On Tue, Oct 31, 2017 at 10:23:30PM +0200, Nikolay Borisov wrote:

On 30.10.2017 19:14, Liu Bo wrote:

quoted

If a file's DIR_ITEM key is invalid (due to memory errors) and gets
written to disk, a future lookup_path can end up with kernel panic due
to BUG_ON().

This gets rid of the BUG_ON(), meanwhile output the corrupted key and
return ENOENT if it's invalid.

Signed-off-by: Liu Bo <redacted>
---
The diff doesn't show the logic well, 'goto out_err' will return with
assigning 0 to location->objectid, and the caller already has a check
for (location->objectid == 0) to return -ENOENT.

 fs/btrfs/inode.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index d94e3f6..916cdc9 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c

@@ -5500,6 +5500,14 @@ static int btrfs_inode_by_name(struct inode *dir, struct dentry *dentry,
 		goto out_err;
 
 	btrfs_dir_item_key_to_cpu(path->nodes[0], di, location);
+	if (location->type != BTRFS_INODE_ITEM_KEY &&
+	    location->type != BTRFS_ROOT_ITEM_KEY) {
+		btrfs_warn(root->fs_info,
+	  "%s gets something invalid in DIR_ITEM (name %s, directory ino %llu, location(%llu %u %llu))",
+			   __func__, name, btrfs_ino(BTRFS_I(dir)),
+			   location->objectid, location->type, location->offset);
+		goto out_err;

If this situation happens it's possible that ret is still 0 so the error
handling in btrfs_lookup_dentry might not trigger. How about just
setting -EUCLEAN if we execute the if branch?

Thanks for the comment.  So it's not going to trigger the (ret < 0)
check, instead it tries to trigger the one following (ret < 0):

        if (location.objectid == 0)
                return ERR_PTR(-ENOENT);

which is consistent to the case when we didn't find the btrfs_dir_item
(di is NULL, returned by btrfs_lookup_dir_item()).

thanks,
-liubo

quoted

+	}
 out:
 	btrfs_free_path(path);
 	return ret;

@@ -5816,8 +5824,6 @@ struct inode *btrfs_lookup_dentry(struct inode *dir, struct dentry *dentry)
 		return inode;
 	}
 
-	BUG_ON(location.type != BTRFS_ROOT_ITEM_KEY);
-
 	index = srcu_read_lock(&fs_info->subvol_srcu);
 	ret = fixup_tree_root_location(fs_info, dir, dentry,
 				       &location, &sub_root);