X-Git-Url: http://git.onelab.eu/?a=blobdiff_plain;f=drivers%2Fmd%2Fdm-snap.c;h=0821a2b68a73a98719cb931c82196a74bfe471d4;hb=refs%2Fheads%2Fvserver;hp=5487b7cca1f85a87a517f12bc41fb59e3920c5cf;hpb=76828883507a47dae78837ab5dec5a5b4513c667;p=linux-2.6.git

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 5487b7cca..0821a2b68 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -7,7 +7,6 @@
  */
 
 #include <linux/blkdev.h>
-#include <linux/config.h>
 #include <linux/ctype.h>
 #include <linux/device-mapper.h>
 #include <linux/fs.h>
@@ -23,6 +22,8 @@
 #include "dm-bio-list.h"
 #include "kcopyd.h"
 
+#define DM_MSG_PREFIX "snapshots"
+
 /*
  * The percentage increment we will wake up users at
  */
@@ -38,6 +39,9 @@
  */
 #define SNAPSHOT_PAGES 256
 
+static struct workqueue_struct *ksnapd;
+static void flush_queued_bios(struct work_struct *work);
+
 struct pending_exception {
 	struct exception e;
 
@@ -49,11 +53,26 @@ struct pending_exception {
 	struct bio_list snapshot_bios;
 
 	/*
-	 * Other pending_exceptions that are processing this
-	 * chunk.  When this list is empty, we know we can
-	 * complete the origins.
+	 * Short-term queue of pending exceptions prior to submission.
 	 */
-	struct list_head siblings;
+	struct list_head list;
+
+	/*
+	 * The primary pending_exception is the one that holds
+	 * the ref_count and the list of origin_bios for a
+	 * group of pending_exceptions.  It is always last to get freed.
+	 * These fields get set up when writing to the origin.
+	 */
+	struct pending_exception *primary_pe;
+
+	/*
+	 * Number of pending_exceptions processing this chunk.
+	 * When this drops to zero we must complete the origin bios.
+	 * If incrementing or decrementing this, hold pe->snap->lock for
+	 * the sibling concerned and not pe->primary_pe->snap->lock unless
+	 * they are the same.
+	 */
+	atomic_t ref_count;
 
 	/* Pointer back to snapshot context */
 	struct dm_snapshot *snap;
@@ -69,8 +88,8 @@ struct pending_exception {
  * Hash table mapping origin volumes to lists of snapshots and
  * a lock to protect it
  */
-static kmem_cache_t *exception_cache;
-static kmem_cache_t *pending_cache;
+static struct kmem_cache *exception_cache;
+static struct kmem_cache *pending_cache;
 static mempool_t *pending_pool;
 
 /*
@@ -102,7 +121,7 @@ static int init_origin_hash(void)
 	_origins = kmalloc(ORIGIN_HASH_SIZE * sizeof(struct list_head),
 			   GFP_KERNEL);
 	if (!_origins) {
-		DMERR("Device mapper: Snapshot: unable to allocate memory");
+		DMERR("unable to allocate memory");
 		return -ENOMEM;
 	}
 
@@ -209,7 +228,7 @@ static int init_exception_table(struct exception_table *et, uint32_t size)
 	return 0;
 }
 
-static void exit_exception_table(struct exception_table *et, kmem_cache_t *mem)
+static void exit_exception_table(struct exception_table *et, struct kmem_cache *mem)
 {
 	struct list_head *slot;
 	struct exception *ex, *next;
@@ -371,13 +390,46 @@ static inline ulong round_up(ulong n, ulong size)
 	return (n + size) & ~size;
 }
 
-static void read_snapshot_metadata(struct dm_snapshot *s)
+static int set_chunk_size(struct dm_snapshot *s, const char *chunk_size_arg,
+			  char **error)
 {
-	if (s->store.read_metadata(&s->store)) {
-		down_write(&s->lock);
-		s->valid = 0;
-		up_write(&s->lock);
+	unsigned long chunk_size;
+	char *value;
+
+	chunk_size = simple_strtoul(chunk_size_arg, &value, 10);
+	if (*chunk_size_arg == '\0' || *value != '\0') {
+		*error = "Invalid chunk size";
+		return -EINVAL;
+	}
+
+	if (!chunk_size) {
+		s->chunk_size = s->chunk_mask = s->chunk_shift = 0;
+		return 0;
+	}
+
+	/*
+	 * Chunk size must be multiple of page size.  Silently
+	 * round up if it's not.
+	 */
+	chunk_size = round_up(chunk_size, PAGE_SIZE >> 9);
+
+	/* Check chunk_size is a power of 2 */
+	if (chunk_size & (chunk_size - 1)) {
+		*error = "Chunk size is not a power of 2";
+		return -EINVAL;
 	}
+
+	/* Validate the chunk size against the device block size */
+	if (chunk_size % (bdev_hardsect_size(s->cow->bdev) >> 9)) {
+		*error = "Chunk size is not a multiple of device blocksize";
+		return -EINVAL;
+	}
+
+	s->chunk_size = chunk_size;
+	s->chunk_mask = chunk_size - 1;
+	s->chunk_shift = ffs(chunk_size) - 1;
+
+	return 0;
 }
 
