocated pages and kernel panic
  xen/blkfront: Add WARN to deal with misbehaving backends.
  blkcg: drop local variable @q from blkg_destroy()
  mtip32xx: Create debugfs entries for troubleshooting
  mtip32xx: Remove 'registers' and 'flags' from sysfs
  blkcg: fix blkg_alloc() failure path
  block: blkcg_policy_cfq shouldn't be used if !CONFIG_CFQ_GROUP_IOSCHED
  block: fix return value on cfq_init() failure
  mtip32xx: Remove version.h header file inclusion
  xen/blkback: Copy id field when doing BLKIF_DISCARD.

7 files changed, 261 insertions, 87 deletions

diff --git a/drivers/block/drbd/drbd_bitmap.c b/drivers/block/drbd/drbd_bitmap.c
index b5c5ff53cb57..fcb956bb4b4c 100644
--- a/drivers/block/drbd/drbd_bitmap.c
+++ b/drivers/block/drbd/drbd_bitmap.c
@@ -1475,10 +1475,17 @@ void _drbd_bm_set_bits(struct drbd_conf *mdev, const unsigned long s, const unsi
 		first_word = 0;
 		spin_lock_irq(&b->bm_lock);
 	}
-
 	/* last page (respectively only page, for first page == last page) */
 	last_word = MLPP(el >> LN2_BPL);
-	bm_set_full_words_within_one_page(mdev->bitmap, last_page, first_word, last_word);
+
+	/* consider bitmap->bm_bits = 32768, bitmap->bm_number_of_pages = 1. (or multiples).
+	 * ==> e = 32767, el = 32768, last_page = 2,
+	 * and now last_word = 0.
+	 * We do not want to touch last_page in this case,
+	 * as we did not allocate it, it is not present in bitmap->bm_pages.
+	 */
+	if (last_word)
+		bm_set_full_words_within_one_page(mdev->bitmap, last_page, first_word, last_word);
 
 	/* possibly trailing bits.
 	 * example: (e & 63) == 63, el will be e+1.
diff --git a/drivers/block/drbd/drbd_req.c b/drivers/block/drbd/drbd_req.c
index 9c5c84946b05..8e93a6ac9bb6 100644
--- a/drivers/block/drbd/drbd_req.c
+++ b/drivers/block/drbd/drbd_req.c
@@ -472,12 +472,17 @@ int __req_mod(struct drbd_request *req, enum drbd_req_event what,
 		req->rq_state |= RQ_LOCAL_COMPLETED;
 		req->rq_state &= ~RQ_LOCAL_PENDING;
 
-		D_ASSERT(!(req->rq_state & RQ_NET_MASK));
+		if (req->rq_state & RQ_LOCAL_ABORTED) {
+			_req_may_be_done(req, m);
+			break;
+		}
 
 		__drbd_chk_io_error(mdev, false);
 
 	goto_queue_for_net_read:
 
+		D_ASSERT(!(req->rq_state & RQ_NET_MASK));
+
 		/* no point in retrying if there is no good remote data,
 		 * or we have no connection. */
 		if (mdev->state.pdsk != D_UP_TO_DATE) {
@@ -765,6 +770,40 @@ static int drbd_may_do_local_read(struct drbd_conf *mdev, sector_t sector, int s
 	return 0 == drbd_bm_count_bits(mdev, sbnr, ebnr);
 }
 
