Commit f651e948 authored Jun 15, 2020 by Zhiqiang Liu Committed by Greg Kroah-Hartman Jun 24, 2020

bcache: fix potential deadlock problem in btree_gc_coalesce



[ Upstream commit be23e837333a914df3f24bf0b32e87b0331ab8d1 ]

coccicheck reports:
  drivers/md//bcache/btree.c:1538:1-7: preceding lock on line 1417

In btree_gc_coalesce func, if the coalescing process fails, we will goto
to out_nocoalesce tag directly without releasing new_nodes[i]->write_lock.
Then, it will cause a deadlock when trying to acquire new_nodes[i]->
write_lock for freeing new_nodes[i] before return.

btree_gc_coalesce func details as follows:
	if alloc new_nodes[i] fails:
		goto out_nocoalesce;
	// obtain new_nodes[i]->write_lock
	mutex_lock(&new_nodes[i]->write_lock)
	// main coalescing process
	for (i = nodes - 1; i > 0; --i)
		[snipped]
		if coalescing process fails:
			// Here, directly goto out_nocoalesce
			 // tag will cause a deadlock
			goto out_nocoalesce;
		[snipped]
	// release new_nodes[i]->write_lock
	mutex_unlock(&new_nodes[i]->write_lock)
	// coalesing succ, return
	return;
out_nocoalesce:
	btree_node_free(new_nodes[i])	// free new_nodes[i]
	// obtain new_nodes[i]->write_lock
	mutex_lock(&new_nodes[i]->write_lock);
	// set flag for reuse
	clear_bit(BTREE_NODE_dirty, &ew_nodes[i]->flags);
	// release new_nodes[i]->write_lock
	mutex_unlock(&new_nodes[i]->write_lock);

To fix the problem, we add a new tag 'out_unlock_nocoalesce' for
releasing new_nodes[i]->write_lock before out_nocoalesce tag. If
coalescing process fails, we will go to out_unlock_nocoalesce tag
for releasing new_nodes[i]->write_lock before free new_nodes[i] in
out_nocoalesce tag.

(Coly Li helps to clean up commit log format.)

Fixes: 2a285686 ("bcache: btree locking rework")
Signed-off-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>

parent 889b69a9

drivers/md/bcache/btree.c

+6 −2

Original line number	Original line	Diff line number	Diff line
	@@ -1442,7 +1442,7 @@ static int btree_gc_coalesce(struct btree b, struct btree_op op,
	if (__set_blocks(n1, n1->keys + n2->keys,		if (__set_blocks(n1, n1->keys + n2->keys,
	block_bytes(b->c)) >		block_bytes(b->c)) >
	btree_blocks(new_nodes[i]))		btree_blocks(new_nodes[i]))
	goto out_nocoalesce;		goto out_unlock_nocoalesce;

	keys = n2->keys;		keys = n2->keys;
	/* Take the key of the node we're getting rid of */		/* Take the key of the node we're getting rid of */
	@@ -1471,7 +1471,7 @@ static int btree_gc_coalesce(struct btree b, struct btree_op op,

	if (__bch_keylist_realloc(&keylist,		if (__bch_keylist_realloc(&keylist,
	bkey_u64s(&new_nodes[i]->key)))		bkey_u64s(&new_nodes[i]->key)))
	goto out_nocoalesce;		goto out_unlock_nocoalesce;

	bch_btree_node_write(new_nodes[i], &cl);		bch_btree_node_write(new_nodes[i], &cl);
	bch_keylist_add(&keylist, &new_nodes[i]->key);		bch_keylist_add(&keylist, &new_nodes[i]->key);
	@@ -1517,6 +1517,10 @@ static int btree_gc_coalesce(struct btree b, struct btree_op op,
	/* Invalidated our iterator */		/* Invalidated our iterator */
	return -EINTR;		return -EINTR;

			out_unlock_nocoalesce:
			for (i = 0; i < nodes; i++)
			mutex_unlock(&new_nodes[i]->write_lock);

	out_nocoalesce:		out_nocoalesce:
	closure_sync(&cl);		closure_sync(&cl);