[RFC] libxfs: adding attribute fork frees xfs_inode ptr

[Mark Tinguely]

On 04/23/14 17:22, Dave Chinner wrote:
> On Wed, Apr 23, 2014 at 04:04:35PM -0500, Mark Tinguely wrote:
>> User space does not currently perform any attribute adding/deleting,
>> but if we do want to fix attributes or use them for parent inode
>> pointers, user space should support attributes.
>>
>> The adding an attribute fork is done in an embedded transaction
>> inside xfs_attr_set_int(). The xfs_trans_commit in xfs_bmap_add_attrfork()
>> will free the xfs_inode pointer causing xfs_attr_calc_size() in
>> xfs_attr_set_int() to fail.
>
> It shouldn't. xfs_bmap_add_attrfork() does:
>
> 	xfs_trans_ijoin(tp, ip, XFS_ILOCK_EXCL);
>
> which in the kernel code sets:
>
> 	iip->ili_lock_flags = lock_flags;
>
>
> The libxfs code doesn't do that, so when xfs_trans_commit() gets
> to inode_item_unlock():
>
>
>          if (!iip->ili_lock_flags)
>                  libxfs_iput(ip, 0);
>          else
>                  iip->ili_lock_flags = 0;
>
> It frees the inode rather than just returning it with the lock
> flags cleared.
>
> Note that libxfs still has libxfs_trans_ijoin_ref() which sets the
> lock flags, but this has been removed from the kernel code. IOWs,
> this is a libxfs/trans.c::xfs_trans_ijoin() bug, not something that
> needs fixing in the shared kernel/user libxfs code.
>
> Cheers,
>
> Dave.

nod. That is the correct thing to do.

Since the shared user/kernel code will no longer do a xfs_trans_ihold(), 
the libxfs_iput() should be factored out out of inode_item_unlock() and 
have the creator release the inode pointer when it is appropriate.

No one besides me is using this so it can go into the next release of 
xfs_progs.

--Mark.