btrfs: log messages at unpin_extent_range() during unexpected cases

At unpin_extent_range() we trigger a WARN_ON() when we don't find an
extent map or we find one with a start offset not matching the start
offset of the target range. This however isn't very useful for debugging
because:

1) We don't know which condition was triggered, as they are both in the
   same WARN_ON() call;

2) We don't know which inode was affected, from which root, for which
   range, what's the start offset of the extent map, and so on.

So trigger a separate warning for each case and log a message for each
case providing information about the inode, its root, the target range,
the generation and the start offset of the extent map we found.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_map.c

@@ -280,7 +280,7 @@ static void try_merge_map(struct extent_map_tree *tree, struct extent_map *em)
 /*
  * Unpin an extent from the cache.
  *
- * @tree:	tree to unpin the extent in
+ * @inode:	the inode from which we are unpinning an extent range
  * @start:	logical offset in the file
  * @len:	length of the extent
  * @gen:	generation that this extent has been modified in
@@ -289,9 +289,10 @@ static void try_merge_map(struct extent_map_tree *tree, struct extent_map *em)
  * to the generation that actually added the file item to the inode so we know
  * we need to sync this extent when we call fsync().
  */
-int unpin_extent_cache(struct extent_map_tree *tree, u64 start, u64 len,
-		       u64 gen)
+int unpin_extent_cache(struct btrfs_inode *inode, u64 start, u64 len, u64 gen)
 {
+	struct btrfs_fs_info *fs_info = inode->root->fs_info;
+	struct extent_map_tree *tree = &inode->extent_tree;
 	int ret = 0;
 	struct extent_map *em;
 	bool prealloc = false;
@@ -299,10 +300,19 @@ int unpin_extent_cache(struct extent_map_tree *tree, u64 start, u64 len,
 	write_lock(&tree->lock);
 	em = lookup_extent_mapping(tree, start, len);
 
-	WARN_ON(!em || em->start != start);
-
-	if (!em)
+	if (WARN_ON(!em)) {
+		btrfs_warn(fs_info,
+"no extent map found for inode %llu (root %lld) when unpinning extent range [%llu, %llu), generation %llu",
+			   btrfs_ino(inode), btrfs_root_id(inode->root),
+			   start, len, gen);
 		goto out;
+	}
+
+	if (WARN_ON(em->start != start))
+		btrfs_warn(fs_info,
+"found extent map for inode %llu (root %lld) with unexpected start offset %llu when unpinning extent range [%llu, %llu), generation %llu",
+			   btrfs_ino(inode), btrfs_root_id(inode->root),
+			   em->start, start, len, gen);
 
 	em->generation = gen;
 	clear_bit(EXTENT_FLAG_PINNED, &em->flags);

fs/btrfs/extent_map.h

@@ -82,7 +82,7 @@ struct extent_map *alloc_extent_map(void);
 void free_extent_map(struct extent_map *em);
 int __init extent_map_init(void);
 void __cold extent_map_exit(void);
-int unpin_extent_cache(struct extent_map_tree *tree, u64 start, u64 len, u64 gen);
+int unpin_extent_cache(struct btrfs_inode *inode, u64 start, u64 len, u64 gen);
 void clear_em_logging(struct extent_map_tree *tree, struct extent_map *em);
 struct extent_map *search_extent_mapping(struct extent_map_tree *tree,
 					 u64 start, u64 len);

fs/btrfs/inode.c

@@ -3127,7 +3127,7 @@ int btrfs_finish_one_ordered(struct btrfs_ordered_extent *ordered_extent)
 						ordered_extent->disk_num_bytes);
 		}
 	}
-	unpin_extent_cache(&inode->extent_tree, ordered_extent->file_offset,
+	unpin_extent_cache(inode, ordered_extent->file_offset,
 			   ordered_extent->num_bytes, trans->transid);
 	if (ret < 0) {
 		btrfs_abort_transaction(trans, ret);