Re: [PATCH v16 11/11] xfs: Add delay ready attr set routines

[Brian Foster <bfoster@redhat.com>]

On Fri, Apr 02, 2021 at 02:01:20AM -0700, Allison Henderson wrote:
> 
> 
> On 4/1/21 9:57 AM, Brian Foster wrote:
> > On Thu, Mar 25, 2021 at 05:33:08PM -0700, Allison Henderson wrote:
> > > This patch modifies the attr set routines to be delay ready. This means
> > > they no longer roll or commit transactions, but instead return -EAGAIN
> > > to have the calling routine roll and refresh the transaction.  In this
> > > series, xfs_attr_set_args has become xfs_attr_set_iter, which uses a
> > > state machine like switch to keep track of where it was when EAGAIN was
> > > returned. See xfs_attr.h for a more detailed diagram of the states.
> > > 
> > > Two new helper functions have been added: xfs_attr_rmtval_find_space and
> > > xfs_attr_rmtval_set_blk.  They provide a subset of logic similar to
> > > xfs_attr_rmtval_set, but they store the current block in the delay attr
> > > context to allow the caller to roll the transaction between allocations.
> > > This helps to simplify and consolidate code used by
> > > xfs_attr_leaf_addname and xfs_attr_node_addname. xfs_attr_set_args has
> > > now become a simple loop to refresh the transaction until the operation
> > > is completed.  Lastly, xfs_attr_rmtval_remove is no longer used, and is
> > > removed.
> > > 
> > > Signed-off-by: Allison Henderson <allison.henderson@oracle.com>
> > > Reviewed-by: Chandan Babu R <chandanrlinux@gmail.com>
> > > Reviewed-by: Darrick J. Wong <djwong@kernel.org>
> > > ---
> > >   fs/xfs/libxfs/xfs_attr.c        | 446 ++++++++++++++++++++++++----------------
> > >   fs/xfs/libxfs/xfs_attr.h        | 241 +++++++++++++++++++++-
> > >   fs/xfs/libxfs/xfs_attr_remote.c | 100 ++++++---
> > >   fs/xfs/libxfs/xfs_attr_remote.h |   5 +-
> > >   fs/xfs/xfs_trace.h              |   1 -
> > >   5 files changed, 582 insertions(+), 211 deletions(-)
> > > 
> > > diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
> > > index 4a73691..6a86b62 100644
> > > --- a/fs/xfs/libxfs/xfs_attr.c
> > > +++ b/fs/xfs/libxfs/xfs_attr.c
> > ...
> > > @@ -246,29 +247,55 @@ xfs_attr_trans_roll(
> > >   	return error;
> > >   }
> > > +/*
> > > + * Set the attribute specified in @args.
> > > + */
> > > +int
> > > +xfs_attr_set_args(
> > > +	struct xfs_da_args		*args)
> > > +{
> > > +	struct xfs_buf			*leaf_bp = NULL;
> > > +	int				error = 0;
> > > +	struct xfs_delattr_context	dac = {
> > > +		.da_args	= args,
> > > +	};
> > > +
> > > +	do {
> > > +		error = xfs_attr_set_iter(&dac, &leaf_bp);
> > > +		if (error != -EAGAIN)
> > > +			break;
> > > +
> > > +		error = xfs_attr_trans_roll(&dac);
> > > +		if (error)
> > > +			return error;
> > > +	} while (true);
> > > +
> > > +	return error;
> > > +}
> > > +
> > >   STATIC int
> > >   xfs_attr_set_fmt(
> > > -	struct xfs_da_args	*args)
> > > +	struct xfs_delattr_context	*dac,
> > > +	struct xfs_buf			**leaf_bp)
> > >   {
> > > -	struct xfs_buf          *leaf_bp = NULL;
> > > -	struct xfs_inode	*dp = args->dp;
> > > -	int			error2, error = 0;
> > > +	struct xfs_da_args		*args = dac->da_args;
> > > +	struct xfs_inode		*dp = args->dp;
> > > +	int				error = 0;
> > >   	/*
> > >   	 * Try to add the attr to the attribute list in the inode.
> > >   	 */
> > >   	error = xfs_attr_try_sf_addname(dp, args);
> > > -	if (error != -ENOSPC) {
> > > -		error2 = xfs_trans_commit(args->trans);
> > > -		args->trans = NULL;
> > > -		return error ? error : error2;
> > > -	}
> > > +
> > > +	/* Should only be 0, -EEXIST or -ENOSPC */
> > > +	if (error != -ENOSPC)
> > > +		return error;
> > 
> > Ok, so it looks like the commit that goes away here is replaced by one
> > up the call stack.
> > 
> > >   	/*
> > >   	 * It won't fit in the shortform, transform to a leaf block.
> > >   	 * GROT: another possible req'mt for a double-split btree op.
> > >   	 */
> > > -	error = xfs_attr_shortform_to_leaf(args, &leaf_bp);
> > > +	error = xfs_attr_shortform_to_leaf(args, leaf_bp);
> > >   	if (error)
> > >   		return error;
> > > @@ -277,95 +304,139 @@ xfs_attr_set_fmt(
> > >   	 * concurrent AIL push cannot grab the half-baked leaf buffer
> > >   	 * and run into problems with the write verifier.
> > >   	 */
> > > -	xfs_trans_bhold(args->trans, leaf_bp);
> > > -	error = xfs_defer_finish(&args->trans);
> > > -	xfs_trans_bhold_release(args->trans, leaf_bp);
> > > -	if (error) {
> > > -		xfs_trans_brelse(args->trans, leaf_bp);
> > 
> > What about the xfs_trans_brelse() in the error case that seems to
> > disappear?
> Hmm, maybe we could add some handler in xfs_attr_set_args such that if the
> roll fails, we release the leaf_bp if it is not null?

