[PATCH v3 5/6] btrfs: Change the lockdep class of struct inode's invalidate_lock

[Ioannis Angelakopoulos <iangelak@fb.com>]

Reinitialize the class of the lockdep map for
inode->mapping->invalidate_lock in load_free_space_cache() function in
fs/btrfs/free-space-cache.c This will prevent lockdep from producing false
positives related to execution paths that make use of free space inodes and
paths that make use of normal inodes.

Specifically, with this change lockdep will create separate lock
dependencies that include the invalidate_lock, in the case that free space
inodes are used and in the case that normal inodes are used.

Signed-off-by: Ioannis Angelakopoulos <iangelak@fb.com>
---
 fs/btrfs/free-space-cache.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index 996da650ecdc..a2b2329ae558 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -914,6 +914,8 @@ static int copy_free_space_cache(struct btrfs_block_group *block_group,
 	return ret;
 }
 
+static struct lock_class_key btrfs_free_space_inode_key;
+
 int load_free_space_cache(struct btrfs_block_group *block_group)
 {
 	struct btrfs_fs_info *fs_info = block_group->fs_info;
@@ -924,6 +926,7 @@ int load_free_space_cache(struct btrfs_block_group *block_group)
 	int ret = 0;
 	bool matched;
 	u64 used = block_group->used;
+	struct address_space *mapping;
 
 	/*
 	 * Because we could potentially discard our loaded free space, we want
@@ -983,6 +986,14 @@ int load_free_space_cache(struct btrfs_block_group *block_group)
 	}
 	spin_unlock(&block_group->lock);
 
+	/*
+	 * Reinitialize the class of the inode->mapping->invalidate_lock for free
+	 * space inodes to prevent false positives related to locks for normal
+	 * inodes.
+	 */
+	mapping = &inode->i_data;
+	lockdep_set_class(&mapping->invalidate_lock, &btrfs_free_space_inode_key);
+
 	ret = __load_free_space_cache(fs_info->tree_root, inode, &tmp_ctl,
 				      path, block_group->start);
 	btrfs_free_path(path);
-- 
2.30.2