 /*
@@ -386,16 +438,13 @@ static void read_snapshot_metadata(struct dm_snapshot *s)
 static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 {
 	struct dm_snapshot *s;
-	unsigned long chunk_size;
 	int r = -EINVAL;
 	char persistent;
 	char *origin_path;
 	char *cow_path;
-	char *value;
-	int blocksize;
 
-	if (argc < 4) {
-		ti->error = "dm-snapshot: requires exactly 4 arguments";
+	if (argc != 4) {
+		ti->error = "requires exactly 4 arguments";
 		r = -EINVAL;
 		goto bad1;
 	}
@@ -410,13 +459,6 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 		goto bad1;
 	}
 
-	chunk_size = simple_strtoul(argv[3], &value, 10);
-	if (chunk_size == 0 || value == NULL) {
-		ti->error = "Invalid chunk size";
-		r = -EINVAL;
-		goto bad1;
-	}
-
 	s = kmalloc(sizeof(*s), GFP_KERNEL);
 	if (s == NULL) {
 		ti->error = "Cannot allocate snapshot context private "
@@ -439,36 +481,17 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 		goto bad2;
 	}
 
-	/*
-	 * Chunk size must be multiple of page size.  Silently
-	 * round up if it's not.
-	 */
-	chunk_size = round_up(chunk_size, PAGE_SIZE >> 9);
-
-	/* Validate the chunk size against the device block size */
-	blocksize = s->cow->bdev->bd_disk->queue->hardsect_size;
-	if (chunk_size % (blocksize >> 9)) {
-		ti->error = "Chunk size is not a multiple of device blocksize";
-		r = -EINVAL;
-		goto bad3;
-	}
-
-	/* Check chunk_size is a power of 2 */
-	if (chunk_size & (chunk_size - 1)) {
-		ti->error = "Chunk size is not a power of 2";
-		r = -EINVAL;
+	r = set_chunk_size(s, argv[3], &ti->error);
+	if (r)
 		goto bad3;
-	}
 
-	s->chunk_size = chunk_size;
-	s->chunk_mask = chunk_size - 1;
 	s->type = persistent;
-	s->chunk_shift = ffs(chunk_size) - 1;
 
 	s->valid = 1;
 	s->active = 0;
 	s->last_percent = 0;
 	init_rwsem(&s->lock);
+	spin_lock_init(&s->pe_lock);
 	s->table = ti->table;
 
 	/* Allocate hash table for COW data */
@@ -478,16 +501,12 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 		goto bad3;
 	}
 
-	/*
-	 * Check the persistent flag - done here because we need the iobuf
-	 * to check the LV header
-	 */
 	s->store.snap = s;
 
 	if (persistent == 'P')
-		r = dm_create_persistent(&s->store, chunk_size);
+		r = dm_create_persistent(&s->store);
 	else
-		r = dm_create_transient(&s->store, s, blocksize);
+		r = dm_create_transient(&s->store);
 
 	if (r) {
 		ti->error = "Couldn't create exception store";
@@ -502,7 +521,14 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 	}
 
 	/* Metadata must only be loaded into one table at once */
-	read_snapshot_metadata(s);
+	r = s->store.read_metadata(&s->store);
+	if (r) {
+		ti->error = "Failed to read snapshot metadata";
+		goto bad6;
+	}
+
+	bio_list_init(&s->queued_bios);
+	INIT_WORK(&s->queued_bios_work, flush_queued_bios);
 
 	/* Add snapshot to the list of snapshots for this origin */
 	/* Exceptions aren't triggered till snapshot_resume() is called */
@@ -538,21 +564,28 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 	return r;
 }
 
