bcachefs: Journal pins must always have a flush_fn

flush_fn is how we identify journal pins in debugfs - this is a
debugging aid.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_trans_commit.c

@@ -840,6 +840,12 @@ static noinline int bch2_trans_commit_bkey_invalid(struct btree_trans *trans,
 	return -EINVAL;
 }
 
+static int bch2_trans_commit_journal_pin_flush(struct journal *j,
+				struct journal_entry_pin *_pin, u64 seq)
+{
+	return 0;
+}
+
 /*
  * Get journal reservation, take write locks, and attempt to do btree update(s):
  */
@@ -883,7 +889,8 @@ static inline int do_bch2_trans_commit(struct btree_trans *trans, unsigned flags
 
 	if (!ret && trans->journal_pin)
 		bch2_journal_pin_add(&c->journal, trans->journal_res.seq,
-				     trans->journal_pin, NULL);
+				     trans->journal_pin,
+				     bch2_trans_commit_journal_pin_flush);
 
 	/*
 	 * Drop journal reservation after dropping write locks, since dropping

fs/bcachefs/btree_update_interior.c

@@ -815,6 +815,12 @@ static void btree_update_updated_node(struct btree_update *as, struct btree *b)
 	mutex_unlock(&c->btree_interior_update_lock);
 }
 
+static int bch2_update_reparent_journal_pin_flush(struct journal *j,
+				struct journal_entry_pin *_pin, u64 seq)
+{
+	return 0;
+}
+
 static void btree_update_reparent(struct btree_update *as,
 				  struct btree_update *child)
 {
@@ -825,7 +831,8 @@ static void btree_update_reparent(struct btree_update *as,
 	child->b = NULL;
 	child->mode = BTREE_INTERIOR_UPDATING_AS;
 
-	bch2_journal_pin_copy(&c->journal, &as->journal, &child->journal, NULL);
+	bch2_journal_pin_copy(&c->journal, &as->journal, &child->journal,
+			      bch2_update_reparent_journal_pin_flush);
 }
 
 static void btree_update_updated_root(struct btree_update *as, struct btree *b)
@@ -934,6 +941,12 @@ static void bch2_btree_update_get_open_buckets(struct btree_update *as, struct b
 			b->ob.v[--b->ob.nr];
 }
 
+static int bch2_btree_update_will_free_node_journal_pin_flush(struct journal *j,
+				struct journal_entry_pin *_pin, u64 seq)
+{
+	return 0;
+}
+
 /*
  * @b is being split/rewritten: it may have pointers to not-yet-written btree
  * nodes and thus outstanding btree_updates - redirect @b's
@@ -985,11 +998,13 @@ static void bch2_btree_interior_update_will_free_node(struct btree_update *as,
 	 * when the new nodes are persistent and reachable on disk:
 	 */
 	w = btree_current_write(b);
-	bch2_journal_pin_copy(&c->journal, &as->journal, &w->journal, NULL);
+	bch2_journal_pin_copy(&c->journal, &as->journal, &w->journal,
+			      bch2_btree_update_will_free_node_journal_pin_flush);
 	bch2_journal_pin_drop(&c->journal, &w->journal);
 
 	w = btree_prev_write(b);
-	bch2_journal_pin_copy(&c->journal, &as->journal, &w->journal, NULL);
+	bch2_journal_pin_copy(&c->journal, &as->journal, &w->journal,
+			      bch2_btree_update_will_free_node_journal_pin_flush);
 	bch2_journal_pin_drop(&c->journal, &w->journal);
 
 	mutex_unlock(&c->btree_interior_update_lock);

fs/bcachefs/btree_write_buffer.c

@@ -11,6 +11,9 @@
 
 #include <linux/sort.h>
 
+static int bch2_btree_write_buffer_journal_flush(struct journal *,
+				struct journal_entry_pin *, u64);
+
 static int btree_write_buffered_key_cmp(const void *_l, const void *_r)
 {
 	const struct btree_write_buffered_key *l = _l;
@@ -150,7 +153,8 @@ int __bch2_btree_write_buffer_flush(struct btree_trans *trans, unsigned commit_f
 	if (!locked && !mutex_trylock(&wb->flush_lock))
 		return 0;
 
-	bch2_journal_pin_copy(j, &pin, &wb->journal_pin, NULL);
+	bch2_journal_pin_copy(j, &pin, &wb->journal_pin,
+			      bch2_btree_write_buffer_journal_flush);
 	bch2_journal_pin_drop(j, &wb->journal_pin);
 
 	s = btree_write_buffer_switch(wb);
@@ -252,16 +256,8 @@ int __bch2_btree_write_buffer_flush(struct btree_trans *trans, unsigned commit_f
 		if (!i->journal_seq)
 			continue;
 
-		if (i->journal_seq > pin.seq) {
-			struct journal_entry_pin pin2;
-
-			memset(&pin2, 0, sizeof(pin2));
-
-			bch2_journal_pin_add(j, i->journal_seq, &pin2, NULL);
-			bch2_journal_pin_drop(j, &pin);
-			bch2_journal_pin_copy(j, &pin, &pin2, NULL);
-			bch2_journal_pin_drop(j, &pin2);
-		}
+		bch2_journal_pin_update(j, i->journal_seq, &pin,
+			      bch2_btree_write_buffer_journal_flush);
 
 		ret = commit_do(trans, NULL, NULL,
 				commit_flags|

fs/bcachefs/journal_reclaim.c

@@ -374,14 +374,16 @@ static inline void bch2_journal_pin_set_locked(struct journal *j, u64 seq,
 {
 	struct journal_entry_pin_list *pin_list = journal_seq_pin(j, seq);
 
+	/*
+	 * flush_fn is how we identify journal pins in debugfs, so must always
+	 * exist, even if it doesn't do anything:
+	 */
+	BUG_ON(!flush_fn);
+
 	atomic_inc(&pin_list->count);
 	pin->seq	= seq;
 	pin->flush	= flush_fn;
-
-	if (flush_fn)
-		list_add(&pin->list, &pin_list->list[type]);
-	else
-		list_add(&pin->list, &pin_list->flushed);
+	list_add(&pin->list, &pin_list->list[type]);
 }
 
 void bch2_journal_pin_copy(struct journal *j,