bcachefs: Revalidate pointer to old bkey val before calling mem triggers

We recently started stashing a copy of the key being overwritten in
btree_insert_entry: this is helpful for avoiding multiple calls to
bch2_btree_path_peek_slot() and bch2_journal_keys_peek() in the
transaction commit path.

But it turns out this has a problem - when we run mem/atomic triggers,
we've done a couple things that can invalidate the pointer to the old
key's value. This makes the optimization of stashing a pointer to the
old value questionable, but for now this patch revalidates that pointer
before running mem triggers.

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

diff --git a/fs/bcachefs/btree_update_leaf.c b/fs/bcachefs/btree_update_leaf.c
index 9925254c5446ab53dcc64464f9223e61aeef1505..a789a7cf4c744c98fb5149b398682590bfdccff3 100644 (file)
--- a/fs/bcachefs/btree_update_leaf.c
+++ b/fs/bcachefs/btree_update_leaf.c
@@ -660,6 +660,32 @@ bch2_trans_commit_write_locked(struct btree_trans *trans,
 
                if (btree_node_type_needs_gc(i->bkey_type))
                        marking = true;
+
+               /*
+                * Revalidate before calling mem triggers - XXX, ugly:
+                *
+                * - successful btree node splits don't cause transaction
+                *   restarts and will have invalidated the pointer to the bkey
+                *   value
+                * - btree_node_lock_for_insert() -> btree_node_prep_for_write()
+                *   when it has to resort
+                * - btree_key_can_insert_cached() when it has to reallocate
+                *
+                *   Ugly because we currently have no way to tell if the
+                *   pointer's been invalidated, which means it's debatabale
+                *   whether we should be stashing the old key at all.
+                */
+               i->old_v = bch2_btree_path_peek_slot(i->path, &i->old_k).v;
+
+               if (unlikely(!test_bit(JOURNAL_REPLAY_DONE, &c->journal.flags))) {
+                       struct bkey_i *j_k =
+                               bch2_journal_keys_peek(c, i->btree_id, i->level, i->k->k.p);
+
+                       if (j_k && !bpos_cmp(j_k->k.p, i->k->k.p)) {
+                               i->old_k = j_k->k;
+                               i->old_v = &j_k->v;
+                       }
+               }
        }
 
        /*