Re: [PATCH] vfs: fix vfs_rename_dir for FS_RENAME_DOES_D_MOVE filesystems

[Zach Brown <zach.brown@oracle.com>]

Miklos Szeredi wrote:
> On Fri, 11 Jul 2008, Sage Weil wrote:
>> However, vfs_rename_dir() doesn't properly account for filesystems with 
>> FS_RENAME_DOES_D_MOVE.  If new_dentry has a target inode attached, it 
>> unhashes the new_dentry prior to the rename() iop and rehashes it after, 
>> but doesn't account for the possibility that rename() may have swapped 
>> {old,new}_dentry.  For FS_RENAME_DOES_D_MOVE filesystems, it rehashes 
>> new_dentry (now the old renamed-from name, which d_move() expected to go 
>> away), such that a subsequent lookup will find it.
>>
>> To correct this, move vfs_rename_dir()'s call to d_move() _before_ the 
>> target inode mutex is dealt with.  Since d_move() will have been called 
>> for all filesystems at this point, there is no need to rehash new_dentry 
>> unless the rename failed.  (If the rename succeeded, old_dentry should 
>> already be rehashed in the new location.)
> 
> I think rehashing the new dentry is bogus, even on error.

So we'd just come back through lookup to repopulate the existing
destination name that vfs_rename_dir() unhashed before calling
->rename() in the case that the rename fails?  That seems gross, but
relatively harmless.

> So a better fix would be just to remove the rehashing completely.
> Does the below patch work for you?

It'd work for my case, yeah.

- z