+static void maybe_pull_ahead(struct drbd_conf *mdev)
+{
+	int congested = 0;
+
+	/* If I don't even have good local storage, we can not reasonably try
+	 * to pull ahead of the peer. We also need the local reference to make
+	 * sure mdev->act_log is there.
+	 * Note: caller has to make sure that net_conf is there.
+	 */
+	if (!get_ldev_if_state(mdev, D_UP_TO_DATE))
+		return;
+
+	if (mdev->net_conf->cong_fill &&
+	    atomic_read(&mdev->ap_in_flight) >= mdev->net_conf->cong_fill) {
+		dev_info(DEV, "Congestion-fill threshold reached\n");
+		congested = 1;
+	}
+
+	if (mdev->act_log->used >= mdev->net_conf->cong_extents) {
+		dev_info(DEV, "Congestion-extents threshold reached\n");
+		congested = 1;
+	}
+
+	if (congested) {
+		queue_barrier(mdev); /* last barrier, after mirrored writes */
+
+		if (mdev->net_conf->on_congestion == OC_PULL_AHEAD)
+			_drbd_set_state(_NS(mdev, conn, C_AHEAD), 0, NULL);
+		else  /*mdev->net_conf->on_congestion == OC_DISCONNECT */
+			_drbd_set_state(_NS(mdev, conn, C_DISCONNECTING), 0, NULL);
+	}
+	put_ldev(mdev);
+}
+
 static int drbd_make_request_common(struct drbd_conf *mdev, struct bio *bio, unsigned long start_time)
 {
 	const int rw = bio_rw(bio);
@@ -972,29 +1011,8 @@ allocate_barrier:
 		_req_mod(req, queue_for_send_oos);
 
 	if (remote &&
-	    mdev->net_conf->on_congestion != OC_BLOCK && mdev->agreed_pro_version >= 96) {
-		int congested = 0;
-
-		if (mdev->net_conf->cong_fill &&
-		    atomic_read(&mdev->ap_in_flight) >= mdev->net_conf->cong_fill) {
-			dev_info(DEV, "Congestion-fill threshold reached\n");
-			congested = 1;
-		}
-
-		if (mdev->act_log->used >= mdev->net_conf->cong_extents) {
-			dev_info(DEV, "Congestion-extents threshold reached\n");
-			congested = 1;
-		}
-
-		if (congested) {
-			queue_barrier(mdev); /* last barrier, after mirrored writes */
-
-			if (mdev->net_conf->on_congestion == OC_PULL_AHEAD)
-				_drbd_set_state(_NS(mdev, conn, C_AHEAD), 0, NULL);
-			else  /*mdev->net_conf->on_congestion == OC_DISCONNECT */
-				_drbd_set_state(_NS(mdev, conn, C_DISCONNECTING), 0, NULL);
-		}
-	}
+	    mdev->net_conf->on_congestion != OC_BLOCK && mdev->agreed_pro_version >= 96)
+		maybe_pull_ahead(mdev);
 
 	spin_unlock_irq(&mdev->req_lock);
 	kfree(b); /* if someone else has beaten us to it... */
diff --git a/drivers/block/mtip32xx/mtip32xx.c b/drivers/block/mtip32xx/mtip32xx.c
index 264bc77dcb91..a8fddeb3d638 100644
--- a/drivers/block/mtip32xx/mtip32xx.c
+++ b/drivers/block/mtip32xx/mtip32xx.c
@@ -37,6 +37,7 @@
 #include <linux/kthread.h>
 #include <../drivers/ata/ahci.h>
 #include <linux/export.h>
+#include <linux/debugfs.h>
 #include "mtip32xx.h"
 
 #define HW_CMD_SLOT_SZ		(MTIP_MAX_COMMAND_SLOTS * 32)
@@ -85,6 +86,7 @@ static int instance;
  * allocated in mtip_init().
  */
 static int mtip_major;
+static struct dentry *dfs_parent;
 
 static DEFINE_SPINLOCK(rssd_index_lock);
 static DEFINE_IDA(rssd_index_ida);
@@ -2546,7 +2548,7 @@ static struct scatterlist *mtip_hw_get_scatterlist(struct driver_data *dd,
 }
 
