Commit 5cd57b2c authored by Chris Mason's avatar Chris Mason
Browse files

Btrfs: Add a skip_locking parameter to struct path, and make various funcs honor it 



Allocations may need to read in block groups from the extent allocation tree,
which will require a tree search and take locks on the extent allocation
tree.  But, those locks might already be held in other places, leading
to deadlocks.

Since the alloc_mutex serializes everything right now, it is safe to
skip the btree locking while caching block groups.  A better fix will be
to either create a recursive lock or find a way to back off existing
locks while caching block groups.

Signed-off-by: default avatarChris Mason <chris.mason@oracle.com>
parent 168fd7d2

fs/btrfs/ctree.c

+18 −14
Original line number Diff line number Diff line
@@ -64,6 +64,7 @@ void btrfs_release_path(struct btrfs_root *root, struct btrfs_path *p) 
{

	int i;

	int keep = p->keep_locks;

	int skip = p->skip_locking;



	for (i = 0; i < BTRFS_MAX_LEVEL; i++) {

		if (!p->nodes[i])
@@ -76,6 +77,7 @@ void btrfs_release_path(struct btrfs_root *root, struct btrfs_path *p) 
	}

	memset(p, 0, sizeof(*p));

	p->keep_locks = keep;

	p->skip_locking = skip;

}



struct extent_buffer *btrfs_root_node(struct btrfs_root *root)
@@ -1262,6 +1264,9 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root 
	if (ins_len < 0)

		lowest_unlock = 2;

again:

	if (p->skip_locking)

		b = btrfs_root_node(root);

	else

		b = btrfs_lock_root_node(root);



	while (b) {
@@ -1282,6 +1287,7 @@ again: 
			WARN_ON(1);

		level = btrfs_header_level(b);

		p->nodes[level] = b;

		if (!p->skip_locking)

			p->locks[level] = 1;

		ret = check_block(root, p, level);

		if (ret)
@@ -1349,6 +1355,7 @@ again: 
					b = read_node_slot(root, b, slot);

				}

			}

			if (!p->skip_locking)

				btrfs_tree_lock(b);

			unlock_up(p, level, lowest_unlock);

		} else {
@@ -1392,13 +1399,6 @@ static int fixup_low_keys(struct btrfs_trans_handle *trans, 
			break;

		t = path->nodes[i];

		btrfs_set_node_key(t, key, tslot);

		if (!btrfs_tree_locked(path->nodes[i])) {

			int ii;

printk("fixup without lock on level %d\n", btrfs_header_level(path->nodes[i]));

			for (ii = 0; ii < BTRFS_MAX_LEVEL; ii++) {

printk("level %d slot %d\n", ii, path->slots[ii]);

			}

		}

		btrfs_mark_buffer_dirty(path->nodes[i]);

		if (tslot != 0)

			break;
@@ -3033,8 +3033,10 @@ int btrfs_next_leaf(struct btrfs_root *root, struct btrfs_path *path) 
			reada_for_search(root, path, level, slot, 0);



		next = read_node_slot(root, c, slot);

		if (!path->skip_locking) {

			WARN_ON(!btrfs_tree_locked(c));

			btrfs_tree_lock(next);

		}

		break;

	}

	path->slots[level] = slot;
@@ -3052,9 +3054,11 @@ int btrfs_next_leaf(struct btrfs_root *root, struct btrfs_path *path) 
		if (level == 1 && path->locks[1] && path->reada)

			reada_for_search(root, path, level, slot, 0);

		next = read_node_slot(root, next, 0);

		if (!path->skip_locking) {

			WARN_ON(!btrfs_tree_locked(path->nodes[level]));

			btrfs_tree_lock(next);

		}

	}

done:

	unlock_up(path, 0, 1);

	return 0;

fs/btrfs/ctree.h

+1 −0
Original line number Diff line number Diff line
@@ -335,6 +335,7 @@ struct btrfs_path { 
	int reada;

	/* keep some upper locks as we walk down */

	int keep_locks;

	int skip_locking;

	int lowest_level;

};

fs/btrfs/extent-tree.c

+6 −0
Original line number Diff line number Diff line
@@ -88,6 +88,12 @@ static int cache_block_group(struct btrfs_root *root, 
		return -ENOMEM;



	path->reada = 2;

	/*

	 * we get into deadlocks with paths held by callers of this function.

	 * since the alloc_mutex is protecting things right now, just

	 * skip the locking here

	 */

	path->skip_locking = 1;

	first_free = block_group->key.objectid;

	key.objectid = block_group->key.objectid;

	key.offset = 0;

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