From a879719b8c90e15c9e7fa7266d5e3c0ca962f9df Mon Sep 17 00:00:00 2001 From: Filipe Manana Date: Thu, 31 Dec 2015 18:07:59 +0000 Subject: [PATCH] Btrfs: send, don't BUG_ON() when an empty symlink is found When a symlink is successfully created it always has an inline extent containing the source path. However if an error happens when creating the symlink, we can leave in the subvolume's tree a symlink inode without any such inline extent item - this happens if after btrfs_symlink() calls btrfs_end_transaction() and before it calls the inode eviction handler (through the final iput() call), the transaction gets committed and a crash happens before the eviction handler gets called, or if a snapshot of the subvolume is made before the eviction handler gets called. Sadly we can't just avoid this by making btrfs_symlink() call btrfs_end_transaction() after it calls the eviction handler, because the later can commit the current transaction before it removes any items from the subvolume tree (if it encounters ENOSPC errors while reserving space for removing all the items). So make send fail more gracefully, with an -EIO error, and print a message to dmesg/syslog informing that there's an empty symlink inode, so that the user can delete the empty symlink or do something else about it. Reported-by: Stephen R. van den Berg Signed-off-by: Filipe Manana --- fs/btrfs/send.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c index 355a458cba1a..63a6152be04b 100644 --- a/fs/btrfs/send.c +++ b/fs/btrfs/send.c @@ -1469,7 +1469,21 @@ static int read_symlink(struct btrfs_root *root, ret = btrfs_search_slot(NULL, root, &key, path, 0, 0); if (ret < 0) goto out; - BUG_ON(ret); + if (ret) { + /* + * An empty symlink inode. Can happen in rare error paths when + * creating a symlink (transaction committed before the inode + * eviction handler removed the symlink inode items and a crash + * happened in between or the subvol was snapshoted in between). + * Print an informative message to dmesg/syslog so that the user + * can delete the symlink. + */ + btrfs_err(root->fs_info, + "Found empty symlink inode %llu at root %llu", + ino, root->root_key.objectid); + ret = -EIO; + goto out; + } ei = btrfs_item_ptr(path->nodes[0], path->slots[0], struct btrfs_file_extent_item); -- 2.20.1