bcachefs: Fix rebalance from durability=0 device

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

diff --git a/fs/bcachefs/data_update.c b/fs/bcachefs/data_update.c
index 34731ee0217f62f6e43fb691e76083c46026b127..0022b51ce3c09cc9eafaab2f0639c944078d8c54 100644 (file)
--- a/fs/bcachefs/data_update.c
+++ b/fs/bcachefs/data_update.c
@@ -598,6 +598,8 @@ int bch2_data_update_init(struct btree_trans *trans,
                i++;
        }
 
+       unsigned durability_required = max(0, (int) (io_opts.data_replicas - durability_have));
+
        /*
         * If current extent durability is less than io_opts.data_replicas,
         * we're not trying to rereplicate the extent up to data_replicas here -
@@ -607,7 +609,7 @@ int bch2_data_update_init(struct btree_trans *trans,
         * rereplicate, currently, so that users don't get an unexpected -ENOSPC
         */
        if (!(m->data_opts.write_flags & BCH_WRITE_CACHED) &&
-           durability_have >= io_opts.data_replicas) {
+           !durability_required) {
                m->data_opts.kill_ptrs |= m->data_opts.rewrite_ptrs;
                m->data_opts.rewrite_ptrs = 0;
                /* if iter == NULL, it's just a promote */
@@ -616,11 +618,18 @@ int bch2_data_update_init(struct btree_trans *trans,
                goto done;
        }
 
-       m->op.nr_replicas = min(durability_removing, io_opts.data_replicas - durability_have) +
+       m->op.nr_replicas = min(durability_removing, durability_required) +
                m->data_opts.extra_replicas;
-       m->op.nr_replicas_required = m->op.nr_replicas;
 
-       BUG_ON(!m->op.nr_replicas);
+       /*
+        * If device(s) were set to durability=0 after data was written to them
+        * we can end up with a duribilty=0 extent, and the normal algorithm
+        * that tries not to increase durability doesn't work:
+        */
+       if (!(durability_have + durability_removing))
+               m->op.nr_replicas = max((unsigned) m->op.nr_replicas, 1);
+
+       m->op.nr_replicas_required = m->op.nr_replicas;
 
        if (reserve_sectors) {
                ret = bch2_disk_reservation_add(c, &m->op.res, reserve_sectors,