 /*
- * Sysfs register/status dump.
+ * Sysfs status dump.
  *
  * @dev  Pointer to the device structure, passed by the kernrel.
  * @attr Pointer to the device_attribute structure passed by the kernel.
@@ -2555,45 +2557,68 @@ static struct scatterlist *mtip_hw_get_scatterlist(struct driver_data *dd,
  * return value
  *	The size, in bytes, of the data copied into buf.
  */
-static ssize_t mtip_hw_show_registers(struct device *dev,
+static ssize_t mtip_hw_show_status(struct device *dev,
 				struct device_attribute *attr,
 				char *buf)
 {
-	u32 group_allocated;
 	struct driver_data *dd = dev_to_disk(dev)->private_data;
 	int size = 0;
+
+	if (test_bit(MTIP_DDF_OVER_TEMP_BIT, &dd->dd_flag))
+		size += sprintf(buf, "%s", "thermal_shutdown\n");
+	else if (test_bit(MTIP_DDF_WRITE_PROTECT_BIT, &dd->dd_flag))
+		size += sprintf(buf, "%s", "write_protect\n");
+	else
+		size += sprintf(buf, "%s", "online\n");
+
+	return size;
+}
+
+static DEVICE_ATTR(status, S_IRUGO, mtip_hw_show_status, NULL);
+
+static ssize_t mtip_hw_read_registers(struct file *f, char __user *ubuf,
+				  size_t len, loff_t *offset)
+{
+	struct driver_data *dd =  (struct driver_data *)f->private_data;
+	char buf[MTIP_DFS_MAX_BUF_SIZE];
+	u32 group_allocated;
+	int size = *offset;
 	int n;
 
-	size += sprintf(&buf[size], "Hardware\n--------\n");
-	size += sprintf(&buf[size], "S ACTive      : [ 0x");
+	if (!len || size)
+		return 0;
+
+	if (size < 0)
+		return -EINVAL;
+
+	size += sprintf(&buf[size], "H/ S ACTive      : [ 0x");
 
 	for (n = dd->slot_groups-1; n >= 0; n--)
 		size += sprintf(&buf[size], "%08X ",
 					 readl(dd->port->s_active[n]));
 
 	size += sprintf(&buf[size], "]\n");
-	size += sprintf(&buf[size], "Command Issue : [ 0x");
+	size += sprintf(&buf[size], "H/ Command Issue : [ 0x");
 
 	for (n = dd->slot_groups-1; n >= 0; n--)
 		size += sprintf(&buf[size], "%08X ",
 					readl(dd->port->cmd_issue[n]));
 
 	size += sprintf(&buf[size], "]\n");
-	size += sprintf(&buf[size], "Completed     : [ 0x");
+	size += sprintf(&buf[size], "H/ Completed     : [ 0x");
 
 	for (n = dd->slot_groups-1; n >= 0; n--)
 		size += sprintf(&buf[size], "%08X ",
 				readl(dd->port->completed[n]));
 
 	size += sprintf(&buf[size], "]\n");
-	size += sprintf(&buf[size], "PORT IRQ STAT : [ 0x%08X ]\n",
+	size += sprintf(&buf[size], "H/ PORT IRQ STAT : [ 0x%08X ]\n",
 				readl(dd->port->mmio + PORT_IRQ_STAT));
-	size += sprintf(&buf[size], "HOST IRQ STAT : [ 0x%08X ]\n",
+	size += sprintf(&buf[size], "H/ HOST IRQ STAT : [ 0x%08X ]\n",
 				readl(dd->mmio + HOST_IRQ_STAT));
 	size += sprintf(&buf[size], "\n");
 
-	size += sprintf(&buf[size], "Local\n-----\n");
-	size += sprintf(&buf[size], "Allocated    : [ 0x");
+	size += sprintf(&buf[size], "L/ Allocated     : [ 0x");
 
 	for (n = dd->slot_groups-1; n >= 0; n--) {
 		if (sizeof(long) > sizeof(u32))
@@ -2605,7 +2630,7 @@ static ssize_t mtip_hw_show_registers(struct device *dev,
 	}
 	size += sprintf(&buf[size], "]\n");
 
-	size += sprintf(&buf[size], "Commands in Q: [ 0x");
+	size += sprintf(&buf[size], "L/ Commands in Q : [ 0x");
 
 	for (n = dd->slot_groups-1; n >= 0; n--) {
 		if (sizeof(long) > sizeof(u32))
@@ -2617,44 +2642,53 @@ static ssize_t mtip_hw_show_registers(struct device *dev,
 	}
 	size += sprintf(&buf[size], "]\n");
 
