diff --git a/.bcachefs_revision b/.bcachefs_revision
index a0a4a343..d1024536 100644
--- a/.bcachefs_revision
+++ b/.bcachefs_revision
@@ -1 +1 @@
-e6fa8eaa1b374fc6262bd088ad1f140f4c5a8b11
+8d3093bd9b9254957badce4a4ff178baeb3632ed
diff --git a/include/linux/bsearch.h b/include/linux/bsearch.h
new file mode 100644
index 00000000..e66b711d
--- /dev/null
+++ b/include/linux/bsearch.h
@@ -0,0 +1,32 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_BSEARCH_H
+#define _LINUX_BSEARCH_H
+
+#include <linux/types.h>
+
+static __always_inline
+void *__inline_bsearch(const void *key, const void *base, size_t num, size_t size, cmp_func_t cmp)
+{
+	const char *pivot;
+	int result;
+
+	while (num > 0) {
+		pivot = base + (num >> 1) * size;
+		result = cmp(key, pivot);
+
+		if (result == 0)
+			return (void *)pivot;
+
+		if (result > 0) {
+			base = pivot + size;
+			num--;
+		}
+		num >>= 1;
+	}
+
+	return NULL;
+}
+
+extern void *bsearch(const void *key, const void *base, size_t num, size_t size, cmp_func_t cmp);
+
+#endif /* _LINUX_BSEARCH_H */
diff --git a/include/linux/types.h b/include/linux/types.h
index c9886cba..77f96737 100644
--- a/include/linux/types.h
+++ b/include/linux/types.h
@@ -76,4 +76,6 @@ typedef __u64 __bitwise __be64;
 
 typedef u64 sector_t;
 
+typedef int (*cmp_func_t)(const void *a, const void *b);
+
 #endif /* _TOOLS_LINUX_TYPES_H_ */
diff --git a/libbcachefs/bcachefs.h b/libbcachefs/bcachefs.h
index ce058d55..f2d2c7bb 100644
--- a/libbcachefs/bcachefs.h
+++ b/libbcachefs/bcachefs.h
@@ -485,10 +485,12 @@ enum {
 	BCH_FS_ALLOCATOR_RUNNING,
 	BCH_FS_ALLOCATOR_STOPPING,
 	BCH_FS_INITIAL_GC_DONE,
+	BCH_FS_INITIAL_GC_UNFIXED,
 	BCH_FS_BTREE_INTERIOR_REPLAY_DONE,
 	BCH_FS_FSCK_DONE,
 	BCH_FS_STARTED,
 	BCH_FS_RW,
+	BCH_FS_WAS_RW,
 
 	/* shutdown: */
 	BCH_FS_STOPPING,
@@ -497,7 +499,9 @@ enum {
 
 	/* errors: */
 	BCH_FS_ERROR,
+	BCH_FS_TOPOLOGY_ERROR,
 	BCH_FS_ERRORS_FIXED,
+	BCH_FS_ERRORS_NOT_FIXED,
 
 	/* misc: */
 	BCH_FS_NEED_ANOTHER_GC,
diff --git a/libbcachefs/bcachefs_format.h b/libbcachefs/bcachefs_format.h
index ead7268b..d640a311 100644
--- a/libbcachefs/bcachefs_format.h
+++ b/libbcachefs/bcachefs_format.h
@@ -1313,12 +1313,10 @@ LE64_BITMASK(BCH_SB_GRPQUOTA,		struct bch_sb, flags[0], 58, 59);
 LE64_BITMASK(BCH_SB_PRJQUOTA,		struct bch_sb, flags[0], 59, 60);
 
 LE64_BITMASK(BCH_SB_HAS_ERRORS,		struct bch_sb, flags[0], 60, 61);
+LE64_BITMASK(BCH_SB_HAS_TOPOLOGY_ERRORS,struct bch_sb, flags[0], 61, 62);
 
-/* bit 61 was reflink option */
 LE64_BITMASK(BCH_SB_BIG_ENDIAN,		struct bch_sb, flags[0], 62, 63);
 
-/* 61-64 unused */
-
 LE64_BITMASK(BCH_SB_STR_HASH_TYPE,	struct bch_sb, flags[1],  0,  4);
 LE64_BITMASK(BCH_SB_COMPRESSION_TYPE,	struct bch_sb, flags[1],  4,  8);
 LE64_BITMASK(BCH_SB_INODE_32BIT,	struct bch_sb, flags[1],  8,  9);
diff --git a/libbcachefs/btree_cache.c b/libbcachefs/btree_cache.c
index edc3c5ed..f8692f79 100644
--- a/libbcachefs/btree_cache.c
+++ b/libbcachefs/btree_cache.c
@@ -958,6 +958,36 @@ void bch2_btree_node_prefetch(struct bch_fs *c, struct btree_iter *iter,
 	bch2_btree_node_fill(c, iter, k, btree_id, level, SIX_LOCK_read, false);
 }
 
+void bch2_btree_node_evict(struct bch_fs *c, const struct bkey_i *k)
+{
+	struct btree_cache *bc = &c->btree_cache;
+	struct btree *b;
+
+	b = btree_cache_find(bc, k);
+	if (!b)
+		return;
+
+	six_lock_intent(&b->c.lock, NULL, NULL);
+	six_lock_write(&b->c.lock, NULL, NULL);
+
+	wait_on_bit_io(&b->flags, BTREE_NODE_read_in_flight,
+		       TASK_UNINTERRUPTIBLE);
+	__bch2_btree_node_write(c, b);
+
+	/* wait for any in flight btree write */
+	btree_node_wait_on_io(b);
+
+	BUG_ON(btree_node_dirty(b));
+
+	mutex_lock(&bc->lock);
+	btree_node_data_free(c, b);
+	bch2_btree_node_hash_remove(bc, b);
+	mutex_unlock(&bc->lock);
+
+	six_unlock_write(&b->c.lock);
+	six_unlock_intent(&b->c.lock);
+}
+
 void bch2_btree_node_to_text(struct printbuf *out, struct bch_fs *c,
 			     struct btree *b)
 {
diff --git a/libbcachefs/btree_cache.h b/libbcachefs/btree_cache.h
index c517cc02..40dd263a 100644
--- a/libbcachefs/btree_cache.h
+++ b/libbcachefs/btree_cache.h
@@ -30,6 +30,8 @@ struct btree *bch2_btree_node_get_noiter(struct bch_fs *, const struct bkey_i *,
 void bch2_btree_node_prefetch(struct bch_fs *, struct btree_iter *,
 			      const struct bkey_i *, enum btree_id, unsigned);
 
+void bch2_btree_node_evict(struct bch_fs *, const struct bkey_i *);
+
 void bch2_fs_btree_cache_exit(struct bch_fs *);
 int bch2_fs_btree_cache_init(struct bch_fs *);
 void bch2_fs_btree_cache_init_early(struct btree_cache *);
diff --git a/libbcachefs/btree_gc.c b/libbcachefs/btree_gc.c
index 864931ea..24fa279d 100644
--- a/libbcachefs/btree_gc.c
+++ b/libbcachefs/btree_gc.c
@@ -66,8 +66,6 @@ static int bch2_gc_check_topology(struct bch_fs *c,
 		? node_start
 		: bpos_successor(prev->k->k.p);
 	char buf1[200], buf2[200];
-	bool update_min = false;
-	bool update_max = false;
 	int ret = 0;
 
 	if (cur.k->k.type == KEY_TYPE_btree_ptr_v2) {
@@ -81,86 +79,343 @@ static int bch2_gc_check_topology(struct bch_fs *c,
 			bch2_bkey_val_to_text(&PBUF(buf1), c, bkey_i_to_s_c(prev->k));
 		}
 
