commit b3e76af87441fc36eef3516d73ab2314e7b2d911
author Louis Rilling <Louis.Rilling@kerlabs.com> Mon Jun 16 19:01:01 2008 +0200
committer Mark Fasheh <mfasheh@suse.com> Mon Jul 14 13:57:16 2008 -0700
tree 36c6c6a21ac16b609302845a7dcb91749a972e4c
parent 107ed40bd070df5e4a0a012042c45c40963dc574

configfs: Fix deadlock with racing rmdir() and rename()

This patch fixes the deadlock between racing sys_rename() and configfs_rmdir().

The idea is to avoid locking i_mutexes of default groups in
configfs_detach_prep(), and rely instead on the new configfs_dirent_lock to
protect against configfs_dirent's linkage mutations. To ensure that an mkdir()
racing with rmdir() will not create new items in a to-be-removed default group,
we make configfs_new_dirent() check for the CONFIGFS_USET_DROPPING flag right
before linking the new dirent, and return error if the flag is set. This makes
racing mkdir()/symlink()/dir_open() fail in places where errors could already
happen, resp. in (attach_item()|attach_group())/create_link()/new_dirent().

configfs_depend() remains safe since it locks all the path from configfs root,
and is thus mutually exclusive with rmdir().

An advantage of this is that now detach_groups() unconditionnaly takes the
default groups i_mutex, which makes it more consistent with populate_groups().

Signed-off-by: Louis Rilling <Louis.Rilling@kerlabs.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>