-	return size;
+	*offset = size <= len ? size : len;
+	size = copy_to_user(ubuf, buf, *offset);
+	if (size)
+		return -EFAULT;
+
+	return *offset;
 }
 
-static ssize_t mtip_hw_show_status(struct device *dev,
-				struct device_attribute *attr,
-				char *buf)
+static ssize_t mtip_hw_read_flags(struct file *f, char __user *ubuf,
+				  size_t len, loff_t *offset)
 {
-	struct driver_data *dd = dev_to_disk(dev)->private_data;
-	int size = 0;
+	struct driver_data *dd =  (struct driver_data *)f->private_data;
+	char buf[MTIP_DFS_MAX_BUF_SIZE];
+	int size = *offset;
 
-	if (test_bit(MTIP_DDF_OVER_TEMP_BIT, &dd->dd_flag))
-		size += sprintf(buf, "%s", "thermal_shutdown\n");
-	else if (test_bit(MTIP_DDF_WRITE_PROTECT_BIT, &dd->dd_flag))
-		size += sprintf(buf, "%s", "write_protect\n");
-	else
-		size += sprintf(buf, "%s", "online\n");
-
-	return size;
-}
+	if (!len || size)
+		return 0;
 
-static ssize_t mtip_hw_show_flags(struct device *dev,
-				struct device_attribute *attr,
-				char *buf)
-{
-	struct driver_data *dd = dev_to_disk(dev)->private_data;
-	int size = 0;
+	if (size < 0)
+		return -EINVAL;
 
-	size += sprintf(&buf[size], "Flag in port struct : [ %08lX ]\n",
+	size += sprintf(&buf[size], "Flag-port : [ %08lX ]\n",
 							dd->port->flags);
-	size += sprintf(&buf[size], "Flag in dd struct   : [ %08lX ]\n",
+	size += sprintf(&buf[size], "Flag-dd   : [ %08lX ]\n",
 							dd->dd_flag);
 
-	return size;
+	*offset = size <= len ? size : len;
+	size = copy_to_user(ubuf, buf, *offset);
+	if (size)
+		return -EFAULT;
+
+	return *offset;
 }
 
-static DEVICE_ATTR(registers, S_IRUGO, mtip_hw_show_registers, NULL);
-static DEVICE_ATTR(status, S_IRUGO, mtip_hw_show_status, NULL);
-static DEVICE_ATTR(flags, S_IRUGO, mtip_hw_show_flags, NULL);
+static const struct file_operations mtip_regs_fops = {
+	.owner  = THIS_MODULE,
+	.open   = simple_open,
+	.read   = mtip_hw_read_registers,
+	.llseek = no_llseek,
+};
+
+static const struct file_operations mtip_flags_fops = {
+	.owner  = THIS_MODULE,
+	.open   = simple_open,
+	.read   = mtip_hw_read_flags,
+	.llseek = no_llseek,
+};
 
 /*
  * Create the sysfs related attributes.
@@ -2671,15 +2705,9 @@ static int mtip_hw_sysfs_init(struct driver_data *dd, struct kobject *kobj)
 	if (!kobj || !dd)
 		return -EINVAL;
 
-	if (sysfs_create_file(kobj, &dev_attr_registers.attr))
-		dev_warn(&dd->pdev->dev,
-			"Error creating 'registers' sysfs entry\n");
 	if (sysfs_create_file(kobj, &dev_attr_status.attr))
 		dev_warn(&dd->pdev->dev,
 			"Error creating 'status' sysfs entry\n");
-	if (sysfs_create_file(kobj, &dev_attr_flags.attr))
-		dev_warn(&dd->pdev->dev,
-			"Error creating 'flags' sysfs entry\n");
 	return 0;
 }
 
@@ -2698,13 +2726,39 @@ static int mtip_hw_sysfs_exit(struct driver_data *dd, struct kobject *kobj)
 	if (!kobj || !dd)
 		return -EINVAL;
 