-		if (fsck_err_on(bpos_cmp(expected_start, bp->v.min_key), c,
-				"btree node with incorrect min_key at btree %s level %u:\n"
-				"  prev %s\n"
-				"  cur %s",
-				bch2_btree_ids[b->c.btree_id], b->c.level,
-				buf1,
-				(bch2_bkey_val_to_text(&PBUF(buf2), c, bkey_i_to_s_c(cur.k)), buf2)))
-			update_min = true;
+		if (bpos_cmp(expected_start, bp->v.min_key)) {
+			bch2_topology_error(c);
+
+			if (fsck_err(c, "btree node with incorrect min_key at btree %s level %u:\n"
+				     "  prev %s\n"
+				     "  cur %s",
+				     bch2_btree_ids[b->c.btree_id], b->c.level,
+				     buf1,
+				     (bch2_bkey_val_to_text(&PBUF(buf2), c, bkey_i_to_s_c(cur.k)), buf2))) {
+				bch_info(c, "Halting mark and sweep to start topology repair pass");
+				return FSCK_ERR_START_TOPOLOGY_REPAIR;
+			} else {
+				set_bit(BCH_FS_INITIAL_GC_UNFIXED, &c->flags);
+			}
+		}
 	}
 
-	if (fsck_err_on(is_last &&
-			bpos_cmp(cur.k->k.p, node_end), c,
+	if (is_last && bpos_cmp(cur.k->k.p, node_end)) {
+		bch2_topology_error(c);
+
+		if (fsck_err(c, "btree node with incorrect max_key at btree %s level %u:\n"
+			     "  %s\n"
+			     "  expected %s",
+			     bch2_btree_ids[b->c.btree_id], b->c.level,
+			     (bch2_bkey_val_to_text(&PBUF(buf1), c, bkey_i_to_s_c(cur.k)), buf1),
+			     (bch2_bpos_to_text(&PBUF(buf2), node_end), buf2))) {
+			bch_info(c, "Halting mark and sweep to start topology repair pass");
+			return FSCK_ERR_START_TOPOLOGY_REPAIR;
+		} else {
+			set_bit(BCH_FS_INITIAL_GC_UNFIXED, &c->flags);
+		}
+	}
+
+	bch2_bkey_buf_copy(prev, c, cur.k);
+fsck_err:
+	return ret;
+}
+
+static void btree_ptr_to_v2(struct btree *b, struct bkey_i_btree_ptr_v2 *dst)
+{
+	switch (b->key.k.type) {
+	case KEY_TYPE_btree_ptr: {
+		struct bkey_i_btree_ptr *src = bkey_i_to_btree_ptr(&b->key);
+
+		dst->k.p		= src->k.p;
+		dst->v.mem_ptr		= 0;
+		dst->v.seq		= b->data->keys.seq;
+		dst->v.sectors_written	= 0;
+		dst->v.flags		= 0;
+		dst->v.min_key		= b->data->min_key;
+		set_bkey_val_bytes(&dst->k, sizeof(dst->v) + bkey_val_bytes(&src->k));
+		memcpy(dst->v.start, src->v.start, bkey_val_bytes(&src->k));
+		break;
+	}
+	case KEY_TYPE_btree_ptr_v2:
+		bkey_copy(&dst->k_i, &b->key);
+		break;
+	default:
+		BUG();
+	}
+}
+
+static int set_node_min(struct bch_fs *c, struct btree *b, struct bpos new_min)
+{
+	struct bkey_i_btree_ptr_v2 *new;
+	int ret;
+
+	new = kmalloc(BKEY_BTREE_PTR_U64s_MAX * sizeof(u64), GFP_KERNEL);
+	if (!new)
+		return -ENOMEM;
+
+	btree_ptr_to_v2(b, new);
+	b->data->min_key	= new_min;
+	new->v.min_key		= new_min;
+	SET_BTREE_PTR_RANGE_UPDATED(&new->v, true);
+
+	ret = bch2_journal_key_insert(c, b->c.btree_id, b->c.level + 1, &new->k_i);
+	if (ret) {
+		kfree(new);
+		return ret;
+	}
+
+	bch2_btree_node_drop_keys_outside_node(b);
+
+	return 0;
+}
+
+static int set_node_max(struct bch_fs *c, struct btree *b, struct bpos new_max)
+{
+	struct bkey_i_btree_ptr_v2 *new;
+	int ret;
+
+	ret = bch2_journal_key_delete(c, b->c.btree_id, b->c.level + 1, b->key.k.p);
+	if (ret)
+		return ret;
+
+	new = kmalloc(BKEY_BTREE_PTR_U64s_MAX * sizeof(u64), GFP_KERNEL);
+	if (!new)
+		return -ENOMEM;
+
+	btree_ptr_to_v2(b, new);
+	b->data->max_key	= new_max;
+	new->k.p		= new_max;
+	SET_BTREE_PTR_RANGE_UPDATED(&new->v, true);
+
+	ret = bch2_journal_key_insert(c, b->c.btree_id, b->c.level + 1, &new->k_i);
+	if (ret) {
+		kfree(new);
+		return ret;
+	}
+
+	bch2_btree_node_drop_keys_outside_node(b);
+
+	mutex_lock(&c->btree_cache.lock);
+	bch2_btree_node_hash_remove(&c->btree_cache, b);
+
+	bkey_copy(&b->key, &new->k_i);
+	ret = __bch2_btree_node_hash_insert(&c->btree_cache, b);
+	BUG_ON(ret);
+	mutex_unlock(&c->btree_cache.lock);
+	return 0;
+}
+
+static int btree_repair_node_start(struct bch_fs *c, struct btree *b,
+				   struct btree *prev, struct btree *cur)
+{
+	struct bpos expected_start = !prev
+		? b->data->min_key
+		: bpos_successor(prev->key.k.p);
+	char buf1[200], buf2[200];
+	int ret = 0;
+
+	if (!prev) {
+		struct printbuf out = PBUF(buf1);
+		pr_buf(&out, "start of node: ");
+		bch2_bpos_to_text(&out, b->data->min_key);
+	} else {
+		bch2_bkey_val_to_text(&PBUF(buf1), c, bkey_i_to_s_c(&prev->key));
+	}
+
+	if (mustfix_fsck_err_on(bpos_cmp(expected_start, cur->data->min_key), c,
+			"btree node with incorrect min_key at btree %s level %u:\n"
+			"  prev %s\n"
+			"  cur %s",
+			bch2_btree_ids[b->c.btree_id], b->c.level,
+			buf1,
+			(bch2_bkey_val_to_text(&PBUF(buf2), c, bkey_i_to_s_c(&cur->key)), buf2))) {
+		if (prev &&
+		    bpos_cmp(expected_start, cur->data->min_key) > 0 &&
+		    BTREE_NODE_SEQ(cur->data) > BTREE_NODE_SEQ(prev->data))
+			ret = set_node_max(c, prev,
+				bpos_predecessor(cur->data->min_key));
+		else
+			ret = set_node_min(c, cur, expected_start);
+		if (ret)
+			return ret;
+	}
+fsck_err:
+	return ret;
+}
+
+static int btree_repair_node_end(struct bch_fs *c, struct btree *b,
+				 struct btree *child)
+{
+	char buf1[200], buf2[200];
+	int ret = 0;
+
+	if (mustfix_fsck_err_on(bpos_cmp(child->key.k.p, b->key.k.p), c,
 			"btree node with incorrect max_key at btree %s level %u:\n"
 			"  %s\n"
 			"  expected %s",
 			bch2_btree_ids[b->c.btree_id], b->c.level,
-			(bch2_bkey_val_to_text(&PBUF(buf1), c, bkey_i_to_s_c(cur.k)), buf1),
-			(bch2_bpos_to_text(&PBUF(buf2), node_end), buf2)))
-		update_max = true;
-
-	bch2_bkey_buf_copy(prev, c, cur.k);
-
-	if (update_min || update_max) {
-		struct bkey_i *new;
-		struct bkey_i_btree_ptr_v2 *bp = NULL;
-		struct btree *n;
-
-		if (update_max) {
-			ret = bch2_journal_key_delete(c, b->c.btree_id,
-						      b->c.level, cur.k->k.p);
-			if (ret)
-				return ret;
-		}
-
-		new = kmalloc(bkey_bytes(&cur.k->k), GFP_KERNEL);
-		if (!new) {
-			bch_err(c, "%s: error allocating new key", __func__);
-			return -ENOMEM;
-		}
-
-		bkey_copy(new, cur.k);
-
-		if (new->k.type == KEY_TYPE_btree_ptr_v2)
-			bp = bkey_i_to_btree_ptr_v2(new);
-
-		if (update_min)
-			bp->v.min_key = expected_start;
-		if (update_max)
-			new->k.p = node_end;
-		if (bp)
-			SET_BTREE_PTR_RANGE_UPDATED(&bp->v, true);
-
-		ret = bch2_journal_key_insert(c, b->c.btree_id, b->c.level, new);
-		if (ret) {
-			kfree(new);
+			(bch2_bkey_val_to_text(&PBUF(buf1), c, bkey_i_to_s_c(&child->key)), buf1),
+			(bch2_bpos_to_text(&PBUF(buf2), b->key.k.p), buf2))) {
+		ret = set_node_max(c, child, b->key.k.p);
+		if (ret)
 			return ret;
-		}
-
-		n = bch2_btree_node_get_noiter(c, cur.k, b->c.btree_id,
-					       b->c.level - 1, true);
-		if (n) {
-			mutex_lock(&c->btree_cache.lock);
-			bch2_btree_node_hash_remove(&c->btree_cache, n);
-
-			bkey_copy(&n->key, new);
-			if (update_min)
-				n->data->min_key = expected_start;
-			if (update_max)
-				n->data->max_key = node_end;
-
-			ret = __bch2_btree_node_hash_insert(&c->btree_cache, n);
-			BUG_ON(ret);
-			mutex_unlock(&c->btree_cache.lock);
-			six_unlock_read(&n->c.lock);
-		}
 	}
 fsck_err:
 	return ret;
 }
 
