dm thin metadata: fix bug in dm_thin_remove_range()

dm_btree_remove_leaves() only unmaps a contiguous region so we need a
loop, in __remove_range(), to handle ranges that contain multiple
regions.

A new btree function, dm_btree_lookup_next(), is introduced which is
more efficiently able to skip over regions of the thin device which
aren't mapped.  __remove_range() uses dm_btree_lookup_next() for each
iteration of __remove_range()'s loop.

Also, improve description of dm_btree_remove_leaves().

Fixes: 6550f075 ("dm thin metadata: add dm_thin_remove_range()")
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org # 4.1+

drivers/md/dm-thin-metadata.c

@@ -1538,7 +1538,7 @@ static int __remove(struct dm_thin_device *td, dm_block_t block)
 static int __remove_range(struct dm_thin_device *td, dm_block_t begin, dm_block_t end)
 {
 	int r;
-	unsigned count;
+	unsigned count, total_count = 0;
 	struct dm_pool_metadata *pmd = td->pmd;
 	dm_block_t keys[1] = { td->id };
 	__le64 value;
@@ -1561,11 +1561,29 @@ static int __remove_range(struct dm_thin_device *td, dm_block_t begin, dm_block_
 	if (r)
 		return r;
 
+	/*
+	 * Remove leaves stops at the first unmapped entry, so we have to
+	 * loop round finding mapped ranges.
+	 */
+	while (begin < end) {
+		r = dm_btree_lookup_next(&pmd->bl_info, mapping_root, &begin, &begin, &value);
+		if (r == -ENODATA)
+			break;
+
+		if (r)
+			return r;
+
+		if (begin >= end)
+			break;
+
 		r = dm_btree_remove_leaves(&pmd->bl_info, mapping_root, &begin, end, &mapping_root, &count);
 		if (r)
 			return r;
 
-	td->mapped_blocks -= count;
+		total_count += count;
+	}
+
+	td->mapped_blocks -= total_count;
 	td->changed = 1;
 
 	/*

drivers/md/persistent-data/dm-btree.c

@@ -63,6 +63,11 @@ int lower_bound(struct btree_node *n, uint64_t key)
 	return bsearch(n, key, 0);
 }
 
+static int upper_bound(struct btree_node *n, uint64_t key)
+{
+	return bsearch(n, key, 1);
+}
+
 void inc_children(struct dm_transaction_manager *tm, struct btree_node *n,
 		  struct dm_btree_value_type *vt)
 {
@@ -392,6 +397,82 @@ int dm_btree_lookup(struct dm_btree_info *info, dm_block_t root,
 }
 EXPORT_SYMBOL_GPL(dm_btree_lookup);
 
+static int dm_btree_lookup_next_single(struct dm_btree_info *info, dm_block_t root,
+				       uint64_t key, uint64_t *rkey, void *value_le)
+{
+	int r, i;
+	uint32_t flags, nr_entries;
+	struct dm_block *node;
+	struct btree_node *n;
+
+	r = bn_read_lock(info, root, &node);
+	if (r)
+		return r;
+
+	n = dm_block_data(node);
+	flags = le32_to_cpu(n->header.flags);
+	nr_entries = le32_to_cpu(n->header.nr_entries);
+
+	if (flags & INTERNAL_NODE) {
+		i = lower_bound(n, key);
+		if (i < 0 || i >= nr_entries) {
+			r = -ENODATA;
+			goto out;
+		}
+
+		r = dm_btree_lookup_next_single(info, value64(n, i), key, rkey, value_le);
+		if (r == -ENODATA && i < (nr_entries - 1)) {
+			i++;
+			r = dm_btree_lookup_next_single(info, value64(n, i), key, rkey, value_le);
+		}
+
+	} else {
+		i = upper_bound(n, key);
+		if (i < 0 || i >= nr_entries) {
+			r = -ENODATA;
+			goto out;
+		}
+
+		*rkey = le64_to_cpu(n->keys[i]);
+		memcpy(value_le, value_ptr(n, i), info->value_type.size);
+	}
+out:
+	dm_tm_unlock(info->tm, node);
+	return r;
+}
+
+int dm_btree_lookup_next(struct dm_btree_info *info, dm_block_t root,
+			 uint64_t *keys, uint64_t *rkey, void *value_le)
+{
+	unsigned level;
+	int r = -ENODATA;
+	__le64 internal_value_le;
+	struct ro_spine spine;
+
+	init_ro_spine(&spine, info);
+	for (level = 0; level < info->levels - 1u; level++) {
+		r = btree_lookup_raw(&spine, root, keys[level],
+				     lower_bound, rkey,
+				     &internal_value_le, sizeof(uint64_t));
+		if (r)
+			goto out;
+
+		if (*rkey != keys[level]) {
+			r = -ENODATA;
+			goto out;
+		}
+
+		root = le64_to_cpu(internal_value_le);
+	}
+
+	r = dm_btree_lookup_next_single(info, root, keys[level], rkey, value_le);
+out:
+	exit_ro_spine(&spine);
+	return r;
+}
+
+EXPORT_SYMBOL_GPL(dm_btree_lookup_next);
+
 /*
  * Splits a node by creating a sibling node and shifting half the nodes
  * contents across.  Assumes there is a parent node, and it has room for

drivers/md/persistent-data/dm-btree.h

@@ -109,6 +109,13 @@ int dm_btree_del(struct dm_btree_info *info, dm_block_t root);
 int dm_btree_lookup(struct dm_btree_info *info, dm_block_t root,
 		    uint64_t *keys, void *value_le);
 
+/*
+ * Tries to find the first key where the bottom level key is >= to that
+ * given.  Useful for skipping empty sections of the btree.
+ */
+int dm_btree_lookup_next(struct dm_btree_info *info, dm_block_t root,
+			 uint64_t *keys, uint64_t *rkey, void *value_le);
+
 /*
  * Insertion (or overwrite an existing value).  O(ln(n))
  */
@@ -135,9 +142,10 @@ int dm_btree_remove(struct dm_btree_info *info, dm_block_t root,
 		    uint64_t *keys, dm_block_t *new_root);
 
 /*
- * Removes values between 'keys' and keys2, where keys2 is keys with the
- * final key replaced with 'end_key'.  'end_key' is the one-past-the-end
- * value.  'keys' may be altered.
+ * Removes a _contiguous_ run of values starting from 'keys' and not
+ * reaching keys2 (where keys2 is keys with the final key replaced with
+ * 'end_key').  'end_key' is the one-past-the-end value.  'keys' may be
+ * altered.
  */
 int dm_btree_remove_leaves(struct dm_btree_info *info, dm_block_t root,
 			   uint64_t *keys, uint64_t end_key,