I suspect we need it somewhere. I don't recall the details of this code
off the top of my head, but I remember it being tricky so we should
probably work to preserve current logic unless there's a clear reason to
do otherwise.

> > 
> > > -		return error;
> > > -	}
> > > +	xfs_trans_bhold(args->trans, *leaf_bp);
> > > +	/*
> > > +	 * We're still in XFS_DAS_UNINIT state here.  We've converted
> > > +	 * the attr fork to leaf format and will restart with the leaf
> > > +	 * add.
> > > +	 */
> > > +	dac->flags |= XFS_DAC_DEFER_FINISH;
> > >   	return -EAGAIN;
> > >   }
> > >   /*
> > >    * Set the attribute specified in @args.
> > > + * This routine is meant to function as a delayed operation, and may return
> > > + * -EAGAIN when the transaction needs to be rolled.  Calling functions will need
> > > + * to handle this, and recall the function until a successful error code is
> > > + * returned.
> > >    */
> > >   int
> > > -xfs_attr_set_args(
> > > -	struct xfs_da_args	*args)
> > > +xfs_attr_set_iter(
> > > +	struct xfs_delattr_context	*dac,
> > > +	struct xfs_buf			**leaf_bp)
> > >   {
> > > -	struct xfs_inode	*dp = args->dp;
> > > -	struct xfs_buf		*bp = NULL;
> > > -	struct xfs_da_state     *state = NULL;
> > > -	int			forkoff, error = 0;
> > > +	struct xfs_da_args              *args = dac->da_args;
> > > +	struct xfs_inode		*dp = args->dp;
> > > +	struct xfs_buf			*bp = NULL;
> > > +	struct xfs_da_state		*state = NULL;
> > > +	int				forkoff, error = 0;
> > > -	/*
> > > -	 * If the attribute list is already in leaf format, jump straight to
> > > -	 * leaf handling.  Otherwise, try to add the attribute to the shortform
> > > -	 * list; if there's no room then convert the list to leaf format and try
> > > -	 * again.
> > > -	 */
> > > -	if (xfs_attr_is_shortform(dp)) {
> > > -		error = xfs_attr_set_fmt(args);
> > > -		if (error != -EAGAIN)
> > > -			return error;
> > > -	}
> > > +	/* State machine switch */
> > > +	switch (dac->dela_state) {
> > > +	case XFS_DAS_UNINIT:
> > > +		if (xfs_attr_is_shortform(dp))
> > > +			return xfs_attr_set_fmt(dac, leaf_bp);
> > > -	if (xfs_bmap_one_block(dp, XFS_ATTR_FORK)) {
> > > -		error = xfs_attr_leaf_try_add(args, bp);
> > > -		if (error == -ENOSPC) {
> > > -			/*
> > > -			 * Promote the attribute list to the Btree format.
> > > -			 */
> > > -			error = xfs_attr3_leaf_to_node(args);
> > > +		/*
> > > +		 * After a shortform to leaf conversion, we need to hold the
> > > +		 * leaf and cycle out the transaction.  When we get back,
> > > +		 * we need to release the leaf to release the hold on the leaf
> > > +		 * buffer.
> > > +		 */
> > > +		if (*leaf_bp != NULL) {
> > > +			xfs_trans_bhold_release(args->trans, *leaf_bp);
> > > +			*leaf_bp = NULL;
> > > +		}
> > > +
> > > +		if (xfs_bmap_one_block(dp, XFS_ATTR_FORK)) {
> > > +			error = xfs_attr_leaf_try_add(args, *leaf_bp);
> > > +			if (error == -ENOSPC) {
> > > +				/*
> > > +				 * Promote the attribute list to the Btree
> > > +				 * format.
> > > +				 */
> > > +				error = xfs_attr3_leaf_to_node(args);
> > > +				if (error)
> > > +					return error;
> > > +
> > > +				/*
> > > +				 * Finish any deferred work items and roll the
> > > +				 * transaction once more.  The goal here is to
> > > +				 * call node_addname with the inode and
> > > +				 * transaction in the same state (inode locked
> > > +				 * and joined, transaction clean) no matter how
> > > +				 * we got to this step.
> > > +				 *
> > > +				 * At this point, we are still in
> > > +				 * XFS_DAS_UNINIT, but when we come back, we'll
> > > +				 * be a node, so we'll fall down into the node
> > > +				 * handling code below
> > > +				 */
> > > +				dac->flags |= XFS_DAC_DEFER_FINISH;
> > > +				return -EAGAIN;
> > > +			}
> > > +			else if (error)
> > 
> > Nit:			} else if (error)
> > 
> Sure, will fix
> 
> > > +				return error;
> > > +		}
> > > +		else {
> > 
> > Nit:		} else {
> will fix
> 
> > 
> > > +			error = xfs_attr_node_addname_find_attr(dac);
> > >   			if (error)
> > >   				return error;
> > > -			/*
> > > -			 * Finish any deferred work items and roll the transaction once
> > > -			 * more.  The goal here is to call node_addname with the inode
> > > -			 * and transaction in the same state (inode locked and joined,
> > > -			 * transaction clean) no matter how we got to this step.
> > > -			 */
> > > -			error = xfs_defer_finish(&args->trans);
> > > +			error = xfs_attr_node_addname(dac);
> > >   			if (error)
> > >   				return error;
> > 
> > Ok, so these couple of node calls get peeled out of the loop that
> > existed prior to this patch and xfs_attr_node_addname() returns -EAGAIN
> > to trigger reentry, if necessary.
> Right, that is the idea
> 
> > 
> > >   			/*
> > > -			 * Commit the current trans (including the inode) and
> > > -			 * start a new one.
