diff options
Diffstat (limited to 'fs/bcachefs/btree_trans_commit.c')
| -rw-r--r-- | fs/bcachefs/btree_trans_commit.c | 37 |
1 files changed, 37 insertions, 0 deletions
diff --git a/fs/bcachefs/btree_trans_commit.c b/fs/bcachefs/btree_trans_commit.c index a2579d637197..9b6f19ded5cf 100644 --- a/fs/bcachefs/btree_trans_commit.c +++ b/fs/bcachefs/btree_trans_commit.c @@ -459,6 +459,43 @@ static int btree_key_can_insert_cached(struct btree_trans *trans, unsigned flags /* Triggers: */ +/* + * Trigger ordering has some subtleties: + * + * Extent triggers will add a reference to an alloc key (for a bucket) on + * insert, and delete that reference when the extent is removed. + * + * When the last reference to a bucket or indirect extent is deleted, the bucket + * will transition states to need_discard or the indirect extent will be + * deleted. This means that when an extent is being moved (by e.g. the + * finsert/fcollapse paths, or by the reflink code turning an extent into an + * indirect extent), if we process the trigger for the delete before the trigger + * for the insert Bad Things (tm) will happen. + * + * To avoid this, we always run triggers for inserts before triggers for + * overwrites. + * + * There's a complication: various triggers need to see both the old and the new + * key at the same time, if they're keys that have the same trigger - this + * breaks our strict insert-before-overwrite ordering, but not in a way that + * breaks moving extents (XXX: why?) + * + * Additionally, we run alloc triggers last - XXX, also why? + * + * Another, related trigger ordering issue not handled here: backpointers (as + * well as LRU entries) are inserted/removed by triggers that do simple + * inserts/updates - i.e. they don't increment/decrement usage counts, like + * alloc key/reflink btree updates. + * + * This means they have to run in the reverse order, overwrites before inserts: + * but the backpointers and LRU btrees do not themselves have triggers so the + * delete-then-recreate issue for alloc btree references does not happen here. + * + * To get the correct ordering for LRU/backpointer updates, we explicitly put + * the update on either the head or the tail of the list of pending updates, if + * it was an overwrite or an insert, respectively. + */ + static int run_one_mem_trigger(struct btree_trans *trans, struct btree_insert_entry *i, unsigned flags) |