+#define DROP_THIS_NODE		10
+
+static int bch2_btree_repair_topology_recurse(struct bch_fs *c, struct btree *b)
+{
+	struct btree_and_journal_iter iter;
+	struct bkey_s_c k;
+	struct bkey_buf tmp;
+	struct btree *prev = NULL, *cur = NULL;
+	bool have_child, dropped_children = false;
+	char buf[200];
+	int ret = 0;
+
+	if (!b->c.level)
+		return 0;
+again:
+	have_child = dropped_children = false;
+	bch2_bkey_buf_init(&tmp);
+	bch2_btree_and_journal_iter_init_node_iter(&iter, c, b);
+
+	while ((k = bch2_btree_and_journal_iter_peek(&iter)).k) {
+		bch2_btree_and_journal_iter_advance(&iter);
+		bch2_bkey_buf_reassemble(&tmp, c, k);
+
+		cur = bch2_btree_node_get_noiter(c, tmp.k,
+					b->c.btree_id, b->c.level - 1,
+					false);
+		ret = PTR_ERR_OR_ZERO(cur);
+
+		if (mustfix_fsck_err_on(ret == -EIO, c,
+				"Unreadable btree node at btree %s level %u:\n"
+				"  %s",
+				bch2_btree_ids[b->c.btree_id],
+				b->c.level - 1,
+				(bch2_bkey_val_to_text(&PBUF(buf), c, bkey_i_to_s_c(tmp.k)), buf))) {
+			bch2_btree_node_evict(c, tmp.k);
+			ret = bch2_journal_key_delete(c, b->c.btree_id,
+						      b->c.level, tmp.k->k.p);
+			if (ret)
+				goto err;
+			continue;
+		}
+
+		if (ret) {
+			bch_err(c, "%s: error %i getting btree node",
+				__func__, ret);
+			break;
+		}
+
+		ret = btree_repair_node_start(c, b, prev, cur);
+		if (prev)
+			six_unlock_read(&prev->c.lock);
+		prev = cur;
+		cur = NULL;
+
+		if (ret)
+			break;
+	}
+
+	if (!ret && !IS_ERR_OR_NULL(prev)) {
+		BUG_ON(cur);
+		ret = btree_repair_node_end(c, b, prev);
+	}
+
+	if (!IS_ERR_OR_NULL(prev))
+		six_unlock_read(&prev->c.lock);
+	prev = NULL;
+	if (!IS_ERR_OR_NULL(cur))
+		six_unlock_read(&cur->c.lock);
+	cur = NULL;
+
+	if (ret)
+		goto err;
+
+	bch2_btree_and_journal_iter_exit(&iter);
+	bch2_btree_and_journal_iter_init_node_iter(&iter, c, b);
+
+	while ((k = bch2_btree_and_journal_iter_peek(&iter)).k) {
+		bch2_bkey_buf_reassemble(&tmp, c, k);
+		bch2_btree_and_journal_iter_advance(&iter);
+
+		cur = bch2_btree_node_get_noiter(c, tmp.k,
+					b->c.btree_id, b->c.level - 1,
+					false);
+		ret = PTR_ERR_OR_ZERO(cur);
+
+		if (ret) {
+			bch_err(c, "%s: error %i getting btree node",
+				__func__, ret);
+			goto err;
+		}
+
+		ret = bch2_btree_repair_topology_recurse(c, cur);
+		six_unlock_read(&cur->c.lock);
+		cur = NULL;
+
+		if (ret == DROP_THIS_NODE) {
+			bch2_btree_node_evict(c, tmp.k);
+			ret = bch2_journal_key_delete(c, b->c.btree_id,
+						      b->c.level, tmp.k->k.p);
+			dropped_children = true;
+		}
+
+		if (ret)
+			goto err;
+
+		have_child = true;
+	}
+
+	if (mustfix_fsck_err_on(!have_child, c,
+			"empty interior btree node at btree %s level %u\n"
+			"  %s",
+			bch2_btree_ids[b->c.btree_id],
+			b->c.level,
+			(bch2_bkey_val_to_text(&PBUF(buf), c, bkey_i_to_s_c(&b->key)), buf)))
+		ret = DROP_THIS_NODE;
+err:
+fsck_err:
+	if (!IS_ERR_OR_NULL(prev))
+		six_unlock_read(&prev->c.lock);
+	if (!IS_ERR_OR_NULL(cur))
+		six_unlock_read(&cur->c.lock);
+
+	bch2_btree_and_journal_iter_exit(&iter);
+	bch2_bkey_buf_exit(&tmp, c);
+
+	if (!ret && dropped_children)
+		goto again;
+
+	return ret;
+}
+
+static int bch2_repair_topology(struct bch_fs *c)
+{
+	struct btree *b;
+	unsigned i;
+	int ret = 0;
+
+	for (i = 0; i < BTREE_ID_NR && !ret; i++) {
+		b = c->btree_roots[i].b;
+		if (btree_node_fake(b))
+			continue;
+
+		six_lock_read(&b->c.lock, NULL, NULL);
+		ret = bch2_btree_repair_topology_recurse(c, b);
+		six_unlock_read(&b->c.lock);
+
+		if (ret == DROP_THIS_NODE) {
+			bch_err(c, "empty btree root - repair unimplemented");
+			ret = FSCK_ERR_EXIT;
+		}
+	}
+
+	return ret;
+}
+
 static int bch2_check_fix_ptrs(struct bch_fs *c, enum btree_id btree_id,
 			       unsigned level, bool is_root,
 			       struct bkey_s_c *k)
@@ -483,6 +738,7 @@ static int bch2_gc_btree_init_recurse(struct bch_fs *c, struct btree *b,
 	struct bkey_s_c k;
 	struct bkey_buf cur, prev;
 	u8 max_stale = 0;
+	char buf[200];
 	int ret = 0;
 
 	bch2_btree_and_journal_iter_init_node_iter(&iter, c, b);
@@ -498,7 +754,7 @@ static int bch2_gc_btree_init_recurse(struct bch_fs *c, struct btree *b,
 				       &k, &max_stale, true);
 		if (ret) {
 			bch_err(c, "%s: error %i from bch2_gc_mark_key", __func__, ret);
-			break;
+			goto fsck_err;
 		}
 
 		if (b->c.level) {
@@ -511,7 +767,7 @@ static int bch2_gc_btree_init_recurse(struct bch_fs *c, struct btree *b,
 					&prev, cur,
 					!bch2_btree_and_journal_iter_peek(&iter).k);
 			if (ret)
-				break;
+				goto fsck_err;
 		} else {
 			bch2_btree_and_journal_iter_advance(&iter);
 		}
@@ -532,18 +788,25 @@ static int bch2_gc_btree_init_recurse(struct bch_fs *c, struct btree *b,
 						false);
 			ret = PTR_ERR_OR_ZERO(child);
 
