[PATCH 06/12] xen-blkfront: add callbacks for PM suspend and hibernation

[Anchal Agarwal <anchalag@amazon.com>]

From: Munehisa Kamata <kamatam@amazon.com>

S4 power transition states are much different than xen
suspend/resume. Former is visible to the guest and frontend drivers should
be aware of the state transitions and should be able to take appropriate
actions when needed. In transition to S4 we need to make sure that at least
all the in-flight blkif requests get completed, since they probably contain
bits of the guest's memory image and that's not going to get saved any
other way. Hence, re-issuing of in-flight requests as in case of xen resume
will not work here. This is in contrast to xen-suspend where we need to
freeze with as little processing as possible to avoid dirtying RAM late in
the migration cycle and we know that in-flight data can wait.

Add freeze, thaw and restore callbacks for PM suspend and hibernation
support. All frontend drivers that needs to use PM_HIBERNATION/PM_SUSPEND
events, need to implement these xenbus_driver callbacks. The freeze handler
stops block-layer queue and disconnect the frontend from the backend while
freeing ring_info and associated resources. Before disconnecting from the
backend, we need to prevent any new IO from being queued and wait for existing
IO to complete. Freeze/unfreeze of the queues will guarantee that there are no
requests in use on the shared ring. However, for sanity we should check
state of the ring before disconnecting to make sure that there are no
outstanding requests to be processed on the ring. The restore handler
re-allocates ring_info, unquiesces and unfreezes the queue and re-connect to
the backend, so that rest of the kernel can continue to use the block device
transparently.

Note:For older backends,if a backend doesn't have commit'12ea729645ace'
xen/blkback: unmap all persistent grants when frontend gets disconnected,
the frontend may see massive amount of grant table warning when freeing
resources.
[   36.852659] deferring g.e. 0xf9 (pfn 0xffffffffffffffff)
[   36.855089] xen:grant_table: WARNING:e.g. 0x112 still in use!

In this case, persistent grants would need to be disabled.

[Anchal Changelog: Removed timeout/request during blkfront freeze.
Reworked the whole patch to work with blk-mq and incorporate upstream's
comments]

Signed-off-by: Anchal Agarwal <anchalag@amazon.com>
Signed-off-by: Munehisa Kamata <kamatam@amazon.com>
---
 drivers/block/xen-blkfront.c | 122 +++++++++++++++++++++++++++++++++--
 1 file changed, 115 insertions(+), 7 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 3b889ea950c2..464863ed7093 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -48,6 +48,8 @@
 #include <linux/list.h>
 #include <linux/workqueue.h>
 #include <linux/sched/mm.h>
+#include <linux/completion.h>
+#include <linux/delay.h>
 
 #include <xen/xen.h>
 #include <xen/xenbus.h>
@@ -80,6 +82,8 @@ enum blkif_state {
 	BLKIF_STATE_DISCONNECTED,
 	BLKIF_STATE_CONNECTED,
 	BLKIF_STATE_SUSPENDED,
+	BLKIF_STATE_FREEZING,
+	BLKIF_STATE_FROZEN
 };
 
 struct grant {
@@ -219,6 +223,7 @@ struct blkfront_info
 	struct list_head requests;
 	struct bio_list bio_list;
 	struct list_head info_list;
+	struct completion wait_backend_disconnected;
 };
 
 static unsigned int nr_minors;
@@ -1005,6 +1010,7 @@ static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size,
 	info->sector_size = sector_size;
 	info->physical_sector_size = physical_sector_size;
 	blkif_set_queue_limits(info);
+	init_completion(&info->wait_backend_disconnected);
 