-	sysfs_remove_file(kobj, &dev_attr_registers.attr);
 	sysfs_remove_file(kobj, &dev_attr_status.attr);
-	sysfs_remove_file(kobj, &dev_attr_flags.attr);
 
 	return 0;
 }
 
+static int mtip_hw_debugfs_init(struct driver_data *dd)
+{
+	if (!dfs_parent)
+		return -1;
+
+	dd->dfs_node = debugfs_create_dir(dd->disk->disk_name, dfs_parent);
+	if (IS_ERR_OR_NULL(dd->dfs_node)) {
+		dev_warn(&dd->pdev->dev,
+			"Error creating node %s under debugfs\n",
+						dd->disk->disk_name);
+		dd->dfs_node = NULL;
+		return -1;
+	}
+
+	debugfs_create_file("flags", S_IRUGO, dd->dfs_node, dd,
+							&mtip_flags_fops);
+	debugfs_create_file("registers", S_IRUGO, dd->dfs_node, dd,
+							&mtip_regs_fops);
+
+	return 0;
+}
+
+static void mtip_hw_debugfs_exit(struct driver_data *dd)
+{
+	debugfs_remove_recursive(dd->dfs_node);
+}
+
+
 /*
  * Perform any init/resume time hardware setup
  *
@@ -3730,6 +3784,7 @@ skip_create_disk:
 		mtip_hw_sysfs_init(dd, kobj);
 		kobject_put(kobj);
 	}
+	mtip_hw_debugfs_init(dd);
 
 	if (dd->mtip_svc_handler) {
 		set_bit(MTIP_DDF_INIT_DONE_BIT, &dd->dd_flag);
@@ -3755,6 +3810,8 @@ start_service_thread:
 	return rv;
 
 kthread_run_error:
+	mtip_hw_debugfs_exit(dd);
+
 	/* Delete our gendisk. This also removes the device from /dev */
 	del_gendisk(dd->disk);
 
@@ -3805,6 +3862,7 @@ static int mtip_block_remove(struct driver_data *dd)
 			kobject_put(kobj);
 		}
 	}
+	mtip_hw_debugfs_exit(dd);
 
 	/*
 	 * Delete our gendisk structure. This also removes the device
@@ -4152,10 +4210,20 @@ static int __init mtip_init(void)
 	}
 	mtip_major = error;
 
+	if (!dfs_parent) {
+		dfs_parent = debugfs_create_dir("rssd", NULL);
+		if (IS_ERR_OR_NULL(dfs_parent)) {
+			printk(KERN_WARNING "Error creating debugfs parent\n");
+			dfs_parent = NULL;
+		}
+	}
+
 	/* Register our PCI operations. */
 	error = pci_register_driver(&mtip_pci_driver);
-	if (error)
+	if (error) {
+		debugfs_remove(dfs_parent);
 		unregister_blkdev(mtip_major, MTIP_DRV_NAME);
+	}
 
 	return error;
 }
@@ -4172,6 +4240,8 @@ static int __init mtip_init(void)
  */
 static void __exit mtip_exit(void)
 {
+	debugfs_remove_recursive(dfs_parent);
+
 	/* Release the allocated major block device number. */
 	unregister_blkdev(mtip_major, MTIP_DRV_NAME);
 
diff --git a/drivers/block/mtip32xx/mtip32xx.h b/drivers/block/mtip32xx/mtip32xx.h
index b2c88da26b2a..f51fc23d17bb 100644
--- a/drivers/block/mtip32xx/mtip32xx.h
+++ b/drivers/block/mtip32xx/mtip32xx.h
@@ -26,7 +26,6 @@
 #include <linux/ata.h>
 #include <linux/interrupt.h>
 #include <linux/genhd.h>
-#include <linux/version.h>
 
 /* Offset of Subsystem Device ID in pci confoguration space */
 #define PCI_SUBSYSTEM_DEVICEID	0x2E
@@ -111,6 +110,8 @@
  #define dbg_printk(format, arg...)
 #endif
 