-			if (fsck_err_on(ret == -EIO, c,
-					"unreadable btree node")) {
-				ret = bch2_journal_key_delete(c, b->c.btree_id,
-							      b->c.level, cur.k->k.p);
-				if (ret)
-					return ret;
+			if (ret == -EIO) {
+				bch2_topology_error(c);
 
-				set_bit(BCH_FS_NEED_ANOTHER_GC, &c->flags);
-				continue;
-			}
-
-			if (ret) {
+				if (fsck_err(c, "Unreadable btree node at btree %s level %u:\n"
+					"  %s",
+					bch2_btree_ids[b->c.btree_id],
+					b->c.level - 1,
+					(bch2_bkey_val_to_text(&PBUF(buf), c, bkey_i_to_s_c(cur.k)), buf))) {
+					ret = FSCK_ERR_START_TOPOLOGY_REPAIR;
+					bch_info(c, "Halting mark and sweep to start topology repair pass");
+					goto fsck_err;
+				} else {
+					/* Continue marking when opted to not
+					 * fix the error: */
+					ret = 0;
+					set_bit(BCH_FS_INITIAL_GC_UNFIXED, &c->flags);
+					continue;
+				}
+			} else if (ret) {
 				bch_err(c, "%s: error %i getting btree node",
 					__func__, ret);
 				break;
@@ -583,16 +846,20 @@ static int bch2_gc_btree_init(struct bch_fs *c,
 		return 0;
 
 	six_lock_read(&b->c.lock, NULL, NULL);
-	if (fsck_err_on(bpos_cmp(b->data->min_key, POS_MIN), c,
+	if (mustfix_fsck_err_on(bpos_cmp(b->data->min_key, POS_MIN), c,
 			"btree root with incorrect min_key: %s",
 			(bch2_bpos_to_text(&PBUF(buf), b->data->min_key), buf))) {
-		BUG();
+		bch_err(c, "repair unimplemented");
+		ret = FSCK_ERR_EXIT;
+		goto fsck_err;
 	}
 
-	if (fsck_err_on(bpos_cmp(b->data->max_key, POS_MAX), c,
+	if (mustfix_fsck_err_on(bpos_cmp(b->data->max_key, POS_MAX), c,
 			"btree root with incorrect max_key: %s",
 			(bch2_bpos_to_text(&PBUF(buf), b->data->max_key), buf))) {
-		BUG();
+		bch_err(c, "repair unimplemented");
+		ret = FSCK_ERR_EXIT;
+		goto fsck_err;
 	}
 
 	if (b->c.level >= target_depth)
@@ -607,7 +874,7 @@ static int bch2_gc_btree_init(struct bch_fs *c,
 fsck_err:
 	six_unlock_read(&b->c.lock);
 
-	if (ret)
+	if (ret < 0)
 		bch_err(c, "%s: ret %i", __func__, ret);
 	return ret;
 }
@@ -622,23 +889,20 @@ static int bch2_gc_btrees(struct bch_fs *c, bool initial, bool metadata_only)
 {
 	enum btree_id ids[BTREE_ID_NR];
 	unsigned i;
+	int ret = 0;
 
 	for (i = 0; i < BTREE_ID_NR; i++)
 		ids[i] = i;
 	bubble_sort(ids, BTREE_ID_NR, btree_id_gc_phase_cmp);
 
-	for (i = 0; i < BTREE_ID_NR; i++) {
-		enum btree_id id = ids[i];
-		int ret = initial
-			? bch2_gc_btree_init(c, id, metadata_only)
-			: bch2_gc_btree(c, id, initial, metadata_only);
-		if (ret) {
-			bch_err(c, "%s: ret %i", __func__, ret);
-			return ret;
-		}
-	}
+	for (i = 0; i < BTREE_ID_NR && !ret; i++)
+		ret = initial
+			? bch2_gc_btree_init(c, ids[i], metadata_only)
+			: bch2_gc_btree(c, ids[i], initial, metadata_only);
 
-	return 0;
+	if (ret < 0)
+		bch_err(c, "%s: ret %i", __func__, ret);
+	return ret;
 }
 
 static void mark_metadata_sectors(struct bch_fs *c, struct bch_dev *ca,
@@ -1025,7 +1289,27 @@ again:
 
 	bch2_mark_superblocks(c);
 
+	if (test_bit(BCH_FS_TOPOLOGY_ERROR, &c->flags) &&
+	    !test_bit(BCH_FS_INITIAL_GC_DONE, &c->flags) &&
+	    c->opts.fix_errors != FSCK_OPT_NO) {
+		bch_info(c, "starting topology repair pass");
+		ret = bch2_repair_topology(c);
+		if (ret)
+			goto out;
+		bch_info(c, "topology repair pass done");
+	}
+
 	ret = bch2_gc_btrees(c, initial, metadata_only);
+
+	if (ret == FSCK_ERR_START_TOPOLOGY_REPAIR &&
+	    !test_bit(BCH_FS_INITIAL_GC_DONE, &c->flags)) {
+		set_bit(BCH_FS_NEED_ANOTHER_GC, &c->flags);
+		ret = 0;
+	}
+
+	if (ret == FSCK_ERR_START_TOPOLOGY_REPAIR)
+		ret = FSCK_ERR_EXIT;
+
 	if (ret)
 		goto out;
 
diff --git a/libbcachefs/btree_io.c b/libbcachefs/btree_io.c
index 2de31a6b..e609bc49 100644
--- a/libbcachefs/btree_io.c
+++ b/libbcachefs/btree_io.c
@@ -558,6 +558,46 @@ out:									\
 
 #define btree_err_on(cond, ...)	((cond) ? btree_err(__VA_ARGS__) : false)
 
+/*
+ * When btree topology repair changes the start or end of a node, that might
+ * mean we have to drop keys that are no longer inside the node:
+ */
+void bch2_btree_node_drop_keys_outside_node(struct btree *b)
+{
+	struct bset_tree *t;
+
+	for_each_bset(b, t) {
+		struct bset *i = bset(b, t);
+		struct bkey_packed *k;
+
+		for (k = i->start; k != vstruct_last(i); k = bkey_next(k))
+			if (bkey_cmp_left_packed(b, k, &b->data->min_key) < 0)
+				break;
+
+		if (k != i->start) {
+			unsigned shift = (u64 *) k - (u64 *) i->start;
+
+			memmove_u64s_down(i->start, k,
+					  (u64 *) vstruct_end(i) - (u64 *) k);
+			i->u64s = cpu_to_le16(le16_to_cpu(i->u64s) - shift);
+			set_btree_bset_end(b, t);
+			bch2_bset_set_no_aux_tree(b, t);
+		}
+
+		for (k = i->start; k != vstruct_last(i); k = bkey_next(k))
+			if (bkey_cmp_left_packed(b, k, &b->data->max_key) > 0)
+				break;
+
+		if (k != vstruct_last(i)) {
+			i->u64s = cpu_to_le16((u64 *) k - (u64 *) i->start);
+			set_btree_bset_end(b, t);
+			bch2_bset_set_no_aux_tree(b, t);
+		}
+	}
+
+	bch2_btree_build_aux_trees(b);
+}
+
 static int validate_bset(struct bch_fs *c, struct bch_dev *ca,
 			 struct btree *b, struct bset *i,
 			 unsigned sectors, int write, bool have_retry)
@@ -680,6 +720,8 @@ static int validate_bset_keys(struct bch_fs *c, struct btree *b,
 {
 	unsigned version = le16_to_cpu(i->version);
 	struct bkey_packed *k, *prev = NULL;
+	bool updated_range = b->key.k.type == KEY_TYPE_btree_ptr_v2 &&
+		BTREE_PTR_RANGE_UPDATED(&bkey_i_to_btree_ptr_v2(&b->key)->v);
 	int ret = 0;
 