 	return 0;
 }
@@ -1057,7 +1063,7 @@ static int xen_translate_vdev(int vdevice, int *minor, unsigned int *offset)
 		case XEN_SCSI_DISK5_MAJOR:
 		case XEN_SCSI_DISK6_MAJOR:
 		case XEN_SCSI_DISK7_MAJOR:
-			*offset = (*minor / PARTS_PER_DISK) + 
+			*offset = (*minor / PARTS_PER_DISK) +
 				((major - XEN_SCSI_DISK1_MAJOR + 1) * 16) +
 				EMULATED_SD_DISK_NAME_OFFSET;
 			*minor = *minor +
@@ -1072,7 +1078,7 @@ static int xen_translate_vdev(int vdevice, int *minor, unsigned int *offset)
 		case XEN_SCSI_DISK13_MAJOR:
 		case XEN_SCSI_DISK14_MAJOR:
 		case XEN_SCSI_DISK15_MAJOR:
-			*offset = (*minor / PARTS_PER_DISK) + 
+			*offset = (*minor / PARTS_PER_DISK) +
 				((major - XEN_SCSI_DISK8_MAJOR + 8) * 16) +
 				EMULATED_SD_DISK_NAME_OFFSET;
 			*minor = *minor +
@@ -1353,6 +1359,8 @@ static void blkif_free(struct blkfront_info *info, int suspend)
 	unsigned int i;
 	struct blkfront_ring_info *rinfo;
 
+	if (info->connected == BLKIF_STATE_FREEZING)
+		goto free_rings;
 	/* Prevent new requests being issued until we fix things up. */
 	info->connected = suspend ?
 		BLKIF_STATE_SUSPENDED : BLKIF_STATE_DISCONNECTED;
@@ -1360,6 +1368,7 @@ static void blkif_free(struct blkfront_info *info, int suspend)
 	if (info->rq)
 		blk_mq_stop_hw_queues(info->rq);
 
+free_rings:
 	for_each_rinfo(info, rinfo, i)
 		blkif_free_ring(rinfo);
 
@@ -1563,8 +1572,10 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
 	struct blkfront_ring_info *rinfo = (struct blkfront_ring_info *)dev_id;
 	struct blkfront_info *info = rinfo->dev_info;
 
-	if (unlikely(info->connected != BLKIF_STATE_CONNECTED))
-		return IRQ_HANDLED;
+	if (unlikely(info->connected != BLKIF_STATE_CONNECTED
+		    && info->connected != BLKIF_STATE_FREEZING)){
+	    return IRQ_HANDLED;
+	}
 
 	spin_lock_irqsave(&rinfo->ring_lock, flags);
  again:
@@ -2027,6 +2038,7 @@ static int blkif_recover(struct blkfront_info *info)
 	unsigned int segs;
 	struct blkfront_ring_info *rinfo;
 
+	bool frozen = info->connected == BLKIF_STATE_FROZEN;
 	blkfront_gather_backend_features(info);
 	/* Reset limits changed by blk_mq_update_nr_hw_queues(). */
 	blkif_set_queue_limits(info);
@@ -2048,6 +2060,9 @@ static int blkif_recover(struct blkfront_info *info)
 		kick_pending_request_queues(rinfo);
 	}
 
+	if (frozen)
+		return 0;
+
 	list_for_each_entry_safe(req, n, &info->requests, queuelist) {
 		/* Requeue pending requests (flush or discard) */
 		list_del_init(&req->queuelist);
@@ -2364,6 +2379,7 @@ static void blkfront_connect(struct blkfront_info *info)
 
 		return;
 	case BLKIF_STATE_SUSPENDED:
+	case BLKIF_STATE_FROZEN:
 		/*
 		 * If we are recovering from suspension, we need to wait
 		 * for the backend to announce it's features before
@@ -2481,12 +2497,36 @@ static void blkback_changed(struct xenbus_device *dev,
 		break;
 