> > > +			 * If addname was successful, and we dont need to alloc
> > > +			 * anymore blks, we're done.
> > >   			 */
> > > -			error = xfs_trans_roll_inode(&args->trans, dp);
> > > -			if (error)
> > > +			if (!args->rmtblkno && !args->rmtblkno2)
> > >   				return error;
> > 
> > Is this check new? What about clearing flags and whatnot?
> gosh, I remember putting this in, and now I'm struggling to remember the why
> that lead to it.  It's needed later in the set, but at this point its sort
> of an optimization.  In the xfs_attr_leaf_try_add, in the case of a rename,
> the blocks are saved for later processing.  If no blocks were saved, there's
> nothing to flip, so the idea is we can stop here. The extra go around isnt a
> big deal at this point, but it's a problem in delayed attrs, because you end
> up with an extra empty log entry.  in the extended set, we fail an assertion
> with out it:
> Assertion failed: !list_empty(&cil->xc_cil), file: fs/xfs/xfs_log_cil.c,
> line: 907
> 
> On my set up, we seem to get away without it at this point in the set, but
> it does have to go in eventually.  I think I must have worked through this
> bug at one time, and then placed the fix in this patch, as it seems to be a
> requirement for becoming "delay ready"
> 

Hmm, that seems like an odd failure to associate with this code. I guess
it's hard to grok because the context (i.e. delayed attrs) comes a bit
later. If possible, it might be wise to defer this hunk until where it's
necessary so the context/purpose is more clear on review (it also might
be helpful to explain the purpose in a bit more detail in the comment).

> 
> 
> > 
> > > -			goto node;
> > > -		}
> > > -		else if (error) {
> > > -			return error;
> > > +			dac->dela_state = XFS_DAS_FOUND_NBLK;
> > > +			return -EAGAIN;
> > >   		}
> > > -		/*
> > > -		 * Commit the transaction that added the attr name so that
> > > -		 * later routines can manage their own transactions.
> > > -		 */
> > > -		error = xfs_trans_roll_inode(&args->trans, dp);
> > > -		if (error)
> > > -			return error;
> > > +		dac->dela_state = XFS_DAS_FOUND_LBLK;
> > > +		return -EAGAIN;
> > 
> > Is there a reason the node branch sets the state in the branch but the
> > leaf branch falls out to here? I.e., could we not be consistent and have
> > 
> > 	if (one_block()) {
> > 		...
> > 		dac->dela_state = XFS_DAS_FOUND_LBLK;
> > 	} else {
> > 		...
> > 		dac->dela_state = XFS_DAS_FOUND_NBLK;
> > 	}
> > 	
> > 	return -EAGAIN;
> It's just sort of left over from its originally linear code flow that just
> sort of fell through in the the leaf logic. I think what you are proposing
> is logically analogous tho.  Does your example mean to add an extra if/else
> at the end here?  Or to tuck the return up into the the existing if/else?
> Both work, I am fine with either.
> 

Yes, the suggestion was intended to be logically equivalent. I think it
improves readability and is slightly less fragile to make the duplicated
code (i.e. return -EAGAIN) common and the state assignment as part of
the associated branch.

Brian

> > 
> > > +        case XFS_DAS_FOUND_LBLK:
> > >   		/*
> > >   		 * If there was an out-of-line value, allocate the blocks we
> > >   		 * identified for its storage and copy the value.  This is done
> > >   		 * after we create the attribute so that we don't overflow the
> > >   		 * maximum size of a transaction and/or hit a deadlock.
> > >   		 */
> > > -		if (args->rmtblkno > 0) {
> > > -			error = xfs_attr_rmtval_set(args);
> > > +
> > > +		/* Open coded xfs_attr_rmtval_set without trans handling */
> > > +		if ((dac->flags & XFS_DAC_LEAF_ADDNAME_INIT) == 0) {
> > > +			dac->flags |= XFS_DAC_LEAF_ADDNAME_INIT;
> > > +			if (args->rmtblkno > 0) {
> > > +				error = xfs_attr_rmtval_find_space(dac);
> > > +				if (error)
> > > +					return error;
> > > +			}
> > > +		}
> > > +
> > > +		/*
> > > +		 * Roll through the "value", allocating blocks on disk as
> > > +		 * required.
> > > +		 */
> > > +		if (dac->blkcnt > 0) {
> > > +			error = xfs_attr_rmtval_set_blk(dac);
> > >   			if (error)
> > >   				return error;
> > > +
> > > +			return -EAGAIN;
> > >   		}
> > > +		error = xfs_attr_rmtval_set_value(args);
> > > +		if (error)
> > > +			return error;
> > > +
> > >   		if (!(args->op_flags & XFS_DA_OP_RENAME)) {
> > >   			/*
> > >   			 * Added a "remote" value, just clear the incomplete
> > > @@ -394,22 +465,26 @@ xfs_attr_set_args(
> > >   		 * Commit the flag value change and start the next trans in
> > >   		 * series.
> > >   		 */
> > > -		error = xfs_trans_roll_inode(&args->trans, args->dp);
> > > -		if (error)
> > > -			return error;
> > > -
> > > +		dac->dela_state = XFS_DAS_FLIP_LFLAG;
> > > +		return -EAGAIN;
> > > +	case XFS_DAS_FLIP_LFLAG:
> > >   		/*
> > >   		 * Dismantle the "old" attribute/value pair by removing a
> > >   		 * "remote" value (if it exists).