 	for (k = i->start;
@@ -713,7 +755,7 @@ static int validate_bset_keys(struct bch_fs *c, struct btree *b,
 		u = __bkey_disassemble(b, k, &tmp);
 
 		invalid = __bch2_bkey_invalid(c, u.s_c, btree_node_type(b)) ?:
-			bch2_bkey_in_btree_node(b, u.s_c) ?:
+			(!updated_range ?  bch2_bkey_in_btree_node(b, u.s_c) : NULL) ?:
 			(write ? bch2_bkey_val_invalid(c, u.s_c) : NULL);
 		if (invalid) {
 			char buf[160];
@@ -770,6 +812,8 @@ int bch2_btree_node_read_done(struct bch_fs *c, struct bch_dev *ca,
 	struct bch_extent_ptr *ptr;
 	struct bset *i;
 	bool used_mempool, blacklisted;
+	bool updated_range = b->key.k.type == KEY_TYPE_btree_ptr_v2 &&
+		BTREE_PTR_RANGE_UPDATED(&bkey_i_to_btree_ptr_v2(&b->key)->v);
 	unsigned u64s;
 	int ret, retry_read = 0, write = READ;
 
@@ -917,6 +961,9 @@ int bch2_btree_node_read_done(struct bch_fs *c, struct bch_dev *ca,
 
 	btree_bounce_free(c, btree_bytes(c), used_mempool, sorted);
 
+	if (updated_range)
+		bch2_btree_node_drop_keys_outside_node(b);
+
 	i = &b->data->keys;
 	for (k = i->start; k != vstruct_last(i);) {
 		struct bkey tmp;
@@ -986,6 +1033,7 @@ static void btree_node_read_work(struct work_struct *work)
 	struct bch_io_failures failed = { .nr = 0 };
 	char buf[200];
 	struct printbuf out;
+	bool saw_error = false;
 	bool can_retry;
 
 	goto start;
@@ -1023,6 +1071,8 @@ start:
 		    !bch2_btree_node_read_done(c, ca, b, can_retry))
 			break;
 
+		saw_error = true;
+
 		if (!can_retry) {
 			set_btree_node_read_error(b);
 			break;
@@ -1032,6 +1082,10 @@ start:
 	bch2_time_stats_update(&c->times[BCH_TIME_btree_node_read],
 			       rb->start_time);
 	bio_put(&rb->bio);
+
+	if (saw_error && !btree_node_read_error(b))
+		bch2_btree_node_rewrite_async(c, b);
+
 	clear_btree_node_read_in_flight(b);
 	wake_up_bit(&b->flags, BTREE_NODE_read_in_flight);
 }
diff --git a/libbcachefs/btree_io.h b/libbcachefs/btree_io.h
index c8a8b05a..cadcf7f8 100644
--- a/libbcachefs/btree_io.h
+++ b/libbcachefs/btree_io.h
@@ -131,6 +131,8 @@ static inline void bset_encrypt(struct bch_fs *c, struct bset *i, unsigned offse
 
 void bch2_btree_sort_into(struct bch_fs *, struct btree *, struct btree *);
 
+void bch2_btree_node_drop_keys_outside_node(struct btree *);
+
 void bch2_btree_build_aux_trees(struct btree *);
 void bch2_btree_init_next(struct bch_fs *, struct btree *,
 			 struct btree_iter *);
diff --git a/libbcachefs/btree_key_cache.c b/libbcachefs/btree_key_cache.c
index a5181a96..a0ff0c3c 100644
--- a/libbcachefs/btree_key_cache.c
+++ b/libbcachefs/btree_key_cache.c
@@ -682,7 +682,9 @@ void bch2_fs_btree_key_cache_exit(struct btree_key_cache *bc)
 		kmem_cache_free(bch2_key_cache, ck);
 	}
 
-	BUG_ON(atomic_long_read(&bc->nr_dirty) && !bch2_journal_error(&c->journal));
+	BUG_ON(atomic_long_read(&bc->nr_dirty) &&
+	       !bch2_journal_error(&c->journal) &&
+	       test_bit(BCH_FS_WAS_RW, &c->flags));
 	BUG_ON(atomic_long_read(&bc->nr_keys));
 
 	mutex_unlock(&bc->lock);
diff --git a/libbcachefs/btree_update.h b/libbcachefs/btree_update.h
index 0c7caa7e..56131ac5 100644
--- a/libbcachefs/btree_update.h
+++ b/libbcachefs/btree_update.h
@@ -72,6 +72,7 @@ int bch2_btree_delete_range(struct bch_fs *, enum btree_id,
 
 int bch2_btree_node_rewrite(struct bch_fs *c, struct btree_iter *,
 			    __le64, unsigned);
+void bch2_btree_node_rewrite_async(struct bch_fs *, struct btree *);
 int bch2_btree_node_update_key(struct bch_fs *, struct btree_iter *,
 			       struct btree *, struct bkey_i *);
 
diff --git a/libbcachefs/btree_update_interior.c b/libbcachefs/btree_update_interior.c
index 5c86e76f..b9e0ff97 100644
--- a/libbcachefs/btree_update_interior.c
+++ b/libbcachefs/btree_update_interior.c
@@ -1154,6 +1154,27 @@ static void bch2_insert_fixup_btree_ptr(struct btree_update *as, struct btree *b
 	set_btree_node_need_write(b);
 }
 
+static void
+__bch2_btree_insert_keys_interior(struct btree_update *as, struct btree *b,
+				  struct btree_iter *iter, struct keylist *keys,
+				  struct btree_node_iter node_iter)
+{
+	struct bkey_i *insert = bch2_keylist_front(keys);
+	struct bkey_packed *k;
+
+	BUG_ON(btree_node_type(b) != BKEY_TYPE_btree);
+
+	while ((k = bch2_btree_node_iter_prev_all(&node_iter, b)) &&
+	       (bkey_cmp_left_packed(b, k, &insert->k.p) >= 0))
+		;
+
+	while (!bch2_keylist_empty(keys)) {
+		bch2_insert_fixup_btree_ptr(as, b, iter,
+				bch2_keylist_front(keys), &node_iter);
+		bch2_keylist_pop_front(keys);
+	}
+}
+
 /*
  * Move keys from n1 (original replacement node, now lower node) to n2 (higher
  * node)
@@ -1284,16 +1305,9 @@ static void btree_split_insert_keys(struct btree_update *as, struct btree *b,
 	struct bkey_packed *src, *dst, *n;
 	struct bset *i;
 
-	BUG_ON(btree_node_type(b) != BKEY_TYPE_btree);
-
 	bch2_btree_node_iter_init(&node_iter, b, &k->k.p);
 
-	while (!bch2_keylist_empty(keys)) {
-		k = bch2_keylist_front(keys);
-
-		bch2_insert_fixup_btree_ptr(as, b, iter, k, &node_iter);
-		bch2_keylist_pop_front(keys);
-	}
+	__bch2_btree_insert_keys_interior(as, b, iter, keys, node_iter);
 