 	case XenbusStateClosed:
-		if (dev->state == XenbusStateClosed)
+		if (dev->state == XenbusStateClosed) {
+			if (info->connected == BLKIF_STATE_FREEZING) {
+				blkif_free(info, 0);
+				info->connected = BLKIF_STATE_FROZEN;
+				complete(&info->wait_backend_disconnected);
+				break;
+			}
+
 			break;
+		}
+
+		/*
+		 * We may somehow receive backend's Closed again while thawing
+		 * or restoring and it causes thawing or restoring to fail.
+		 * Ignore such unexpected state regardless of the backend state.
+		 */
+		if (info->connected == BLKIF_STATE_FROZEN) {
+			dev_dbg(&dev->dev,
+					"ignore the backend's Closed state: %s",
+					dev->nodename);
+			break;
+		}
 		/* fall through */
 	case XenbusStateClosing:
-		if (info)
-			blkfront_closing(info);
+		if (info) {
+			if (info->connected == BLKIF_STATE_FREEZING)
+				xenbus_frontend_closed(dev);
+			else
+				blkfront_closing(info);
+		}
 		break;
 	}
 }
@@ -2630,6 +2670,71 @@ static void blkif_release(struct gendisk *disk, fmode_t mode)
 	mutex_unlock(&blkfront_mutex);
 }
 
+static int blkfront_freeze(struct xenbus_device *dev)
+{
+	unsigned int i;
+	struct blkfront_info *info = dev_get_drvdata(&dev->dev);
+	struct blkfront_ring_info *rinfo;
+	/* This would be reasonable timeout as used in xenbus_dev_shutdown() */
+	unsigned int timeout = 5 * HZ;
+	unsigned long flags;
+	int err = 0;
+
+	info->connected = BLKIF_STATE_FREEZING;
+
+	blk_mq_freeze_queue(info->rq);
+	blk_mq_quiesce_queue(info->rq);
+
+	for_each_rinfo(info, rinfo, i) {
+	    /* No more gnttab callback work. */
+	    gnttab_cancel_free_callback(&rinfo->callback);
+	    /* Flush gnttab callback work. Must be done with no locks held. */
+	    flush_work(&rinfo->work);
+	}
+
+	for_each_rinfo(info, rinfo, i) {
+	    spin_lock_irqsave(&rinfo->ring_lock, flags);
+	    if (RING_FULL(&rinfo->ring)
+		    || RING_HAS_UNCONSUMED_RESPONSES(&rinfo->ring)) {
+		xenbus_dev_error(dev, err, "Hibernation Failed.
+			The ring is still busy");
+		info->connected = BLKIF_STATE_CONNECTED;
+		spin_unlock_irqrestore(&rinfo->ring_lock, flags);
+		return -EBUSY;
+	}
+	    spin_unlock_irqrestore(&rinfo->ring_lock, flags);
+	}
+	/* Kick the backend to disconnect */
+	xenbus_switch_state(dev, XenbusStateClosing);
+
+	/*
+	 * We don't want to move forward before the frontend is diconnected
+	 * from the backend cleanly.
+	 */
+	timeout = wait_for_completion_timeout(&info->wait_backend_disconnected,
+					      timeout);
+	if (!timeout) {
+		err = -EBUSY;
+		xenbus_dev_error(dev, err, "Freezing timed out;"
+				 "the device may become inconsistent state");
+	}
+
+	return err;
+}
+
+static int blkfront_restore(struct xenbus_device *dev)
+{
+	struct blkfront_info *info = dev_get_drvdata(&dev->dev);
+	int err = 0;
+
+	err = talk_to_blkback(dev, info);
+	blk_mq_unquiesce_queue(info->rq);
+	blk_mq_unfreeze_queue(info->rq);
+	if (!err)
+	    blk_mq_update_nr_hw_queues(&info->tag_set, info->nr_rings);
+	return err;
+}
+
 static const struct block_device_operations xlvbd_block_fops =
 {
 	.owner = THIS_MODULE,
@@ -2653,6 +2758,9 @@ static struct xenbus_driver blkfront_driver = {
 	.resume = blkfront_resume,
 	.otherend_changed = blkback_changed,
 	.is_ready = blkfront_is_ready,
+	.freeze = blkfront_freeze,
+	.thaw = blkfront_restore,
+	.restore = blkfront_restore
 };
 
 static void purge_persistent_grants(struct blkfront_info *info)
-- 
2.24.1.AMZN