> > >   		 */
> > >   		xfs_attr_restore_rmt_blk(args);
> > > -		if (args->rmtblkno) {
> > > -			error = xfs_attr_rmtval_invalidate(args);
> > > -			if (error)
> > > -				return error;
> > > +		error = xfs_attr_rmtval_invalidate(args);
> > > +		if (error)
> > > +			return error;
> > > +
> > > +		/* Set state in case xfs_attr_rmtval_remove returns -EAGAIN */
> > > +		dac->dela_state = XFS_DAS_RM_LBLK;
> > > -			error = xfs_attr_rmtval_remove(args);
> > > +		/* fallthrough */
> > > +	case XFS_DAS_RM_LBLK:
> > > +		if (args->rmtblkno) {
> > > +			error = __xfs_attr_rmtval_remove(dac);
> > >   			if (error)
> > >   				return error;
> > >   		}
> > 
> > This looks like a similar scenario as before where
> > xfs_attr_rmtval_remove() would have returned with a clean transaction
> > after the final unmap, but here __xfs_attr_rmtval_remove() just returns
> > 0 if done == 1. We probably need to roll one more time out of this
> > branch and land in a subsequent state..?
> I see, ok will add extra -EAGAIN here.
> 
> 
> > 
> > > @@ -434,91 +509,114 @@ xfs_attr_set_args(
> > >   			/* bp is gone due to xfs_da_shrink_inode */
> > >   		return error;
> > > -	}
> > > -node:
> > > +	case XFS_DAS_FOUND_NBLK:
> > > +		/*
> > > +		 * If there was an out-of-line value, allocate the blocks we
> > > +		 * identified for its storage and copy the value.  This is done
> > > +		 * after we create the attribute so that we don't overflow the
> > > +		 * maximum size of a transaction and/or hit a deadlock.
> > > +		 */
> > > +		if (args->rmtblkno > 0) {
> > > +			/*
> > > +			 * Open coded xfs_attr_rmtval_set without trans
> > > +			 * handling
> > > +			 */
> > > +			error = xfs_attr_rmtval_find_space(dac);
> > > +			if (error)
> > > +				return error;
> > > -	do {
> > > -		error = xfs_attr_node_addname_find_attr(args, &state);
> > > -		if (error)
> > > -			return error;
> > > -		error = xfs_attr_node_addname(args, state);
> > > -	} while (error == -EAGAIN);
> > > -	if (error)
> > > -		return error;
> > > +			/*
> > > +			 * Roll through the "value", allocating blocks on disk
> > > +			 * as required.  Set the state in case of -EAGAIN return
> > > +			 * code
> > > +			 */
> > > +			dac->dela_state = XFS_DAS_ALLOC_NODE;
> > > +		}
> > > -	/*
> > > -	 * Commit the leaf addition or btree split and start the next
> > > -	 * trans in the chain.
> > > -	 */
> > > -	error = xfs_trans_roll_inode(&args->trans, dp);
> > > -	if (error)
> > > -		goto out;
> > > +		/* fallthrough */
> > > +	case XFS_DAS_ALLOC_NODE:
> > > +		if (args->rmtblkno > 0) {
> > > +			if (dac->blkcnt > 0) {
> > > +				error = xfs_attr_rmtval_set_blk(dac);
> > > +				if (error)
> > > +					return error;
> > > -	/*
> > > -	 * If there was an out-of-line value, allocate the blocks we
> > > -	 * identified for its storage and copy the value.  This is done
> > > -	 * after we create the attribute so that we don't overflow the
> > > -	 * maximum size of a transaction and/or hit a deadlock.
> > > -	 */
> > > -	if (args->rmtblkno > 0) {
> > > -		error = xfs_attr_rmtval_set(args);
> > > -		if (error)
> > > -			return error;
> > > -	}
> > > +				return -EAGAIN;
> > > +			}
> > > +
> > > +			error = xfs_attr_rmtval_set_value(args);
> > > +			if (error)
> > > +				return error;
> > > +		}
> > > +
> > > +		if (!(args->op_flags & XFS_DA_OP_RENAME)) {
> > > +			/*
> > > +			 * Added a "remote" value, just clear the incomplete
> > > +			 * flag.
> > > +			 */
> > > +			if (args->rmtblkno > 0)
> > > +				error = xfs_attr3_leaf_clearflag(args);
> > > +			goto out;
> > > +		}
> > > -	if (!(args->op_flags & XFS_DA_OP_RENAME)) {
> > >   		/*
> > > -		 * Added a "remote" value, just clear the incomplete flag.
> > > +		 * If this is an atomic rename operation, we must "flip" the
> > > +		 * incomplete flags on the "new" and "old" attribute/value pairs
> > > +		 * so that one disappears and one appears atomically.  Then we
> > > +		 * must remove the "old" attribute/value pair.
> > > +		 *
> > > +		 * In a separate transaction, set the incomplete flag on the
> > > +		 * "old" attr and clear the incomplete flag on the "new" attr.
> > >   		 */
> > > -		if (args->rmtblkno > 0)
> > > -			error = xfs_attr3_leaf_clearflag(args);
> > > -		goto out;
> > > -	}
> > > -
> > > -	/*
> > > -	 * If this is an atomic rename operation, we must "flip" the incomplete
> > > -	 * flags on the "new" and "old" attribute/value pairs so that one
> > > -	 * disappears and one appears atomically.  Then we must remove the "old"
> > > -	 * attribute/value pair.
> > > -	 *
> > > -	 * In a separate transaction, set the incomplete flag on the "old" attr
> > > -	 * and clear the incomplete flag on the "new" attr.
> > > -	 */
> > > -	error = xfs_attr3_leaf_flipflags(args);
> > > -	if (error)
> > > -		goto out;
> > > -	/*
> > > -	 * Commit the flag value change and start the next trans in series
> > > -	 */
> > > -	error = xfs_trans_roll_inode(&args->trans, args->dp);
> > > -	if (error)
> > > -		goto out;
> > > +		error = xfs_attr3_leaf_flipflags(args);
> > > +		if (error)
> > > +			goto out;
> > > +		/*
> > > +		 * Commit the flag value change and start the next trans in
> > > +		 * series
> > > +		 */
> > > +		dac->dela_state = XFS_DAS_FLIP_NFLAG;
> > > +		return -EAGAIN;
> > > -	/*
> > > -	 * Dismantle the "old" attribute/value pair by removing a "remote" value
> > > -	 * (if it exists).