 	/*
 	 * We can't tolerate whiteouts here - with whiteouts there can be
@@ -1439,24 +1453,8 @@ bch2_btree_insert_keys_interior(struct btree_update *as, struct btree *b,
 				struct btree_iter *iter, struct keylist *keys)
 {
 	struct btree_iter *linked;
-	struct btree_node_iter node_iter;
-	struct bkey_i *insert = bch2_keylist_front(keys);
-	struct bkey_packed *k;
 
-	/* Don't screw up @iter's position: */
-	node_iter = iter->l[b->c.level].iter;
-
-	/*
-	 * btree_split(), btree_gc_coalesce() will insert keys before
-	 * the iterator's current position - they know the keys go in
-	 * the node the iterator points to:
-	 */
-	while ((k = bch2_btree_node_iter_prev_all(&node_iter, b)) &&
-	       (bkey_cmp_left_packed(b, k, &insert->k.p) >= 0))
-		;
-
-	for_each_keylist_key(keys, insert)
-		bch2_insert_fixup_btree_ptr(as, b, iter, insert, &node_iter);
+	__bch2_btree_insert_keys_interior(as, b, iter, keys, iter->l[b->c.level].iter);
 
 	btree_update_updated_node(as, b);
 
@@ -1611,11 +1609,12 @@ retry:
 
 		bch2_bpos_to_text(&PBUF(buf1), prev->data->max_key);
 		bch2_bpos_to_text(&PBUF(buf2), next->data->min_key);
-		bch2_fs_inconsistent(c,
-				     "btree topology error in btree merge:\n"
-				     "prev ends at   %s\n"
-				     "next starts at %s\n",
-				     buf1, buf2);
+		bch_err(c,
+			"btree topology error in btree merge:\n"
+			"  prev ends at   %s\n"
+			"  next starts at %s",
+			buf1, buf2);
+		bch2_topology_error(c);
 		ret = -EIO;
 		goto err;
 	}
@@ -1797,6 +1796,56 @@ out:
 	return ret;
 }
 
+struct async_btree_rewrite {
+	struct bch_fs		*c;
+	struct work_struct	work;
+	enum btree_id		btree_id;
+	unsigned		level;
+	struct bpos		pos;
+	__le64			seq;
+};
+
+void async_btree_node_rewrite_work(struct work_struct *work)
+{
+	struct async_btree_rewrite *a =
+		container_of(work, struct async_btree_rewrite, work);
+	struct bch_fs *c = a->c;
+	struct btree_trans trans;
+	struct btree_iter *iter;
+
+	bch2_trans_init(&trans, c, 0, 0);
+	iter = bch2_trans_get_node_iter(&trans, a->btree_id, a->pos,
+					BTREE_MAX_DEPTH, a->level, 0);
+	bch2_btree_node_rewrite(c, iter, a->seq, 0);
+	bch2_trans_iter_put(&trans, iter);
+	bch2_trans_exit(&trans);
+	percpu_ref_put(&c->writes);
+	kfree(a);
+}
+
+void bch2_btree_node_rewrite_async(struct bch_fs *c, struct btree *b)
+{
+	struct async_btree_rewrite *a = kmalloc(sizeof(*a), GFP_NOFS);
+
+	if (!percpu_ref_tryget(&c->writes))
+		return;
+
+	a = kmalloc(sizeof(*a), GFP_NOFS);
+	if (!a) {
+		percpu_ref_put(&c->writes);
+		return;
+	}
+
+	a->c		= c;
+	a->btree_id	= b->c.btree_id;
+	a->level	= b->c.level;
+	a->pos		= b->key.k.p;
+	a->seq		= b->data->keys.seq;
+
+	INIT_WORK(&a->work, async_btree_node_rewrite_work);
+	queue_work(system_long_wq, &a->work);
+}
+
 static void __bch2_btree_node_update_key(struct bch_fs *c,
 					 struct btree_update *as,
 					 struct btree_iter *iter,
diff --git a/libbcachefs/error.c b/libbcachefs/error.c
index a8ee1db8..90c3b986 100644
--- a/libbcachefs/error.c
+++ b/libbcachefs/error.c
@@ -25,6 +25,13 @@ bool bch2_inconsistent_error(struct bch_fs *c)
 	}
 }
 
+void bch2_topology_error(struct bch_fs *c)
+{
+	set_bit(BCH_FS_TOPOLOGY_ERROR, &c->flags);
+	if (test_bit(BCH_FS_INITIAL_GC_DONE, &c->flags))
+		bch2_inconsistent_error(c);
+}
+
 void bch2_fatal_error(struct bch_fs *c)
 {
 	if (bch2_fs_emergency_read_only(c))
@@ -74,9 +81,13 @@ enum fsck_err_ret bch2_fsck_err(struct bch_fs *c, unsigned flags,
 		vprintk(fmt, args);
 		va_end(args);
 
-		return bch2_inconsistent_error(c)
-			? FSCK_ERR_EXIT
-			: FSCK_ERR_FIX;
+		if (c->opts.errors == BCH_ON_ERROR_continue) {
+			bch_err(c, "fixing");
+			return FSCK_ERR_FIX;
+		} else {
+			bch2_inconsistent_error(c);
+			return FSCK_ERR_EXIT;
+		}
 	}
 
 	mutex_lock(&c->fsck_error_lock);
@@ -146,6 +157,7 @@ print:
 		set_bit(BCH_FS_ERRORS_FIXED, &c->flags);
 		return FSCK_ERR_FIX;
 	} else {
+		set_bit(BCH_FS_ERRORS_NOT_FIXED, &c->flags);
 		set_bit(BCH_FS_ERROR, &c->flags);
 		return c->opts.fix_errors == FSCK_OPT_EXIT ||
 			!(flags & FSCK_CAN_IGNORE)
diff --git a/libbcachefs/error.h b/libbcachefs/error.h
index 0e49fd72..d8cd19b3 100644
--- a/libbcachefs/error.h
+++ b/libbcachefs/error.h
@@ -29,6 +29,8 @@ struct work_struct;
 
 bool bch2_inconsistent_error(struct bch_fs *);
 
+void bch2_topology_error(struct bch_fs *);
+
 #define bch2_fs_inconsistent(c, ...)					\
 ({									\
 	bch_err(c, __VA_ARGS__);					\
@@ -88,6 +90,7 @@ enum fsck_err_ret {
 	FSCK_ERR_IGNORE	= 0,
 	FSCK_ERR_FIX	= 1,
 	FSCK_ERR_EXIT	= 2,
+	FSCK_ERR_START_TOPOLOGY_REPAIR = 3,
 };
 
 struct fsck_err_state {
diff --git a/libbcachefs/fsck.c b/libbcachefs/fsck.c
index 26fbd8c2..338d50be 100644
--- a/libbcachefs/fsck.c
+++ b/libbcachefs/fsck.c
@@ -12,8 +12,8 @@
 #include "super.h"
 #include "xattr.h"
 
+#include <linux/bsearch.h>
 #include <linux/dcache.h> /* struct qstr */
-#include <linux/generic-radix-tree.h>
 
 #define QSTR(n) { { { .len = strlen(n) } }, .name = n }
 
@@ -290,21 +290,24 @@ static int hash_redo_key(struct btree_trans *trans,
 			 struct bch_hash_info *hash_info,
 			 struct btree_iter *k_iter, struct bkey_s_c k)
 {
-	struct bkey_i delete;
+	struct bkey_i *delete;
 	struct bkey_i *tmp;
 
+	delete = bch2_trans_kmalloc(trans, sizeof(*delete));
+	if (IS_ERR(delete))
+		return PTR_ERR(delete);
+
 	tmp = bch2_trans_kmalloc(trans, bkey_bytes(k.k));
 	if (IS_ERR(tmp))
 		return PTR_ERR(tmp);
 
 	bkey_reassemble(tmp, k);
 
-	bkey_init(&delete.k);
-	delete.k.p = k_iter->pos;
-	bch2_trans_update(trans, k_iter, &delete, 0);
+	bkey_init(&delete->k);
+	delete->k.p = k_iter->pos;
+	bch2_trans_update(trans, k_iter, delete, 0);
 