+static void __free_exceptions(struct dm_snapshot *s)
+{
+	kcopyd_client_destroy(s->kcopyd_client);
+	s->kcopyd_client = NULL;
+
+	exit_exception_table(&s->pending, pending_cache);
+	exit_exception_table(&s->complete, exception_cache);
+
+	s->store.destroy(&s->store);
+}
+
 static void snapshot_dtr(struct dm_target *ti)
 {
 	struct dm_snapshot *s = (struct dm_snapshot *) ti->private;
 
+	flush_workqueue(ksnapd);
+
 	/* Prevent further origin writes from using this snapshot. */
 	/* After this returns there can be no new kcopyd jobs. */
 	unregister_snapshot(s);
 
-	kcopyd_client_destroy(s->kcopyd_client);
-
-	exit_exception_table(&s->pending, pending_cache);
-	exit_exception_table(&s->complete, exception_cache);
-
-	/* Deallocate memory used */
-	s->store.destroy(&s->store);
+	__free_exceptions(s);
 
 	dm_put_device(ti, s->origin);
 	dm_put_device(ti, s->cow);
@@ -575,6 +608,20 @@ static void flush_bios(struct bio *bio)
 	}
 }
 
+static void flush_queued_bios(struct work_struct *work)
+{
+	struct dm_snapshot *s =
+		container_of(work, struct dm_snapshot, queued_bios_work);
+	struct bio *queued_bios;
+	unsigned long flags;
+
+	spin_lock_irqsave(&s->pe_lock, flags);
+	queued_bios = bio_list_get(&s->queued_bios);
+	spin_unlock_irqrestore(&s->pe_lock, flags);
+
+	flush_bios(queued_bios);
+}
+
 /*
  * Error a list of buffers.
  */
@@ -590,81 +637,113 @@ static void error_bios(struct bio *bio)
 	}
 }
 
-static struct bio *__flush_bios(struct pending_exception *pe)
+static void __invalidate_snapshot(struct dm_snapshot *s, int err)
 {
-	struct pending_exception *sibling;
+	if (!s->valid)
+		return;
 
-	if (list_empty(&pe->siblings))
-		return bio_list_get(&pe->origin_bios);
+	if (err == -EIO)
+		DMERR("Invalidating snapshot: Error reading/writing.");
+	else if (err == -ENOMEM)
+		DMERR("Invalidating snapshot: Unable to allocate exception.");
 
-	sibling = list_entry(pe->siblings.next,
-			     struct pending_exception, siblings);
+	if (s->store.drop_snapshot)
+		s->store.drop_snapshot(&s->store);
 
-	list_del(&pe->siblings);
+	s->valid = 0;
 
-	/* This is fine as long as kcopyd is single-threaded. If kcopyd
-	 * becomes multi-threaded, we'll need some locking here.
+	dm_table_event(s->table);
+}
+
+static void get_pending_exception(struct pending_exception *pe)
+{
+	atomic_inc(&pe->ref_count);
+}
+
+static struct bio *put_pending_exception(struct pending_exception *pe)
+{
+	struct pending_exception *primary_pe;
+	struct bio *origin_bios = NULL;
+
+	primary_pe = pe->primary_pe;
+
+	/*
+	 * If this pe is involved in a write to the origin and
+	 * it is the last sibling to complete then release
+	 * the bios for the original write to the origin.
 	 */
-	bio_list_merge(&sibling->origin_bios, &pe->origin_bios);
+	if (primary_pe &&
+	    atomic_dec_and_test(&primary_pe->ref_count))
+		origin_bios = bio_list_get(&primary_pe->origin_bios);
 
-	return NULL;
+	/*
+	 * Free the pe if it's not linked to an origin write or if
+	 * it's not itself a primary pe.
+	 */
+	if (!primary_pe || primary_pe != pe)
+		free_pending_exception(pe);
+
+	/*
+	 * Free the primary pe if nothing references it.
+	 */
+	if (primary_pe && !atomic_read(&primary_pe->ref_count))
+		free_pending_exception(primary_pe);
+
+	return origin_bios;
 }
 
