[PATCH] Btrfs: make sure we find a bitmap entry

[Josef Bacik <josef@redhat.com>]

Yan Zheng hit a problem where we tried to remove some free space but failed
because we couldn't find the free space entry.  This is because the free space
was held within a bitmap that had a starting offset well before the actual
offset of the free space, and there were free space extents that were in the
same range as that offset, so tree_search_offset returned with NULL because we
couldn't find a free space extent that had that offset.  This is fixed by making
sure that if we fail to find the entry, we re-search again with bitmap_only set
to 1 and do an offset_to_bitmap so we can get the appropriate bitmap.  A similar
problem happens in btrfs_alloc_from_bitmap for the clustering code, but that is
not as bad since we will just go and redo our cluster allocation.

Also this adds some debugging stuff to make sure that the free space we are
trying to remove from the bitmap is in fact there.  This can probably go away
after a while, but since this code is only used by the tree-logging stuff it
would be nice to run with it for a while to make sure there are no problems.
Thanks,

Signed-off-by: Josef Bacik <jbacik@redhat.com>
---
 fs/btrfs/free-space-cache.c |   40 +++++++++++++++++++++++++++++++---------
 1 files changed, 31 insertions(+), 9 deletions(-)

diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index af99b78..691ea95 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -414,11 +414,20 @@ static noinline int remove_from_bitmap(struct btrfs_block_group_cache *block_gro
 			      u64 *offset, u64 *bytes)
 {
 	u64 end;
+	u64 search_start, search_bytes;
+	int ret;
 
 again:
 	end = bitmap_info->offset +
 		(u64)(BITS_PER_BITMAP * block_group->sectorsize) - 1;
 
+	search_start = *offset;
+	search_bytes = *bytes;
+
+	ret = search_bitmap(block_group, bitmap_info, &search_start,
+			    &search_bytes);
+	BUG_ON(ret < 0 || search_start != *offset);
+
 	if (*offset > bitmap_info->offset && *offset + *bytes > end) {
 		bitmap_clear_bits(block_group, bitmap_info, *offset,
 				  end - *offset + 1);
@@ -430,6 +439,7 @@ again:
 	}
 
 	if (*bytes) {
+		struct rb_node *next = rb_next(&bitmap_info->offset_index);
 		if (!bitmap_info->bytes) {
 			unlink_free_space(block_group, bitmap_info);
 			kfree(bitmap_info->bitmap);
@@ -438,16 +448,22 @@ again:
 			recalculate_thresholds(block_group);
 		}
 
-		bitmap_info = tree_search_offset(block_group,
-						 offset_to_bitmap(block_group,
-								  *offset),
-						 1, 0);
-		if (!bitmap_info)
+		if (!next)
 			return -EINVAL;
 
+		bitmap_info = rb_entry(next, struct btrfs_free_space,
+				       offset_index);
 		if (!bitmap_info->bitmap)
 			return -EAGAIN;
 
+		search_start = *offset;
+		search_bytes = *bytes;
+
+		ret = search_bitmap(block_group, bitmap_info, &search_start,
+				    &search_bytes);
+		if (ret < 0 || search_start != *offset)
+			return -EAGAIN;
+
 		goto again;
 	} else if (!bitmap_info->bytes) {
 		unlink_free_space(block_group, bitmap_info);
@@ -644,8 +660,13 @@ int btrfs_remove_free_space(struct btrfs_block_group_cache *block_group,
 again:
 	info = tree_search_offset(block_group, offset, 0, 0);
 	if (!info) {
-		WARN_ON(1);
-		goto out_lock;
+		info = tree_search_offset(block_group,
+					  offset_to_bitmap(block_group, offset),
+					  1, 0);
+		if (!info) {
+			WARN_ON(1);
+			goto out_lock;
+		}
 	}
 
 	if (info->bytes < bytes && rb_next(&info->offset_index)) {
@@ -957,8 +978,9 @@ static u64 btrfs_alloc_from_bitmap(struct btrfs_block_group_cache *block_group,
 	if (cluster->block_group != block_group)
 		goto out;
 
-	entry = tree_search_offset(block_group, search_start, 0, 0);
-
+	entry = tree_search_offset(block_group,
+				   offset_to_bitmap(block_group, search_start),
+				   1, 0);
 	if (!entry || !entry->bitmap)
 		goto out;
 
-- 
1.5.4.3