Commit b301105b authored by Kent Overstreet's avatar Kent Overstreet Committed by Kent Overstreet
Browse files

bcachefs: normalize_read_intent_locks 



This is a new approach to avoiding the self deadlock we'd get if we
tried to take a write lock on a node while holding a read lock - we
simply upgrade the readers to intent.

Signed-off-by: default avatarKent Overstreet <kent.overstreet@gmail.com>
parent 8ee0134e

fs/bcachefs/btree_update_leaf.c

+61 −12
Original line number Diff line number Diff line
@@ -48,14 +48,12 @@ static inline bool same_leaf_as_next(struct btree_trans *trans, 
		insert_l(&i[0])->b == insert_l(&i[1])->b;

}



inline void bch2_btree_node_lock_for_insert(struct btree_trans *trans,

static inline void bch2_btree_node_prep_for_write(struct btree_trans *trans,

						  struct btree_path *path,

						  struct btree *b)

{

	struct bch_fs *c = trans->c;



	bch2_btree_node_lock_write(trans, path, b);



	if (path->cached)

		return;
@@ -71,6 +69,14 @@ inline void bch2_btree_node_lock_for_insert(struct btree_trans *trans, 
		bch2_btree_init_next(trans, b);

}



void bch2_btree_node_lock_for_insert(struct btree_trans *trans,

				     struct btree_path *path,

				     struct btree *b)

{

	bch2_btree_node_lock_write(trans, path, b);

	bch2_btree_node_prep_for_write(trans, path, b);

}



/* Inserting into a given leaf node (last stage of insert): */



/* Handle overwrites and do insert, for non extents: */
@@ -495,6 +501,50 @@ bch2_trans_commit_write_locked(struct btree_trans *trans, 
	return ret;

}



static inline void upgrade_readers(struct btree_trans *trans, struct btree_path *path)

{

	struct btree *b = path_l(path)->b;



	do {

		if (path->nodes_locked &&

		    path->nodes_locked != path->nodes_intent_locked)

			BUG_ON(!bch2_btree_path_upgrade(trans, path, path->level + 1));

	} while ((path = prev_btree_path(trans, path)) &&

		 path_l(path)->b == b);

}



/*

 * Check for nodes that we have both read and intent locks on, and upgrade the

 * readers to intent:

 */

static inline void normalize_read_intent_locks(struct btree_trans *trans)

{

	struct btree_path *path;

	unsigned i, nr_read = 0, nr_intent = 0;



	trans_for_each_path_inorder(trans, path, i) {

		struct btree_path *next = i + 1 < trans->nr_sorted

			? trans->paths + trans->sorted[i + 1]

			: NULL;



		if (path->nodes_locked) {

			if (path->nodes_intent_locked)

				nr_intent++;

			else

				nr_read++;

		}



		if (!next || path_l(path)->b != path_l(next)->b) {

			if (nr_read && nr_intent)

				upgrade_readers(trans, path);



			nr_read = nr_intent = 0;

		}

	}



	bch2_trans_verify_locks(trans);

}



/*

 * Get journal reservation, take write locks, and attempt to do btree update(s):

 */
@@ -538,9 +588,6 @@ static inline int do_bch2_trans_commit(struct btree_trans *trans, 
		}

	}



	trans_for_each_update(trans, i)

		BUG_ON(!btree_node_intent_locked(i->path, i->level));



	ret = bch2_journal_preres_get(&c->journal,

			&trans->journal_preres, trans->journal_preres_u64s,

			JOURNAL_RES_GET_NONBLOCK|
@@ -586,12 +633,14 @@ static inline int do_bch2_trans_commit(struct btree_trans *trans, 
		}

		btree_insert_entry_checks(trans, i);

	}

	bch2_trans_verify_locks(trans);



	normalize_read_intent_locks(trans);



	trans_for_each_update(trans, i)

		if (!same_leaf_as_prev(trans, i))

			bch2_btree_node_lock_for_insert(trans, i->path,

					insert_l(i)->b);

		if (!same_leaf_as_prev(trans, i)) {

			btree_node_lock_type(c, insert_l(i)->b, SIX_LOCK_write);

			bch2_btree_node_prep_for_write(trans, i->path, insert_l(i)->b);

		}



	ret = bch2_trans_commit_write_locked(trans, stopped_at, trace_ip);