 static void pending_complete(struct pending_exception *pe, int success)
 {
 	struct exception *e;
 	struct dm_snapshot *s = pe->snap;
-	struct bio *flush = NULL;
-
-	if (success) {
-		e = alloc_exception();
-		if (!e) {
-			DMWARN("Unable to allocate exception.");
-			down_write(&s->lock);
-			s->store.drop_snapshot(&s->store);
-			s->valid = 0;
-			flush = __flush_bios(pe);
-			up_write(&s->lock);
-
-			error_bios(bio_list_get(&pe->snapshot_bios));
-			goto out;
-		}
-		*e = pe->e;
-
-		/*
-		 * Add a proper exception, and remove the
-		 * in-flight exception from the list.
-		 */
-		down_write(&s->lock);
-		insert_exception(&s->complete, e);
-		remove_exception(&pe->e);
-		flush = __flush_bios(pe);
-
-		/* Submit any pending write bios */
-		up_write(&s->lock);
+	struct bio *origin_bios = NULL;
+	struct bio *snapshot_bios = NULL;
+	int error = 0;
 
-		flush_bios(bio_list_get(&pe->snapshot_bios));
-	} else {
+	if (!success) {
 		/* Read/write error - snapshot is unusable */
 		down_write(&s->lock);
-		if (s->valid)
-			DMERR("Error reading/writing snapshot");
-		s->store.drop_snapshot(&s->store);
-		s->valid = 0;
-		remove_exception(&pe->e);
-		flush = __flush_bios(pe);
-		up_write(&s->lock);
+		__invalidate_snapshot(s, -EIO);
+		error = 1;
+		goto out;
+	}
 
-		error_bios(bio_list_get(&pe->snapshot_bios));
+	e = alloc_exception();
+	if (!e) {
+		down_write(&s->lock);
+		__invalidate_snapshot(s, -ENOMEM);
+		error = 1;
+		goto out;
+	}
+	*e = pe->e;
 
-		dm_table_event(s->table);
+	down_write(&s->lock);
+	if (!s->valid) {
+		free_exception(e);
+		error = 1;
+		goto out;
 	}
 
+	/*
+	 * Add a proper exception, and remove the
+	 * in-flight exception from the list.
+	 */
+	insert_exception(&s->complete, e);
+
  out:
-	free_pending_exception(pe);
+	remove_exception(&pe->e);
+	snapshot_bios = bio_list_get(&pe->snapshot_bios);
+	origin_bios = put_pending_exception(pe);
 
-	if (flush)
-		flush_bios(flush);
+	up_write(&s->lock);
+
+	/* Submit any pending write bios */
+	if (error)
+		error_bios(snapshot_bios);
+	else
+		flush_bios(snapshot_bios);
+
+	flush_bios(origin_bios);
 }
 
 static void commit_callback(void *context, int success)
@@ -738,38 +817,46 @@ __find_pending_exception(struct dm_snapshot *s, struct bio *bio)
 	if (e) {
 		/* cast the exception to a pending exception */
 		pe = container_of(e, struct pending_exception, e);
+		goto out;
+	}
 
-	} else {
-		/*
-		 * Create a new pending exception, we don't want
-		 * to hold the lock while we do this.
-		 */
-		up_write(&s->lock);
-		pe = alloc_pending_exception();
-		down_write(&s->lock);
+	/*
+	 * Create a new pending exception, we don't want
+	 * to hold the lock while we do this.
+	 */
+	up_write(&s->lock);
+	pe = alloc_pending_exception();
+	down_write(&s->lock);
 
-		e = lookup_exception(&s->pending, chunk);
-		if (e) {
-			free_pending_exception(pe);
-			pe = container_of(e, struct pending_exception, e);
-		} else {
-			pe->e.old_chunk = chunk;
-			bio_list_init(&pe->origin_bios);
-			bio_list_init(&pe->snapshot_bios);
-			INIT_LIST_HEAD(&pe->siblings);
-			pe->snap = s;
-			pe->started = 0;
-
-			if (s->store.prepare_exception(&s->store, &pe->e)) {
-				free_pending_exception(pe);
-				s->valid = 0;
-				return NULL;
-			}
+	if (!s->valid) {
+		free_pending_exception(pe);
+		return NULL;
+	}
 
-			insert_exception(&s->pending, &pe->e);
-		}
+	e = lookup_exception(&s->pending, chunk);
+	if (e) {
+		free_pending_exception(pe);
+		pe = container_of(e, struct pending_exception, e);
+		goto out;
+	}
+
+	pe->e.old_chunk = chunk;
+	bio_list_init(&pe->origin_bios);
+	bio_list_init(&pe->snapshot_bios);
+	pe->primary_pe = NULL;
+	atomic_set(&pe->ref_count, 0);
+	pe->snap = s;
+	pe->started = 0;
+
+	if (s->store.prepare_exception(&s->store, &pe->e)) {
+		free_pending_exception(pe);
+		return NULL;
 	}
 