> > > -	 */
> > > -	xfs_attr_restore_rmt_blk(args);
> > > +	case XFS_DAS_FLIP_NFLAG:
> > > +		/*
> > > +		 * Dismantle the "old" attribute/value pair by removing a
> > > +		 * "remote" value (if it exists).
> > > +		 */
> > > +		xfs_attr_restore_rmt_blk(args);
> > > -	if (args->rmtblkno) {
> > >   		error = xfs_attr_rmtval_invalidate(args);
> > >   		if (error)
> > >   			return error;
> > > -		error = xfs_attr_rmtval_remove(args);
> > > -		if (error)
> > > -			return error;
> > > -	}
> > > +		/* Set state in case xfs_attr_rmtval_remove returns -EAGAIN */
> > > +		dac->dela_state = XFS_DAS_RM_NBLK;
> > > +
> > > +		/* fallthrough */
> > > +	case XFS_DAS_RM_NBLK:
> > > +		if (args->rmtblkno) {
> > > +			error = __xfs_attr_rmtval_remove(dac);
> > > +			if (error)
> > > +				return error;
> > > +		}
> > 
> > Similar thing here with __xfs_attr_rmtval_remove()..?
> Sure, will add one more -EAGAIN
> 
> > 
> > > +
> > > +		error = xfs_attr_node_addname_clear_incomplete(dac);
> > > -	error = xfs_attr_node_addname_clear_incomplete(args);
> > >   out:
> > > -	if (state)
> > > -		xfs_da_state_free(state);
> > > -	return error;
> > > +		if (state)
> > > +			xfs_da_state_free(state);
> > > +		return error;
> > 
> > Can we avoid this out label landing inside the switch statement? That
> > looks like a landmine. Even if we just duplicated an 'done_out' path
> > after the last return in the function, I think that would be preferable.
> Sure, can do, that seems like a simple thing to tack on
> 
> > 
> > All previous feedback aside, I think this patch now looks much more
> > digestable in general. Most of the state code is isolated to the _iter()
> > function and so it's much easier to follow along and compare against the
> > current code flow. I did still have some thoughts with regard to further
> > cleanups, possibly clearing up some the logic and/or tweaking the states
> > and whatnot, but I think this is at a point where it might be reasonable
> > to make such changes on top of this patch instead of continuing to make
> > significant changes to it. If I get a chance perhaps I'll take a closer
> > look at that once the remaining kinks are worked out..
> > 
> > Brian
> Ok, I will get these last bits updated here.  I still need to check into the
> issues Darrick is seeing on his set up, but it sounds like we've found an
> arrangement people like.  And yes, I think switching to cleanups on top is a
> good next step.  Thanks for the reviews!
> 
> Allison
> 
> > 
> > > +
> > > +	default:
> > > +		ASSERT(dac->dela_state != XFS_DAS_RM_SHRINK);
> > > +		break;
> > > +	}
> > > +	return error;
> > >   }
> > > +
> > >   /*
> > >    * Return EEXIST if attr is found, or ENOATTR if not
> > >    */
> > > @@ -984,18 +1082,18 @@ xfs_attr_node_hasname(
> > >   STATIC int
> > >   xfs_attr_node_addname_find_attr(
> > > -	struct xfs_da_args	*args,
> > > -	struct xfs_da_state     **state)
> > > +	struct xfs_delattr_context	*dac)
> > >   {
> > > -	int			retval;
> > > +	struct xfs_da_args		*args = dac->da_args;
> > > +	int				retval;
> > >   	/*
> > >   	 * Search to see if name already exists, and get back a pointer
> > >   	 * to where it should go.
> > >   	 */
> > > -	retval = xfs_attr_node_hasname(args, state);
> > > +	retval = xfs_attr_node_hasname(args, &dac->da_state);
> > >   	if (retval != -ENOATTR && retval != -EEXIST)
> > > -		goto error;
> > > +		return retval;
> > >   	if (retval == -ENOATTR && (args->attr_flags & XATTR_REPLACE))
> > >   		goto error;
> > > @@ -1021,8 +1119,8 @@ xfs_attr_node_addname_find_attr(
> > >   	return 0;
> > >   error:
> > > -	if (*state)
> > > -		xfs_da_state_free(*state);
> > > +	if (dac->da_state)
> > > +		xfs_da_state_free(dac->da_state);
> > >   	return retval;
> > >   }
> > > @@ -1035,20 +1133,24 @@ xfs_attr_node_addname_find_attr(
> > >    *
> > >    * "Remote" attribute values confuse the issue and atomic rename operations
> > >    * add a whole extra layer of confusion on top of that.
> > > + *
> > > + * This routine is meant to function as a delayed operation, and may return
> > > + * -EAGAIN when the transaction needs to be rolled.  Calling functions will need
> > > + * to handle this, and recall the function until a successful error code is
> > > + *returned.
