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Commit 8ba97a15 authored by Jan Schmidt's avatar Jan Schmidt
Browse files

Btrfs: use btrfs_read_lock_root_node in get_old_root 



get_old_root could race with root node updates because we weren't locking
the node early enough. Use btrfs_read_lock_root_node to grab the root locked
in the very beginning and release the lock as soon as possible (just like
btrfs_search_slot does).

Signed-off-by: default avatarJan Schmidt <list.btrfs@jan-o-sch.net>
parent f617e2fd

fs/btrfs/ctree.c

+16 −4
Original line number Diff line number Diff line
@@ -1143,6 +1143,13 @@ tree_mod_log_rewind(struct btrfs_fs_info *fs_info, struct extent_buffer *eb, 
	return eb_rewin;

}



/*

 * get_old_root() rewinds the state of @root's root node to the given @time_seq

 * value. If there are no changes, the current root->root_node is returned. If

 * anything changed in between, there's a fresh buffer allocated on which the

 * rewind operations are done. In any case, the returned buffer is read locked.

 * Returns NULL on error (with no locks held).

 */

static inline struct extent_buffer *

get_old_root(struct btrfs_root *root, u64 time_seq)

{
@@ -1151,6 +1158,7 @@ get_old_root(struct btrfs_root *root, u64 time_seq) 
	struct tree_mod_root *old_root;

	u64 old_generation;



	eb = btrfs_read_lock_root_node(root);

	tm = __tree_mod_log_oldest_root(root->fs_info, root, time_seq);

	if (!tm)

		return root->node;
@@ -1173,15 +1181,21 @@ get_old_root(struct btrfs_root *root, u64 time_seq) 
		/* there's a root replace operation for the current root */

		eb = alloc_dummy_extent_buffer(tm->index << PAGE_CACHE_SHIFT,

					       root->nodesize);

	}

	btrfs_tree_read_unlock(root->node);

	free_extent_buffer(root->node);

	if (!eb)

		return NULL;

	btrfs_tree_read_lock(eb);

	if (old_root->logical != root->node->start) {

		btrfs_set_header_bytenr(eb, eb->start);

		btrfs_set_header_backref_rev(eb, BTRFS_MIXED_BACKREF_REV);

		btrfs_set_header_owner(eb, root->root_key.objectid);

	}

	if (!eb)

		return NULL;

	btrfs_set_header_level(eb, old_root->level);

	btrfs_set_header_generation(eb, old_generation);

	__tree_mod_log_rewind(eb, time_seq, tm);

	extent_buffer_get(eb);



	return eb;

}
@@ -2612,9 +2626,7 @@ int btrfs_search_old_slot(struct btrfs_root *root, struct btrfs_key *key, 


again:

	b = get_old_root(root, time_seq);

	extent_buffer_get(b);

	level = btrfs_header_level(b);

	btrfs_tree_read_lock(b);

	p->locks[level] = BTRFS_READ_LOCK;



	while (b) {