+	get_pending_exception(pe);
+	insert_exception(&s->pending, &pe->e);
+
+ out:
 	return pe;
 }
 
@@ -786,81 +873,73 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio,
 {
 	struct exception *e;
 	struct dm_snapshot *s = (struct dm_snapshot *) ti->private;
-	int r = 1;
+	int r = DM_MAPIO_REMAPPED;
 	chunk_t chunk;
-	struct pending_exception *pe;
+	struct pending_exception *pe = NULL;
 
 	chunk = sector_to_chunk(s, bio->bi_sector);
 
 	/* Full snapshots are not usable */
+	/* To get here the table must be live so s->active is always set. */
 	if (!s->valid)
 		return -EIO;
 
 	if (unlikely(bio_barrier(bio)))
 		return -EOPNOTSUPP;
 
+	/* FIXME: should only take write lock if we need
+	 * to copy an exception */
+	down_write(&s->lock);
+
+	if (!s->valid) {
+		r = -EIO;
+		goto out_unlock;
+	}
+
+	/* If the block is already remapped - use that, else remap it */
+	e = lookup_exception(&s->complete, chunk);
+	if (e) {
+		remap_exception(s, e, bio);
+		goto out_unlock;
+	}
+
 	/*
 	 * Write to snapshot - higher level takes care of RW/RO
 	 * flags so we should only get this if we are
 	 * writeable.
 	 */
 	if (bio_rw(bio) == WRITE) {
+		pe = __find_pending_exception(s, bio);
+		if (!pe) {
+			__invalidate_snapshot(s, -ENOMEM);
+			r = -EIO;
+			goto out_unlock;
+		}
 
-		/* FIXME: should only take write lock if we need
-		 * to copy an exception */
-		down_write(&s->lock);
+		remap_exception(s, &pe->e, bio);
+		bio_list_add(&pe->snapshot_bios, bio);
 
-		/* If the block is already remapped - use that, else remap it */
-		e = lookup_exception(&s->complete, chunk);
-		if (e) {
-			remap_exception(s, e, bio);
-			up_write(&s->lock);
+		r = DM_MAPIO_SUBMITTED;
 
-		} else {
-			pe = __find_pending_exception(s, bio);
-
-			if (!pe) {
-				if (s->store.drop_snapshot)
-					s->store.drop_snapshot(&s->store);
-				s->valid = 0;
-				r = -EIO;
-				up_write(&s->lock);
-			} else {
-				remap_exception(s, &pe->e, bio);
-				bio_list_add(&pe->snapshot_bios, bio);
-
-				if (!pe->started) {
-					/* this is protected by snap->lock */
-					pe->started = 1;
-					up_write(&s->lock);
-					start_copy(pe);
-				} else
-					up_write(&s->lock);
-				r = 0;
-			}
+		if (!pe->started) {
+			/* this is protected by snap->lock */
+			pe->started = 1;
+			up_write(&s->lock);
+			start_copy(pe);
+			goto out;
 		}
-
-	} else {
+	} else
 		/*
 		 * FIXME: this read path scares me because we
 		 * always use the origin when we have a pending
 		 * exception.  However I can't think of a
 		 * situation where this is wrong - ejt.
 		 */
+		bio->bi_bdev = s->origin->bdev;
 
-		/* Do reads */
-		down_read(&s->lock);
-
-		/* See if it it has been remapped */
-		e = lookup_exception(&s->complete, chunk);
-		if (e)
-			remap_exception(s, e, bio);
-		else
-			bio->bi_bdev = s->origin->bdev;
-
-		up_read(&s->lock);
-	}
-
+ out_unlock:
+	up_write(&s->lock);
+ out:
 	return r;
 }
 
