Re: fs/attr.c:notify_change locking warning.

[Christoph Hellwig <hch@xxxxxxxxxxxxx>]

On Wed, Oct 16, 2013 at 08:36:18AM +1100, Dave Chinner wrote:
> Sure, but file_remove_suid() doesn't actually modify any VFS inode
> structures until we process the flags and the modifications within
> ->setattr, which in XFS are all done under the XFS_ILOCK_EXCL via
> xfs_setattr_mode(). i.e. both the VFS and XFS inodes S*ID bits are
> removed only under XFS_ILOCK_EXCL....

It can set S_NOSEC after calling into ->setattr at least.

> Hence I see no point in adding extra serialisation via the i_mutex
> to this path when we can just do something like:
> 
>       killsuid = should_remove_suid(file->f_path.dentry);
>       if (killsuid) {
>               struct iattr    newattr;
> 
>               newattr.ia_valid = ATTR_FORCE | killsuid;
>               error = xfs_setattr_nonsize(ip, &newattr, 0);
>               if (error)
>                       return error;
>       }

We'd still need all the other magic in file_remove_suid, which I don't
actually quite undersdtand fully yet.