btrfs: add tracepoints for ordered extents

When debugging a reference counting issue with ordered extents, I've found
we're lacking a lot of tracepoint coverage in the ordered extent code.

Close these gaps by adding tracepoints after every refcount_inc() in the
ordered extent code.
Reviewed-by: Boris Burkov <boris@bur.io>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ordered-data.c

@@ -401,6 +401,7 @@ void btrfs_mark_ordered_io_finished(struct btrfs_inode *inode,
 			set_bit(BTRFS_ORDERED_IO_DONE, &entry->flags);
 			cond_wake_up(&entry->wait);
 			refcount_inc(&entry->refs);
+			trace_btrfs_ordered_extent_mark_finished(inode, entry);
 			spin_unlock_irqrestore(&tree->lock, flags);
 			btrfs_init_work(&entry->work, finish_func, NULL, NULL);
 			btrfs_queue_work(wq, &entry->work);
@@ -473,6 +474,7 @@ bool btrfs_dec_test_ordered_pending(struct btrfs_inode *inode,
 	if (finished && cached && entry) {
 		*cached = entry;
 		refcount_inc(&entry->refs);
+		trace_btrfs_ordered_extent_dec_test_pending(inode, entry);
 	}
 	spin_unlock_irqrestore(&tree->lock, flags);
 	return finished;
@@ -807,8 +809,10 @@ struct btrfs_ordered_extent *btrfs_lookup_ordered_extent(struct btrfs_inode *ino
 	entry = rb_entry(node, struct btrfs_ordered_extent, rb_node);
 	if (!in_range(file_offset, entry->file_offset, entry->num_bytes))
 		entry = NULL;
-	if (entry)
+	if (entry) {
 		refcount_inc(&entry->refs);
+		trace_btrfs_ordered_extent_lookup(inode, entry);
+	}
 out:
 	spin_unlock_irqrestore(&tree->lock, flags);
 	return entry;
@@ -848,8 +852,10 @@ struct btrfs_ordered_extent *btrfs_lookup_ordered_range(
 			break;
 	}
 out:
-	if (entry)
+	if (entry) {
 		refcount_inc(&entry->refs);
+		trace_btrfs_ordered_extent_lookup_range(inode, entry);
+	}
 	spin_unlock_irq(&tree->lock);
 	return entry;
 }
@@ -878,6 +884,7 @@ void btrfs_get_ordered_extents_for_logging(struct btrfs_inode *inode,
 		ASSERT(list_empty(&ordered->log_list));
 		list_add_tail(&ordered->log_list, list);
 		refcount_inc(&ordered->refs);
+		trace_btrfs_ordered_extent_lookup_for_logging(inode, ordered);
 	}
 	spin_unlock_irq(&tree->lock);
 }
@@ -901,6 +908,7 @@ btrfs_lookup_first_ordered_extent(struct btrfs_inode *inode, u64 file_offset)
 
 	entry = rb_entry(node, struct btrfs_ordered_extent, rb_node);
 	refcount_inc(&entry->refs);
+	trace_btrfs_ordered_extent_lookup_first(inode, entry);
 out:
 	spin_unlock_irq(&tree->lock);
 	return entry;
@@ -975,8 +983,11 @@ struct btrfs_ordered_extent *btrfs_lookup_first_ordered_range(
 	/* No ordered extent in the range */
 	entry = NULL;
 out:
-	if (entry)
+	if (entry) {
 		refcount_inc(&entry->refs);
+		trace_btrfs_ordered_extent_lookup_first_range(inode, entry);
+	}
+
 	spin_unlock_irq(&tree->lock);
 	return entry;
 }
@@ -1055,6 +1066,8 @@ int btrfs_split_ordered_extent(struct btrfs_ordered_extent *ordered, u64 pre,
 	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
 	int ret = 0;
 
+	trace_btrfs_ordered_extent_split(BTRFS_I(inode), ordered);
+
 	spin_lock_irq(&tree->lock);
 	/* Remove from tree once */
 	node = &ordered->rb_node;

include/trace/events/btrfs.h

@@ -598,6 +598,70 @@ DEFINE_EVENT(btrfs__ordered_extent, btrfs_ordered_extent_put,
 	TP_ARGS(inode, ordered)
 );
 
+DEFINE_EVENT(btrfs__ordered_extent, btrfs_ordered_extent_lookup,
+
+	     TP_PROTO(const struct btrfs_inode *inode,
+		      const struct btrfs_ordered_extent *ordered),
+
+	     TP_ARGS(inode, ordered)
+);
+
+DEFINE_EVENT(btrfs__ordered_extent, btrfs_ordered_extent_lookup_range,
+
+	     TP_PROTO(const struct btrfs_inode *inode,
+		      const struct btrfs_ordered_extent *ordered),
+
+	     TP_ARGS(inode, ordered)
+);
+
+DEFINE_EVENT(btrfs__ordered_extent, btrfs_ordered_extent_lookup_first_range,
+
+	     TP_PROTO(const struct btrfs_inode *inode,
+		      const struct btrfs_ordered_extent *ordered),
+
+	     TP_ARGS(inode, ordered)
+);
+
+DEFINE_EVENT(btrfs__ordered_extent, btrfs_ordered_extent_lookup_for_logging,
+
+	     TP_PROTO(const struct btrfs_inode *inode,
+		      const struct btrfs_ordered_extent *ordered),
+
+	     TP_ARGS(inode, ordered)
+);
+
+DEFINE_EVENT(btrfs__ordered_extent, btrfs_ordered_extent_lookup_first,
+
+	     TP_PROTO(const struct btrfs_inode *inode,
+		      const struct btrfs_ordered_extent *ordered),
+
+	     TP_ARGS(inode, ordered)
+);
+
+DEFINE_EVENT(btrfs__ordered_extent, btrfs_ordered_extent_split,
+
+	     TP_PROTO(const struct btrfs_inode *inode,
+		      const struct btrfs_ordered_extent *ordered),
+
+	     TP_ARGS(inode, ordered)
+);
+
+DEFINE_EVENT(btrfs__ordered_extent, btrfs_ordered_extent_dec_test_pending,
+
+	     TP_PROTO(const struct btrfs_inode *inode,
+		      const struct btrfs_ordered_extent *ordered),
+
+	     TP_ARGS(inode, ordered)
+);
+
+DEFINE_EVENT(btrfs__ordered_extent, btrfs_ordered_extent_mark_finished,
+
+	     TP_PROTO(const struct btrfs_inode *inode,
+		      const struct btrfs_ordered_extent *ordered),
+
+	     TP_ARGS(inode, ordered)
+);
+
 DECLARE_EVENT_CLASS(btrfs__writepage,
 
 	TP_PROTO(const struct page *page, const struct inode *inode,