@@ -888,9 +967,9 @@ static int snapshot_status(struct dm_target *ti, status_type_t type,
 				snap->store.fraction_full(&snap->store,
 							  &numerator,
 							  &denominator);
-				snprintf(result, maxlen,
-					 SECTOR_FORMAT "/" SECTOR_FORMAT,
-					 numerator, denominator);
+				snprintf(result, maxlen, "%llu/%llu",
+					(unsigned long long)numerator,
+					(unsigned long long)denominator);
 			}
 			else
 				snprintf(result, maxlen, "Unknown");
@@ -903,9 +982,10 @@ static int snapshot_status(struct dm_target *ti, status_type_t type,
 		 * to make private copies if the output is to
 		 * make sense.
 		 */
-		snprintf(result, maxlen, "%s %s %c " SECTOR_FORMAT,
+		snprintf(result, maxlen, "%s %s %c %llu",
 			 snap->origin->name, snap->cow->name,
-			 snap->type, snap->chunk_size);
+			 snap->type,
+			 (unsigned long long)snap->chunk_size);
 		break;
 	}
 
@@ -915,40 +995,27 @@ static int snapshot_status(struct dm_target *ti, status_type_t type,
 /*-----------------------------------------------------------------
  * Origin methods
  *---------------------------------------------------------------*/
-static void list_merge(struct list_head *l1, struct list_head *l2)
-{
-	struct list_head *l1_n, *l2_p;
-
-	l1_n = l1->next;
-	l2_p = l2->prev;
-
-	l1->next = l2;
-	l2->prev = l1;
-
-	l2_p->next = l1_n;
-	l1_n->prev = l2_p;
-}
-
 static int __origin_write(struct list_head *snapshots, struct bio *bio)
 {
-	int r = 1, first = 1;
+	int r = DM_MAPIO_REMAPPED, first = 0;
 	struct dm_snapshot *snap;
 	struct exception *e;
-	struct pending_exception *pe, *last = NULL;
+	struct pending_exception *pe, *next_pe, *primary_pe = NULL;
 	chunk_t chunk;
+	LIST_HEAD(pe_queue);
 
 	/* Do all the snapshots on this origin */
 	list_for_each_entry (snap, snapshots, list) {
 
+		down_write(&snap->lock);
+
 		/* Only deal with valid and active snapshots */
 		if (!snap->valid || !snap->active)
-			continue;
+			goto next_snapshot;
 
 		/* Nothing to do if writing beyond end of snapshot */
 		if (bio->bi_sector >= dm_table_get_size(snap->table))
-			continue;
-
-		down_write(&snap->lock);
+			goto next_snapshot;
 
 		/*
 		 * Remember, different snapshots can have
@@ -960,49 +1027,74 @@ static int __origin_write(struct list_head *snapshots, struct bio *bio)
 		 * Check exception table to see if block
 		 * is already remapped in this snapshot
 		 * and trigger an exception if not.
+		 *
+		 * ref_count is initialised to 1 so pending_complete()
+		 * won't destroy the primary_pe while we're inside this loop.
 		 */
 		e = lookup_exception(&snap->complete, chunk);
-		if (!e) {
-			pe = __find_pending_exception(snap, bio);
-			if (!pe) {
-				snap->store.drop_snapshot(&snap->store);
-				snap->valid = 0;
-
-			} else {
-				if (last)
-					list_merge(&pe->siblings,
-						   &last->siblings);
-
-				last = pe;
-				r = 0;
+		if (e)
+			goto next_snapshot;
+
+		pe = __find_pending_exception(snap, bio);
+		if (!pe) {
+			__invalidate_snapshot(snap, -ENOMEM);
+			goto next_snapshot;
+		}
+
+		if (!primary_pe) {
+			/*
+			 * Either every pe here has same
+			 * primary_pe or none has one yet.
+			 */
+			if (pe->primary_pe)
+				primary_pe = pe->primary_pe;
+			else {
+				primary_pe = pe;
+				first = 1;
 			}
+
+			bio_list_add(&primary_pe->origin_bios, bio);
+
+			r = DM_MAPIO_SUBMITTED;
 		}
 
+		if (!pe->primary_pe) {
+			pe->primary_pe = primary_pe;
+			get_pending_exception(primary_pe);
+		}
+
+		if (!pe->started) {
+			pe->started = 1;
+			list_add_tail(&pe->list, &pe_queue);
+		}
+
+ next_snapshot:
 		up_write(&snap->lock);
 	}
 
