bcachefs: Kill bch2_verify_bucket_evacuated()

With backpointers, it's now impossible for bch2_evacuate_bucket() to be
completely reliable: it can race with an extent being partially
overwritten or split, which needs a new write buffer flush for the
backpointer to be seen.

This shouldn't be a real issue in practice; the previous patch added a
new tracepoint so we'll be able to see more easily if it is.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/move.c

@@ -654,85 +654,6 @@ int bch2_move_data(struct bch_fs *c,
 	return ret;
 }
 
-void bch2_verify_bucket_evacuated(struct btree_trans *trans, struct bpos bucket, int gen)
-{
-	struct bch_fs *c = trans->c;
-	struct btree_iter iter;
-	struct bkey_s_c k;
-	struct printbuf buf = PRINTBUF;
-	struct bch_backpointer bp;
-	struct bpos bp_pos = POS_MIN;
-	unsigned nr_bps = 0;
-	int ret;
-
-	bch2_trans_begin(trans);
-
-	bch2_trans_iter_init(trans, &iter, BTREE_ID_alloc,
-			     bucket, BTREE_ITER_CACHED);
-again:
-	ret = lockrestart_do(trans,
-			bkey_err(k = bch2_btree_iter_peek_slot(&iter)));
-
-	if (!ret && k.k->type == KEY_TYPE_alloc_v4) {
-		struct bkey_s_c_alloc_v4 a = bkey_s_c_to_alloc_v4(k);
-
-		if (a.v->gen == gen &&
-		    a.v->dirty_sectors) {
-			if (a.v->data_type == BCH_DATA_btree) {
-				bch2_trans_unlock(trans);
-				if (bch2_btree_interior_updates_flush(c))
-					goto again;
-				goto failed_to_evacuate;
-			}
-		}
-	}
-
-	set_btree_iter_dontneed(&iter);
-	bch2_trans_iter_exit(trans, &iter);
-	return;
-failed_to_evacuate:
-	bch2_trans_iter_exit(trans, &iter);
-
-	if (test_bit(BCH_FS_EMERGENCY_RO, &c->flags))
-		return;
-
-	prt_printf(&buf, bch2_log_msg(c, "failed to evacuate bucket "));
-	bch2_bkey_val_to_text(&buf, c, k);
-
-	while (1) {
-		bch2_trans_begin(trans);
-
-		ret = bch2_get_next_backpointer(trans, bucket, gen,
-						&bp_pos, &bp,
-						BTREE_ITER_CACHED);
-		if (bch2_err_matches(ret, BCH_ERR_transaction_restart))
-			continue;
-		if (ret)
-			break;
-		if (bkey_eq(bp_pos, POS_MAX))
-			break;
-
-		k = bch2_backpointer_get_key(trans, &iter, bp_pos, bp, 0);
-		ret = bkey_err(k);
-		if (bch2_err_matches(ret, BCH_ERR_transaction_restart))
-			continue;
-		if (ret)
-			break;
-		if (!k.k)
-			continue;
-		prt_newline(&buf);
-		bch2_bkey_val_to_text(&buf, c, k);
-		bch2_trans_iter_exit(trans, &iter);
-
-		if (++nr_bps > 10)
-			break;
-		bp_pos = bpos_nosnap_successor(bp_pos);
-	}
-
-	bch2_print_string_as_lines(KERN_ERR, buf.buf);
-	printbuf_exit(&buf);
-}
-
 int __bch2_evacuate_bucket(struct btree_trans *trans,
 			   struct moving_context *ctxt,
 			   struct move_bucket_in_flight *bucket_in_flight,

fs/bcachefs/move.h

@@ -36,8 +36,6 @@ struct moving_context {
 	wait_queue_head_t	wait;
 };
 
-void bch2_verify_bucket_evacuated(struct btree_trans *, struct bpos, int);
-
 #define move_ctxt_wait_event(_ctxt, _trans, _cond)			\
 do {									\
 	bool cond_finished = false;					\

fs/bcachefs/movinggc.c

@@ -134,13 +134,6 @@ static void move_buckets_wait(struct btree_trans *trans,
 		if (atomic_read(&i->count))
 			break;
 
-		/*
-		 * moving_ctxt_exit calls bch2_write as it flushes pending
-		 * reads, which inits another btree_trans; this one must be
-		 * unlocked:
-		 */
-		bch2_verify_bucket_evacuated(trans, i->bucket.k.bucket, i->bucket.k.gen);
-
 		list->first = i->next;
 		if (!list->first)
 			list->last = NULL;