> > >    */
> > >   STATIC int
> > >   xfs_attr_node_addname(
> > > -	struct xfs_da_args	*args,
> > > -	struct xfs_da_state	*state)
> > > +	struct xfs_delattr_context	*dac)
> > >   {
> > > -	struct xfs_da_state_blk	*blk;
> > > -	struct xfs_inode	*dp;
> > > -	int			error;
> > > +	struct xfs_da_args		*args = dac->da_args;
> > > +	struct xfs_da_state		*state = dac->da_state;
> > > +	struct xfs_da_state_blk		*blk;
> > > +	int				error;
> > >   	trace_xfs_attr_node_addname(args);
> > > -	dp = args->dp;
> > > -	blk = &state->path.blk[state->path.active-1];
> > > +	blk = &state->path.blk[ state->path.active-1 ];
> > >   	ASSERT(blk->magic == XFS_ATTR_LEAF_MAGIC);
> > >   	error = xfs_attr3_leaf_add(blk->bp, state->args);
> > > @@ -1064,18 +1166,15 @@ xfs_attr_node_addname(
> > >   			error = xfs_attr3_leaf_to_node(args);
> > >   			if (error)
> > >   				goto out;
> > > -			error = xfs_defer_finish(&args->trans);
> > > -			if (error)
> > > -				goto out;
> > >   			/*
> > > -			 * Commit the node conversion and start the next
> > > -			 * trans in the chain.
> > > +			 * Now that we have converted the leaf to a node, we can
> > > +			 * roll the transaction, and try xfs_attr3_leaf_add
> > > +			 * again on re-entry.  No need to set dela_state to do
> > > +			 * this. dela_state is still unset by this function at
> > > +			 * this point.
> > >   			 */
> > > -			error = xfs_trans_roll_inode(&args->trans, dp);
> > > -			if (error)
> > > -				goto out;
> > > -
> > > +			dac->flags |= XFS_DAC_DEFER_FINISH;
> > >   			return -EAGAIN;
> > >   		}
> > > @@ -1088,9 +1187,7 @@ xfs_attr_node_addname(
> > >   		error = xfs_da3_split(state);
> > >   		if (error)
> > >   			goto out;
> > > -		error = xfs_defer_finish(&args->trans);
> > > -		if (error)
> > > -			goto out;
> > > +		dac->flags |= XFS_DAC_DEFER_FINISH;
> > >   	} else {
> > >   		/*
> > >   		 * Addition succeeded, update Btree hashvals.
> > > @@ -1105,8 +1202,9 @@ xfs_attr_node_addname(
> > >   STATIC
> > >   int xfs_attr_node_addname_clear_incomplete(
> > > -	struct xfs_da_args		*args)
> > > +	struct xfs_delattr_context	*dac)
> > >   {
> > > +	struct xfs_da_args		*args = dac->da_args;
> > >   	struct xfs_da_state		*state = NULL;
> > >   	struct xfs_da_state_blk		*blk;
> > >   	int				retval = 0;
> > > diff --git a/fs/xfs/libxfs/xfs_attr.h b/fs/xfs/libxfs/xfs_attr.h
> > > index 92a6a50..4e4233d 100644
> > > --- a/fs/xfs/libxfs/xfs_attr.h
> > > +++ b/fs/xfs/libxfs/xfs_attr.h
> > > @@ -159,6 +159,233 @@ struct xfs_attr_list_context {
> > >    *              v
> > >    *            done
> > >    *
> > > + *
> > > + * Below is a state machine diagram for attr set operations.
> > > + *
> > > + * It seems the challenge with understanding this system comes from trying to
> > > + * absorb the state machine all at once, when really one should only be looking
> > > + * at it with in the context of a single function. Once a state sensitive
> > > + * function is called, the idea is that it "takes ownership" of the
> > > + * state machine. It isn't concerned with the states that may have belonged to
> > > + * it's calling parent. Only the states relevant to itself or any other
> > > + * subroutines there in. Once a calling function hands off the state machine to
> > > + * a subroutine, it needs to respect the simple rule that it doesn't "own" the
> > > + * state machine anymore, and it's the responsibility of that calling function
> > > + * to propagate the -EAGAIN back up the call stack. Upon reentry, it is
> > > + * committed to re-calling that subroutine until it returns something other than
> > > + * -EAGAIN. Once that subroutine signals completion (by returning anything other
> > > + * than -EAGAIN), the calling function can resume using the state machine.
> > > + *
> > > + *  xfs_attr_set_iter()
> > > + *              │
> > > + *              v
> > > + *   ┌─y─ has an attr fork?
> > > + *   │          |
> > > + *   │          n
> > > + *   │          |
> > > + *   │          V
> > > + *   │       add a fork
> > > + *   │          │
> > > + *   └──────────┤
> > > + *              │
> > > + *              V
> > > + *   ┌─y─ is shortform?
> > > + *   │          │
> > > + *   │          V
> > > + *   │   xfs_attr_set_fmt
> > > + *   │          |
> > > + *   │          V
> > > + *   │ xfs_attr_try_sf_addname
> > > + *   │          │
> > > + *   │          V
> > > + *   │      had enough ──y──> done
> > > + *   │        space?
> > > + *   n          │
> > > + *   │          n
> > > + *   │          │
> > > + *   │          V
> > > + *   │   transform to leaf
> > > + *   │          │
> > > + *   │          V
> > > + *   │   hold the leaf buffer
> > > + *   │          │
> > > + *   │          V
> > > + *   │     return -EAGAIN
> > > + *   │      Re-enter in
> > > + *   │       leaf form
> > > + *   │
> > > + *   └─> release leaf buffer
> > > + *          if needed
> > > + *              │
> > > + *              V
> > > + *   ┌───n── fork has
> > > + *   │      only 1 blk?
> > > + *   │          │
> > > + *   │          y
> > > + *   │          │
> > > + *   │          v
> > > + *   │ xfs_attr_leaf_try_add()
> > > + *   │          │
> > > + *   │          v
> > > + *   │      had enough ──────────────y───────────────???