+#define MTIP_DFS_MAX_BUF_SIZE 1024
+
 #define __force_bit2int (unsigned int __force)
 
 enum {
@@ -447,6 +448,8 @@ struct driver_data {
 	unsigned long dd_flag; /* NOTE: use atomic bit operations on this */
 
 	struct task_struct *mtip_svc_handler; /* task_struct of svc thd */
+
+	struct dentry *dfs_node;
 };
 
 #endif
diff --git a/drivers/block/umem.c b/drivers/block/umem.c
index aa2712060bfb..9a72277a31df 100644
--- a/drivers/block/umem.c
+++ b/drivers/block/umem.c
@@ -513,6 +513,44 @@ static void process_page(unsigned long data)
 	}
 }
 
+struct mm_plug_cb {
+	struct blk_plug_cb cb;
+	struct cardinfo *card;
+};
+
+static void mm_unplug(struct blk_plug_cb *cb)
+{
+	struct mm_plug_cb *mmcb = container_of(cb, struct mm_plug_cb, cb);
+
+	spin_lock_irq(&mmcb->card->lock);
+	activate(mmcb->card);
+	spin_unlock_irq(&mmcb->card->lock);
+	kfree(mmcb);
+}
+
+static int mm_check_plugged(struct cardinfo *card)
+{
+	struct blk_plug *plug = current->plug;
+	struct mm_plug_cb *mmcb;
+
+	if (!plug)
+		return 0;
+
+	list_for_each_entry(mmcb, &plug->cb_list, cb.list) {
+		if (mmcb->cb.callback == mm_unplug && mmcb->card == card)
+			return 1;
+	}
+	/* Not currently on the callback list */
+	mmcb = kmalloc(sizeof(*mmcb), GFP_ATOMIC);
+	if (!mmcb)
+		return 0;
+
+	mmcb->card = card;
+	mmcb->cb.callback = mm_unplug;
+	list_add(&mmcb->cb.list, &plug->cb_list);
+	return 1;
+}
+
 static void mm_make_request(struct request_queue *q, struct bio *bio)
 {
 	struct cardinfo *card = q->queuedata;
@@ -523,6 +561,8 @@ static void mm_make_request(struct request_queue *q, struct bio *bio)
 	*card->biotail = bio;
 	bio->bi_next = NULL;
 	card->biotail = &bio->bi_next;
+	if (bio->bi_rw & REQ_SYNC || !mm_check_plugged(card))
+		activate(card);
 	spin_unlock_irq(&card->lock);
 
 	return;
diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h
index 773cf27dc23f..9ad3b5ec1dc1 100644
--- a/drivers/block/xen-blkback/common.h
+++ b/drivers/block/xen-blkback/common.h
@@ -257,6 +257,7 @@ static inline void blkif_get_x86_32_req(struct blkif_request *dst,
 		break;
 	case BLKIF_OP_DISCARD:
 		dst->u.discard.flag = src->u.discard.flag;
+		dst->u.discard.id = src->u.discard.id;
 		dst->u.discard.sector_number = src->u.discard.sector_number;
 		dst->u.discard.nr_sectors = src->u.discard.nr_sectors;
 		break;
@@ -287,6 +288,7 @@ static inline void blkif_get_x86_64_req(struct blkif_request *dst,
 		break;
 	case BLKIF_OP_DISCARD:
 		dst->u.discard.flag = src->u.discard.flag;
+		dst->u.discard.id = src->u.discard.id;
 		dst->u.discard.sector_number = src->u.discard.sector_number;
 		dst->u.discard.nr_sectors = src->u.discard.nr_sectors;
 		break;
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 60eed4bdd2e4..e4fb3374dcd2 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -141,14 +141,36 @@ static int get_id_from_freelist(struct blkfront_info *info)
 	return free;
 }
 
-static void add_id_to_freelist(struct blkfront_info *info,
+static int add_id_to_freelist(struct blkfront_info *info,
 			       unsigned long id)
 {
+	if (info->shadow[id].req.u.rw.id != id)
+		return -EINVAL;
+	if (info->shadow[id].request == NULL)
+		return -EINVAL;
 	info->shadow[id].req.u.rw.id  = info->shadow_free;
 	info->shadow[id].request = NULL;
 	info->shadow_free = id;
+	return 0;
 }
 
