On Tue, Apr 17, 2012 at 07:28:26PM +0100, Al Viro wrote: > On Tue, Apr 17, 2012 at 07:01:29PM +0100, Al Viro wrote: > > > It isn't. Hell knows - I wonder if taking s_vfs_rename_mutex in all cases > > in lock_rename() would be the right thing to do; it would remove the > > problem, but might cost us too much contention... > > Actually, it's even worse. ext4_move_extents() locks a _pair_ of > ->i_mutex (having checked that both are non-directories first). In > i_ino order. So the only plausible ordering would be > * directories by tree order (with s_vfs_rename_mutex held to > stabilize the tree topology) > * non-directories after all directories, ordered in some consistent > way. Which would have to be by inumber if we want to leave ext4 code > as-is. > > Bruce: for now I'm dropping that patch. We _might_ take ext4 > mutex_inode_double_lock() into fs/namei.c and have it used by > vfs_rename_other(), but I'm not convinced that this is the right > thing to do. Is there any other sane way to deal with nfsd problem? > i_mutex is already used for more things than I'd like... I don't want to give out a delegation while a rename, link, unlink, or setattr of an inode is in progress. All but rename are covered by the i_mutex. I'm happy just failing the delegation in case of conflict. Maybe instead I could continue using the i_mutex but handle rename some other way; e.g. in delegation code: if (!mutex_trylock(inode->i_mutex)) return -EAGAIN; if (atomic_read(inode->i_renames_in_progress)) return -EAGAIN; and add an atomic_inc(inode->i_renames_in_progress); atomic_dec(inode->i_renames_in_progress); pair around rename. Or I could increment that counter for all the conflicting operations and rely on it instead of the i_mutex. I was trying to avoid adding something like that (an inc, a dec, another error path) to every operation. And hoping to avoid adding another field to struct inode. Oh well. --b. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