> > > + *   │        space?                                 │
> > > + *   │          │                                    │
> > > + *   │          n                                    │
> > > + *   │          │                                    │
> > > + *   │          v                                    │
> > > + *   │    return -EAGAIN                             │
> > > + *   │      re-enter in                              │
> > > + *   │        node form                              │
> > > + *   │          │                                    │
> > > + *   └──────────┤                                    │
> > > + *              │                                    │
> > > + *              V                                    │
> > > + * xfs_attr_node_addname_find_attr                   │
> > > + *        determines if this                         │
> > > + *       is create or rename                         │
> > > + *     find space to store attr                      │
> > > + *              │                                    │
> > > + *              v                                    │
> > > + *     xfs_attr_node_addname                         │
> > > + *              │                                    │
> > > + *              v                                    │
> > > + *   fits in a node leaf? ────n─────???                │
> > > + *              │     ^             v                │
> > > + *              │     │        single leaf node?     │
> > > + *              │     │          │            │      │
> > > + *              y     │          y            n      │
> > > + *              │     │          │            │      │
> > > + *              v     │          v            v      │
> > > + *            update  │     grow the leaf  split if  │
> > > + *           hashvals └─── return -EAGAIN   needed   │
> > > + *              │          retry leaf add     │      │
> > > + *              │            on reentry       │      │
> > > + *              ├─────────────────────────────┘      │
> > > + *              │                                    │
> > > + *              v                                    │
> > > + *         need to alloc                             │
> > > + *   ┌─y── or flip flag?                             │
> > > + *   │          │                                    │
> > > + *   │          n                                    │
> > > + *   │          │                                    │
> > > + *   │          v                                    │
> > > + *   │         done                                  │
> > > + *   │                                               │
> > > + *   │                                               │
> > > + *   │         XFS_DAS_FOUND_LBLK <──────────────────┘
> > > + *   │                  │
> > > + *   │                  V
> > > + *   │        xfs_attr_leaf_addname()
> > > + *   │                  │
> > > + *   │                  v
> > > + *   │      ┌──first time through?
> > > + *   │      │          │
> > > + *   │      │          y
> > > + *   │      │          │
> > > + *   │      n          v
> > > + *   │      │    if we have rmt blks
> > > + *   │      │    find space for them
> > > + *   │      │          │
> > > + *   │      └──────────┤
> > > + *   │                 │
> > > + *   │                 v
> > > + *   │            still have
> > > + *   │      ┌─n─ blks to alloc? <──???
> > > + *   │      │          │           │
> > > + *   │      │          y           │
> > > + *   │      │          │           │
> > > + *   │      │          v           │
> > > + *   │      │     alloc one blk    │
> > > + *   │      │     return -EAGAIN ──┘
> > > + *   │      │    re-enter with one
> > > + *   │      │    less blk to alloc
> > > + *   │      │
> > > + *   │      │
> > > + *   │      └───> set the rmt
> > > + *   │               value
> > > + *   │                 │
> > > + *   │                 v
> > > + *   │               was this
> > > + *   │              a rename? ──n─???
> > > + *   │                 │          │
> > > + *   │                 y          │
> > > + *   │                 │          │
> > > + *   │                 v          │
> > > + *   │           flip incomplete  │
> > > + *   │               flag         │
> > > + *   │                 │          │
> > > + *   │                 v          │
> > > + *   │         XFS_DAS_FLIP_LFLAG │
> > > + *   │                 │          │
> > > + *   │                 v          │
> > > + *   │               remove       │
> > > + *   │        ┌───> old name      │
> > > + *   │        │        │          │
> > > + *   │ XFS_DAS_RM_LBLK │          │
> > > + *   │        ^        │          │
> > > + *   │        │        v          │
> > > + *   │        └──y── more to      │
> > > + *   │               remove       │
> > > + *   │                 │          │
> > > + *   │                 n          │
> > > + *   │                 │          │
> > > + *   │                 v          │
> > > + *   │                done <──────┘
> > > + *   │
> > > + *   └──────> XFS_DAS_FOUND_NBLK
> > > + *                     │
> > > + *                     v
> > > + *       ┌─────n──  need to
> > > + *       │        alloc blks?
> > > + *       │             │
> > > + *       │             y
> > > + *       │             │
> > > + *       │             v
> > > + *       │        find space
> > > + *       │             │
> > > + *       │             v
> > > + *       │  ┌─>XFS_DAS_ALLOC_NODE
> > > + *       │  │          │
> > > + *       │  │          v
> > > + *       │  │      alloc blk
> > > + *       │  │          │
> > > + *       │  │          v
> > > + *       │  └──y── need to alloc
> > > + *       │         more blocks?
> > > + *       │             │
> > > + *       │             n
> > > + *       │             │
> > > + *       │             v
> > > + *       │      set the rmt value
> > > + *       │             │
> > > + *       │             v
> > > + *       │          was this
> > > + *       └────────> a rename? ──n─???