+static const char *op_name(int op)
+{
+	static const char *const names[] = {
+		[BLKIF_OP_READ] = "read",
+		[BLKIF_OP_WRITE] = "write",
+		[BLKIF_OP_WRITE_BARRIER] = "barrier",
+		[BLKIF_OP_FLUSH_DISKCACHE] = "flush",
+		[BLKIF_OP_DISCARD] = "discard" };
+
+	if (op < 0 || op >= ARRAY_SIZE(names))
+		return "unknown";
+
+	if (!names[op])
+		return "reserved";
+
+	return names[op];
+}
 static int xlbd_reserve_minors(unsigned int minor, unsigned int nr)
 {
 	unsigned int end = minor + nr;
@@ -746,20 +768,36 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
 
 		bret = RING_GET_RESPONSE(&info->ring, i);
 		id   = bret->id;
+		/*
+		 * The backend has messed up and given us an id that we would
+		 * never have given to it (we stamp it up to BLK_RING_SIZE -
+		 * look in get_id_from_freelist.
+		 */
+		if (id >= BLK_RING_SIZE) {
+			WARN(1, "%s: response to %s has incorrect id (%ld)\n",
+			     info->gd->disk_name, op_name(bret->operation), id);
+			/* We can't safely get the 'struct request' as
+			 * the id is busted. */
+			continue;
+		}
 		req  = info->shadow[id].request;
 
 		if (bret->operation != BLKIF_OP_DISCARD)
 			blkif_completion(&info->shadow[id]);
 
-		add_id_to_freelist(info, id);
+		if (add_id_to_freelist(info, id)) {
+			WARN(1, "%s: response to %s (id %ld) couldn't be recycled!\n",
+			     info->gd->disk_name, op_name(bret->operation), id);
+			continue;
+		}
 
 		error = (bret->status == BLKIF_RSP_OKAY) ? 0 : -EIO;
 		switch (bret->operation) {
 		case BLKIF_OP_DISCARD:
 			if (unlikely(bret->status == BLKIF_RSP_EOPNOTSUPP)) {
 				struct request_queue *rq = info->rq;
-				printk(KERN_WARNING "blkfront: %s: discard op failed\n",
-					   info->gd->disk_name);
+				printk(KERN_WARNING "blkfront: %s: %s op failed\n",
+					   info->gd->disk_name, op_name(bret->operation));
 				error = -EOPNOTSUPP;
 				info->feature_discard = 0;
 				info->feature_secdiscard = 0;
@@ -771,18 +809,14 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
 		case BLKIF_OP_FLUSH_DISKCACHE:
 		case BLKIF_OP_WRITE_BARRIER:
 			if (unlikely(bret->status == BLKIF_RSP_EOPNOTSUPP)) {
-				printk(KERN_WARNING "blkfront: %s: write %s op failed\n",
-				       info->flush_op == BLKIF_OP_WRITE_BARRIER ?
-				       "barrier" :  "flush disk cache",
-				       info->gd->disk_name);
+				printk(KERN_WARNING "blkfront: %s: %s op failed\n",
+				       info->gd->disk_name, op_name(bret->operation));
 				error = -EOPNOTSUPP;
 			}
 			if (unlikely(bret->status == BLKIF_RSP_ERROR &&
 				     info->shadow[id].req.u.rw.nr_segments == 0)) {
-				printk(KERN_WARNING "blkfront: %s: empty write %s op failed\n",
-				       info->flush_op == BLKIF_OP_WRITE_BARRIER ?
-				       "barrier" :  "flush disk cache",
-				       info->gd->disk_name);
+				printk(KERN_WARNING "blkfront: %s: empty %s op failed\n",
+				       info->gd->disk_name, op_name(bret->operation));
 				error = -EOPNOTSUPP;
 			}
 			if (unlikely(error)) {