+	if (!primary_pe)
+		return r;
+
 	/*
-	 * Now that we have a complete pe list we can start the copying.
+	 * If this is the first time we're processing this chunk and
+	 * ref_count is now 1 it means all the pending exceptions
+	 * got completed while we were in the loop above, so it falls to
+	 * us here to remove the primary_pe and submit any origin_bios.
 	 */
-	if (last) {
-		pe = last;
-		do {
-			down_write(&pe->snap->lock);
-			if (first)
-				bio_list_add(&pe->origin_bios, bio);
-			if (!pe->started) {
-				pe->started = 1;
-				up_write(&pe->snap->lock);
-				start_copy(pe);
-			} else
-				up_write(&pe->snap->lock);
-			first = 0;
-			pe = list_entry(pe->siblings.next,
-					struct pending_exception, siblings);
-
-		} while (pe != last);
+
+	if (first && atomic_dec_and_test(&primary_pe->ref_count)) {
+		flush_bios(bio_list_get(&primary_pe->origin_bios));
+		free_pending_exception(primary_pe);
+		/* If we got here, pe_queue is necessarily empty. */
+		return r;
 	}
 
+	/*
+	 * Now that we have a complete pe list we can start the copying.
+	 */
+	list_for_each_entry_safe(pe, next_pe, &pe_queue, list)
+		start_copy(pe);
+
 	return r;
 }
 
@@ -1012,7 +1104,7 @@ static int __origin_write(struct list_head *snapshots, struct bio *bio)
 static int do_origin(struct dm_dev *origin, struct bio *bio)
 {
 	struct origin *o;
-	int r = 1;
+	int r = DM_MAPIO_REMAPPED;
 
 	down_read(&_origins_lock);
 	o = __lookup_origin(origin->bdev);
@@ -1038,7 +1130,7 @@ static int origin_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 	struct dm_dev *dev;
 
 	if (argc != 1) {
-		ti->error = "dm-origin: incorrect number of arguments";
+		ti->error = "origin: incorrect number of arguments";
 		return -EINVAL;
 	}
 
@@ -1069,7 +1161,7 @@ static int origin_map(struct dm_target *ti, struct bio *bio,
 		return -EOPNOTSUPP;
 
 	/* Only tell snapshots if this is a write */
-	return (bio_rw(bio) == WRITE) ? do_origin(dev, bio) : 1;
+	return (bio_rw(bio) == WRITE) ? do_origin(dev, bio) : DM_MAPIO_REMAPPED;
 }
 
 #define min_not_zero(l, r) (l == 0) ? r : ((r == 0) ? l : min(l, r))
@@ -1115,7 +1207,7 @@ static int origin_status(struct dm_target *ti, status_type_t type, char *result,
 
 static struct target_type origin_target = {
 	.name    = "snapshot-origin",
-	.version = {1, 4, 0},
+	.version = {1, 5, 0},
 	.module  = THIS_MODULE,
 	.ctr     = origin_ctr,
 	.dtr     = origin_dtr,
@@ -1126,7 +1218,7 @@ static struct target_type origin_target = {
 
 static struct target_type snapshot_target = {
 	.name    = "snapshot",
-	.version = {1, 4, 0},
+	.version = {1, 5, 0},
 	.module  = THIS_MODULE,
 	.ctr     = snapshot_ctr,
 	.dtr     = snapshot_dtr,
@@ -1147,7 +1239,7 @@ static int __init dm_snapshot_init(void)
 
 	r = dm_register_target(&origin_target);
 	if (r < 0) {
-		DMERR("Device mapper: Origin: register failed %d\n", r);
+		DMERR("Origin target register failed %d", r);
 		goto bad1;
 	}
 
@@ -1178,16 +1270,24 @@ static int __init dm_snapshot_init(void)
 		goto bad4;
 	}
 
-	pending_pool = mempool_create(128, mempool_alloc_slab,
-				      mempool_free_slab, pending_cache);
+	pending_pool = mempool_create_slab_pool(128, pending_cache);
 	if (!pending_pool) {
 		DMERR("Couldn't create pending pool.");
 		r = -ENOMEM;
 		goto bad5;
 	}
 
+	ksnapd = create_singlethread_workqueue("ksnapd");
+	if (!ksnapd) {
+		DMERR("Failed to create ksnapd workqueue.");
+		r = -ENOMEM;
+		goto bad6;
+	}
+
 	return 0;
 
+      bad6:
+	mempool_destroy(pending_pool);
       bad5:
 	kmem_cache_destroy(pending_cache);
       bad4:
@@ -1205,6 +1305,8 @@ static void __exit dm_snapshot_exit(void)
 {
 	int r;
 
+	destroy_workqueue(ksnapd);
+
 	r = dm_unregister_target(&snapshot_target);
 	if (r)
 		DMERR("snapshot unregister failed %d", r);