-	return bch2_hash_set(trans, desc, hash_info, k_iter->pos.inode,
-			     tmp, 0);
+	return bch2_hash_set(trans, desc, hash_info, k_iter->pos.inode, tmp, 0);
 }
 
 static int fsck_hash_delete_at(struct btree_trans *trans,
@@ -377,9 +380,8 @@ static int hash_check_key(struct btree_trans *trans,
 	return ret;
 bad_hash:
 	if (fsck_err(c, "hash table key at wrong offset: btree %u inode %llu offset %llu, "
-		     "hashed to %llu should be at %llu\n%s",
-		     desc.btree_id, hash_k.k->p.inode, hash_k.k->p.offset,
-		     hash, iter->pos.offset,
+		     "hashed to %llu\n%s",
+		     desc.btree_id, hash_k.k->p.inode, hash_k.k->p.offset, hash,
 		     (bch2_bkey_val_to_text(&PBUF(buf), c, hash_k), buf)) == FSCK_ERR_IGNORE)
 		return 0;
 
@@ -1130,38 +1132,120 @@ static int check_directory_structure(struct bch_fs *c)
 	return bch2_trans_exit(&trans) ?: ret;
 }
 
-struct nlink {
-	u32	count;
+struct nlink_table {
+	size_t		nr;
+	size_t		size;
+
+	struct nlink {
+		u64	inum;
+		u32	snapshot;
+		u32	count;
+	}		*d;
 };
 
-typedef GENRADIX(struct nlink) nlink_table;
-
-static void inc_link(struct bch_fs *c, nlink_table *links,
-		     u64 range_start, u64 *range_end, u64 inum)
+static int add_nlink(struct nlink_table *t, u64 inum, u32 snapshot)
 {
-	struct nlink *link;
+	if (t->nr == t->size) {
+		size_t new_size = max_t(size_t, 128UL, t->size * 2);
+		void *d = kvmalloc(new_size * sizeof(t->d[0]), GFP_KERNEL);
+		if (!d) {
+			return -ENOMEM;
+		}
 
-	if (inum < range_start || inum >= *range_end)
-		return;
+		memcpy(d, t->d, t->size * sizeof(t->d[0]));
+		kvfree(t->d);
 
-	if (inum - range_start >= SIZE_MAX / sizeof(struct nlink)) {
-		*range_end = inum;
-		return;
+		t->d = d;
+		t->size = new_size;
 	}
 
-	link = genradix_ptr_alloc(links, inum - range_start, GFP_KERNEL);
-	if (!link) {
-		bch_verbose(c, "allocation failed during fsck - will need another pass");
-		*range_end = inum;
-		return;
-	}
 
-	link->count++;
+	t->d[t->nr++] = (struct nlink) {
+		.inum		= inum,
+		.snapshot	= snapshot,
+	};
+
+	return 0;
+}
+
+static int nlink_cmp(const void *_l, const void *_r)
+{
+	const struct nlink *l = _l;
+	const struct nlink *r = _r;
+
+	return cmp_int(l->inum, r->inum) ?: cmp_int(l->snapshot, r->snapshot);
+}
+
+static void inc_link(struct bch_fs *c, struct nlink_table *links,
+		     u64 range_start, u64 range_end, u64 inum)
+{
+	struct nlink *link, key = {
+		.inum = inum, .snapshot = U32_MAX,
+	};
+
+	if (inum < range_start || inum >= range_end)
+		return;
+
+	link = __inline_bsearch(&key, links->d, links->nr,
+				sizeof(links->d[0]), nlink_cmp);
+	if (link)
+		link->count++;
 }
 
 noinline_for_stack
-static int bch2_gc_walk_dirents(struct bch_fs *c, nlink_table *links,
-			       u64 range_start, u64 *range_end)
+static int check_nlinks_find_hardlinks(struct bch_fs *c,
+				       struct nlink_table *t,
+				       u64 start, u64 *end)
+{
+	struct btree_trans trans;
+	struct btree_iter *iter;
+	struct bkey_s_c k;
+	struct bkey_s_c_inode inode;
+	struct bch_inode_unpacked u;
+	int ret = 0;
+
+	bch2_trans_init(&trans, c, BTREE_ITER_MAX, 0);
+
+	for_each_btree_key(&trans, iter, BTREE_ID_inodes,
+			   POS(0, start), 0, k, ret) {
+		if (k.k->type != KEY_TYPE_inode)
+			continue;
+
+		inode = bkey_s_c_to_inode(k);
+
+		/*
+		 * Backpointer and directory structure checks are sufficient for
+		 * directories, since they can't have hardlinks:
+		 */
+		if (S_ISDIR(le16_to_cpu(inode.v->bi_mode)))
+			continue;
+
+		/* Should never fail, checked by bch2_inode_invalid: */
+		BUG_ON(bch2_inode_unpack(inode, &u));
+
+		if (!u.bi_nlink)
+			continue;
+
+		ret = add_nlink(t, k.k->p.offset, k.k->p.snapshot);
+		if (ret) {
+			*end = k.k->p.offset;
+			ret = 0;
+			break;
+		}
+
+	}
+	bch2_trans_iter_put(&trans, iter);
+	bch2_trans_exit(&trans);
+
+	if (ret)
+		bch_err(c, "error in fsck: btree error %i while walking inodes", ret);
+
+	return ret;
+}
+
+noinline_for_stack
+static int check_nlinks_walk_dirents(struct bch_fs *c, struct nlink_table *links,
+				     u64 range_start, u64 range_end)
 {
 	struct btree_trans trans;
 	struct btree_iter *iter;
@@ -1193,80 +1277,58 @@ static int bch2_gc_walk_dirents(struct bch_fs *c, nlink_table *links,
 	return ret;
 }
 
-static int check_inode_nlink(struct btree_trans *trans,
-			     struct btree_iter *iter,
-			     struct bkey_s_c_inode inode,
-			     unsigned nlink)
-{
-	struct bch_fs *c = trans->c;
-	struct bch_inode_unpacked u;
-	int ret = 0;
-
-	/*
-	 * Backpointer and directory structure checks are sufficient for
-	 * directories, since they can't have hardlinks:
-	 */
-	if (S_ISDIR(le16_to_cpu(inode.v->bi_mode)))
-		return 0;
-
-	if (!nlink) {
-		bch_err(c, "no links found to inode %llu", inode.k->p.offset);
-		return -EINVAL;
-	}
-
-	ret = bch2_inode_unpack(inode, &u);
-
-	/* Should never happen, checked by bch2_inode_invalid: */
-	if (bch2_fs_inconsistent_on(ret, c,
-			 "error unpacking inode %llu in fsck",
-			 inode.k->p.inode))
-		return ret;
-
-	if (fsck_err_on(bch2_inode_nlink_get(&u) != nlink, c,
-			"inode %llu has wrong i_nlink (type %u i_nlink %u, should be %u)",
-			u.bi_inum, mode_to_type(u.bi_mode),
-			bch2_inode_nlink_get(&u), nlink)) {
-		bch2_inode_nlink_set(&u, nlink);
-
-		ret = __bch2_trans_do(trans, NULL, NULL,
-				      BTREE_INSERT_NOFAIL|
-				      BTREE_INSERT_LAZY_RW,
-				bch2_inode_write(trans, iter, &u));
-		if (ret)
-			bch_err(c, "error in fsck: error %i updating inode", ret);
-	}
-fsck_err:
-	return ret;
-}
-
 noinline_for_stack
-static int bch2_gc_walk_inodes(struct bch_fs *c,
-			       nlink_table *links,
+static int check_nlinks_update_hardlinks(struct bch_fs *c,
+			       struct nlink_table *links,
 			       u64 range_start, u64 range_end)
 {
 	struct btree_trans trans;
 	struct btree_iter *iter;
 	struct bkey_s_c k;
-	struct nlink *link;
+	struct bkey_s_c_inode inode;
+	struct bch_inode_unpacked u;
+	struct nlink *link = links->d;
 	int ret = 0;
 
 	bch2_trans_init(&trans, c, BTREE_ITER_MAX, 0);
 
 	for_each_btree_key(&trans, iter, BTREE_ID_inodes,
 			   POS(0, range_start), 0, k, ret) {
-		if (!k.k || k.k->p.offset >= range_end)
+		if (k.k->p.offset >= range_end)
 			break;
 
 		if (k.k->type != KEY_TYPE_inode)
 			continue;
 
