bcachefs: Drop unneeded journal pin in bch2_btree_update_start()

When we do an interior btree update, we create new btree nodes and link
them into the btree in memory, but they don't become reachable on disk
until later, when btree_update_nodes_written_trans() runs.

Updates to the new nodes can thus happen before they're reachable on
disk, and if the updates to those new nodes are written before the nodes
become reachable, we would then drop the journal pin for those updates
before the btree has them.

This is what the journal pin in bch2_btree_update_start() was protecting
against. However, it's not actually needed because we don't allow
subsequent append writes to btree nodes until the node is reachable on
disk.

Dropping this unneeded pin also fixes a bug introduced by "bcachefs:
Journal seq now incremented at entry open, not close" - in the new code,
if the journal is completely empty a journal pin list for
journal_cur_seq() won't exist.

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

diff --git a/fs/bcachefs/btree_update_interior.c b/fs/bcachefs/btree_update_interior.c
index 17d65c9e2bd49526e2e0fd06327a670d4bd4a747..7e876a904c10f9e133e11435a2d32375838933d9 100644 (file)
--- a/fs/bcachefs/btree_update_interior.c
+++ b/fs/bcachefs/btree_update_interior.c
@@ -544,8 +544,6 @@ static void btree_update_nodes_written(struct btree_update *as)
        if (ret)
                goto err;
 
-       BUG_ON(!journal_pin_active(&as->journal));
-
        /*
         * Wait for any in flight writes to finish before we free the old nodes
         * on disk:
@@ -1045,10 +1043,6 @@ retry:
        if (ret)
                goto err;
 
-       bch2_journal_pin_add(&c->journal,
-                            atomic64_read(&c->journal.seq),
-                            &as->journal, NULL);
-
        return as;
 err:
        bch2_btree_update_free(as);