[RFC] libxfs: adding attribute fork frees xfs_inode ptr

[RFC] libxfs: adding attribute fork frees xfs_inode ptr

[Mark Tinguely]

[-- Attachment #1: xfsprogs-fix-dp-release-when-adding-attr-fork.patch --]
[-- Type: text/plain, Size: 1373 bytes --]

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.

I don't see that we have any hold counts on the xfs_inode, so this is
a dirty FYI/RFC of a work around for this problem by calling xfs_iget()
to read back in the just freed inode.

---
 libxfs/xfs_attr.c |    4 ++++
 1 file changed, 4 insertions(+)

Index: b/libxfs/xfs_attr.c
===================================================================
--- a/libxfs/xfs_attr.c
+++ b/libxfs/xfs_attr.c
@@ -223,11 +223,15 @@ xfs_attr_set_int(
 	 * (inode must not be locked when we call this routine)
 	 */
 	if (XFS_IFORK_Q(dp) == 0) {
+		xfs_ino_t	ino = dp->i_ino;
 		int sf_size = sizeof(xfs_attr_sf_hdr_t) +
 			      XFS_ATTR_SF_ENTSIZE_BYNAME(name->len, valuelen);
 
 		if ((error = xfs_bmap_add_attrfork(dp, sf_size, rsvd)))
 			return(error);
+		error = libxfs_iget(mp, NULL, ino, 0, &dp, 0);
+		if (error)
+			return(error);
 	}
 
 	/*


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Re: [RFC] libxfs: adding attribute fork frees xfs_inode ptr

[Dave Chinner]

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.
-- 
Dave Chinner
david@fromorbit.com

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Re: [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.

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Re: [RFC] libxfs: adding attribute fork frees xfs_inode ptr

[Mark Tinguely]

On 04/24/14 12:11, Mark Tinguely wrote:
> On 04/23/14 17:22, Dave Chinner wrote:
>> On Wed, Apr 23, 2014 at 04:04:35PM -0500, Mark Tinguely wrote:

...

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.

PS. I may not have been very clear, the libxfs_trans_roll() and
     inode_item_done() also cause a premature libxfs_iput().
     Let me do more testing making any changes and target this for
     xfsprogs-3.2.1.

--Mark.

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Re: [RFC] libxfs: adding attribute fork frees xfs_inode ptr

[Christoph Hellwig]

On Thu, Apr 24, 2014 at 03:59:32PM -0500, Mark Tinguely wrote:
> PS. I may not have been very clear, the libxfs_trans_roll() and
>     inode_item_done() also cause a premature libxfs_iput().
>     Let me do more testing making any changes and target this for
>     xfsprogs-3.2.1.

You mean you've fixed the way we handle the attachement of inodes to
transaction in userspace to mirror what we do in kernelspace?  I'd love
to review this if you have patches as it's a somewhat of a pain point
to have these work so different in kernel and userspace.

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Re: [RFC] libxfs: adding attribute fork frees xfs_inode ptr

[Mark Tinguely]

On 04/25/14 00:40, Christoph Hellwig wrote:
> On Thu, Apr 24, 2014 at 03:59:32PM -0500, Mark Tinguely wrote:
>> PS. I may not have been very clear, the libxfs_trans_roll() and
>>      inode_item_done() also cause a premature libxfs_iput().
>>      Let me do more testing making any changes and target this for
>>      xfsprogs-3.2.1.
>
> You mean you've fixed the way we handle the attachement of inodes to
> transaction in userspace to mirror what we do in kernelspace?  I'd love
> to review this if you have patches as it's a somewhat of a pain point
> to have these work so different in kernel and userspace.
>

Not yet, I made the changes within the existing code so I can continue 
with my project. I agree, the user inode transaction code has to be 
synced with the kernel. I will start looking at it this weekend.

--Mark.

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