-		link = genradix_ptr(links, k.k->p.offset - range_start);
-		ret = check_inode_nlink(&trans, iter,
-					bkey_s_c_to_inode(k), link ? link->count : 0);
-		if (ret)
-			break;
+		inode = bkey_s_c_to_inode(k);
+		if (S_ISDIR(le16_to_cpu(inode.v->bi_mode)))
+			continue;
 
+		BUG_ON(bch2_inode_unpack(inode, &u));
+
+		if (!u.bi_nlink)
+			continue;
+
+		while (link->inum < k.k->p.offset) {
+			link++;
+			BUG_ON(link >= links->d + links->nr);
+		}
+
+		if (fsck_err_on(bch2_inode_nlink_get(&u) != link->count, c,
+				"inode %llu has wrong i_nlink (type %u i_nlink %u, should be %u)",
+				u.bi_inum, mode_to_type(u.bi_mode),
+				bch2_inode_nlink_get(&u), link->count)) {
+			bch2_inode_nlink_set(&u, link->count);
+
+			ret = __bch2_trans_do(&trans, NULL, NULL,
+					      BTREE_INSERT_NOFAIL|
+					      BTREE_INSERT_LAZY_RW,
+					bch2_inode_write(&trans, iter, &u));
+			if (ret)
+				bch_err(c, "error in fsck: error %i updating inode", ret);
+		}
 	}
+fsck_err:
 	bch2_trans_iter_put(&trans, iter);
 	bch2_trans_exit(&trans);
 
@@ -1279,34 +1341,36 @@ static int bch2_gc_walk_inodes(struct bch_fs *c,
 noinline_for_stack
 static int check_nlinks(struct bch_fs *c)
 {
-	nlink_table links;
+	struct nlink_table links = { 0 };
 	u64 this_iter_range_start, next_iter_range_start = 0;
 	int ret = 0;
 
 	bch_verbose(c, "checking inode nlinks");
 
-	genradix_init(&links);
-
 	do {
 		this_iter_range_start = next_iter_range_start;
 		next_iter_range_start = U64_MAX;
 
-		ret = bch2_gc_walk_dirents(c, &links,
+		ret = check_nlinks_find_hardlinks(c, &links,
+						  this_iter_range_start,
+						  &next_iter_range_start);
+
+		ret = check_nlinks_walk_dirents(c, &links,
 					  this_iter_range_start,
-					  &next_iter_range_start);
+					  next_iter_range_start);
 		if (ret)
 			break;
 
-		ret = bch2_gc_walk_inodes(c, &links,
+		ret = check_nlinks_update_hardlinks(c, &links,
 					 this_iter_range_start,
 					 next_iter_range_start);
 		if (ret)
 			break;
 
-		genradix_free(&links);
+		links.nr = 0;
 	} while (next_iter_range_start != U64_MAX);
 
-	genradix_free(&links);
+	kvfree(links.d);
 
 	return ret;
 }
diff --git a/libbcachefs/recovery.c b/libbcachefs/recovery.c
index 2dc3dee4..a9ccd14e 100644
--- a/libbcachefs/recovery.c
+++ b/libbcachefs/recovery.c
@@ -973,7 +973,7 @@ int bch2_fs_recovery(struct bch_fs *c)
 	struct jset *last_journal_entry = NULL;
 	u64 blacklist_seq, journal_seq;
 	bool write_sb = false;
-	int ret;
+	int ret = 0;
 
 	if (c->sb.clean)
 		clean = read_superblock_clean(c);
@@ -1241,8 +1241,9 @@ use_clean:
 
 	if (c->opts.fsck &&
 	    !test_bit(BCH_FS_ERROR, &c->flags) &&
-	    BCH_SB_HAS_ERRORS(c->disk_sb.sb)) {
+	    !test_bit(BCH_FS_ERRORS_NOT_FIXED, &c->flags)) {
 		SET_BCH_SB_HAS_ERRORS(c->disk_sb.sb, 0);
+		SET_BCH_SB_HAS_TOPOLOGY_ERRORS(c->disk_sb.sb, 0);
 		write_sb = true;
 	}
 
@@ -1253,10 +1254,9 @@ use_clean:
 	if (c->journal_seq_blacklist_table &&
 	    c->journal_seq_blacklist_table->nr > 128)
 		queue_work(system_long_wq, &c->journal_seq_blacklist_gc_work);
-out:
+
 	ret = 0;
-err:
-fsck_err:
+out:
 	set_bit(BCH_FS_FSCK_DONE, &c->flags);
 	bch2_flush_fsck_errs(c);
 
@@ -1270,6 +1270,10 @@ fsck_err:
 	else
 		bch_verbose(c, "ret %i", ret);
 	return ret;
+err:
+fsck_err:
+	bch2_fs_emergency_read_only(c);
+	goto out;
 }
 
 int bch2_fs_initialize(struct bch_fs *c)
diff --git a/libbcachefs/super-io.c b/libbcachefs/super-io.c
index de8d49e3..11d7167b 100644
--- a/libbcachefs/super-io.c
+++ b/libbcachefs/super-io.c
@@ -433,6 +433,11 @@ int bch2_sb_to_fs(struct bch_fs *c, struct bch_sb *src)
 
 	__copy_super(&c->disk_sb, src);
 
+	if (BCH_SB_HAS_ERRORS(c->disk_sb.sb))
+		set_bit(BCH_FS_ERROR, &c->flags);
+	if (BCH_SB_HAS_TOPOLOGY_ERRORS(c->disk_sb.sb))
+		set_bit(BCH_FS_TOPOLOGY_ERROR, &c->flags);
+
 	ret = bch2_sb_replicas_to_cpu_replicas(c);
 	if (ret)
 		return ret;
@@ -713,6 +718,8 @@ int bch2_write_super(struct bch_fs *c)
 
 	if (test_bit(BCH_FS_ERROR, &c->flags))
 		SET_BCH_SB_HAS_ERRORS(c->disk_sb.sb, 1);
+	if (test_bit(BCH_FS_TOPOLOGY_ERROR, &c->flags))
+		SET_BCH_SB_HAS_TOPOLOGY_ERRORS(c->disk_sb.sb, 1);
 
 	SET_BCH_SB_BIG_ENDIAN(c->disk_sb.sb, CPU_BIG_ENDIAN);
 
diff --git a/libbcachefs/super.c b/libbcachefs/super.c
index b6e449a7..fd8a2991 100644
--- a/libbcachefs/super.c
+++ b/libbcachefs/super.c
@@ -381,6 +381,11 @@ static int __bch2_fs_read_write(struct bch_fs *c, bool early)
 	unsigned i;
 	int ret;
 
+	if (test_bit(BCH_FS_INITIAL_GC_UNFIXED, &c->flags)) {
+		bch_err(c, "cannot go rw, unfixed btree errors");
+		return -EROFS;
+	}
+
 	if (test_bit(BCH_FS_RW, &c->flags))
 		return 0;
 
@@ -440,6 +445,7 @@ static int __bch2_fs_read_write(struct bch_fs *c, bool early)
 
 	percpu_ref_reinit(&c->writes);
 	set_bit(BCH_FS_RW, &c->flags);
+	set_bit(BCH_FS_WAS_RW, &c->flags);
 	return 0;
 err:
 	__bch2_fs_read_only(c);