> > > + *                     │          │
> > > + *                     y          │
> > > + *                     │          │
> > > + *                     v          │
> > > + *               flip incomplete  │
> > > + *                   flag         │
> > > + *                     │          │
> > > + *                     v          │
> > > + *             XFS_DAS_FLIP_NFLAG │
> > > + *                     │          │
> > > + *                     v          │
> > > + *                   remove       │
> > > + *        ┌────────> old name     │
> > > + *        │            │          │
> > > + *  XFS_DAS_RM_NBLK    │          │
> > > + *        ^            │          │
> > > + *        │            v          │
> > > + *        └──────y── more to      │
> > > + *                   remove       │
> > > + *                     │          │
> > > + *                     n          │
> > > + *                     │          │
> > > + *                     v          │
> > > + *                    done <──────┘
> > > + *
> > >    */
> > >   /*
> > > @@ -174,12 +401,20 @@ enum xfs_delattr_state {
> > >   	XFS_DAS_UNINIT		= 0,  /* No state has been set yet */
> > >   	XFS_DAS_RMTBLK,		      /* Removing remote blks */
> > >   	XFS_DAS_RM_SHRINK,	      /* We are shrinking the tree */
> > > +	XFS_DAS_FOUND_LBLK,	      /* We found leaf blk for attr */
> > > +	XFS_DAS_FOUND_NBLK,	      /* We found node blk for attr */
> > > +	XFS_DAS_FLIP_LFLAG,	      /* Flipped leaf INCOMPLETE attr flag */
> > > +	XFS_DAS_RM_LBLK,	      /* A rename is removing leaf blocks */
> > > +	XFS_DAS_ALLOC_NODE,	      /* We are allocating node blocks */
> > > +	XFS_DAS_FLIP_NFLAG,	      /* Flipped node INCOMPLETE attr flag */
> > > +	XFS_DAS_RM_NBLK,	      /* A rename is removing node blocks */
> > >   };
> > >   /*
> > >    * Defines for xfs_delattr_context.flags
> > >    */
> > >   #define XFS_DAC_DEFER_FINISH		0x01 /* finish the transaction */
> > > +#define XFS_DAC_LEAF_ADDNAME_INIT	0x02 /* xfs_attr_leaf_addname init*/
> > >   /*
> > >    * Context used for keeping track of delayed attribute operations
> > > @@ -187,6 +422,11 @@ enum xfs_delattr_state {
> > >   struct xfs_delattr_context {
> > >   	struct xfs_da_args      *da_args;
> > > +	/* Used in xfs_attr_rmtval_set_blk to roll through allocating blocks */
> > > +	struct xfs_bmbt_irec	map;
> > > +	xfs_dablk_t		lblkno;
> > > +	int			blkcnt;
> > > +
> > >   	/* Used in xfs_attr_node_removename to roll through removing blocks */
> > >   	struct xfs_da_state     *da_state;
> > > @@ -213,7 +453,6 @@ int xfs_attr_set_args(struct xfs_da_args *args);
> > >   int xfs_has_attr(struct xfs_da_args *args);
> > >   int xfs_attr_remove_args(struct xfs_da_args *args);
> > >   int xfs_attr_remove_iter(struct xfs_delattr_context *dac);
> > > -int xfs_attr_trans_roll(struct xfs_delattr_context *dac);
> > >   bool xfs_attr_namecheck(const void *name, size_t length);
> > >   void xfs_delattr_context_init(struct xfs_delattr_context *dac,
> > >   			      struct xfs_da_args *args);
> > > diff --git a/fs/xfs/libxfs/xfs_attr_remote.c b/fs/xfs/libxfs/xfs_attr_remote.c
> > > index 908521e7..fc71f10 100644
> > > --- a/fs/xfs/libxfs/xfs_attr_remote.c
> > > +++ b/fs/xfs/libxfs/xfs_attr_remote.c
> > > @@ -439,9 +439,9 @@ xfs_attr_rmtval_get(
> > >   /*
> > >    * Find a "hole" in the attribute address space large enough for us to drop the
> > > - * new attribute's value into
> > > + * new attributes value into
> > >    */
> > > -STATIC int
> > > +int
> > >   xfs_attr_rmt_find_hole(
> > >   	struct xfs_da_args	*args)
> > >   {
> > > @@ -468,7 +468,7 @@ xfs_attr_rmt_find_hole(
> > >   	return 0;
> > >   }
> > > -STATIC int
> > > +int
> > >   xfs_attr_rmtval_set_value(
> > >   	struct xfs_da_args	*args)
> > >   {
> > > @@ -628,6 +628,69 @@ xfs_attr_rmtval_set(
> > >   }
> > >   /*
> > > + * Find a hole for the attr and store it in the delayed attr context.  This
> > > + * initializes the context to roll through allocating an attr extent for a
> > > + * delayed attr operation
> > > + */
> > > +int
> > > +xfs_attr_rmtval_find_space(
> > > +	struct xfs_delattr_context	*dac)
> > > +{
> > > +	struct xfs_da_args		*args = dac->da_args;
> > > +	struct xfs_bmbt_irec		*map = &dac->map;
> > > +	int				error;
> > > +
> > > +	dac->lblkno = 0;
> > > +	dac->blkcnt = 0;
> > > +	args->rmtblkcnt = 0;
> > > +	args->rmtblkno = 0;
> > > +	memset(map, 0, sizeof(struct xfs_bmbt_irec));
> > > +
> > > +	error = xfs_attr_rmt_find_hole(args);
> > > +	if (error)
> > > +		return error;
> > > +
> > > +	dac->blkcnt = args->rmtblkcnt;
> > > +	dac->lblkno = args->rmtblkno;
> > > +
> > > +	return 0;
> > > +}
> > > +
> > > +/*
> > > + * Write one block of the value associated with an attribute into the
> > > + * out-of-line buffer that we have defined for it. This is similar to a subset
> > > + * of xfs_attr_rmtval_set, but records the current block to the delayed attr
> > > + * context, and leaves transaction handling to the caller.
> > > + */
> > > +int
> > > +xfs_attr_rmtval_set_blk(
> > > +	struct xfs_delattr_context	*dac)
> > > +{
> > > +	struct xfs_da_args		*args = dac->da_args;
> > > +	struct xfs_inode		*dp = args->dp;
> > > +	struct xfs_bmbt_irec		*map = &dac->map;
> > > +	int nmap;
> > > +	int error;
> > > +
> > > +	nmap = 1;
> > > +	error = xfs_bmapi_write(args->trans, dp, (xfs_fileoff_t)dac->lblkno,
> > > +				dac->blkcnt, XFS_BMAPI_ATTRFORK, args->total,
> > > +				map, &nmap);
> > > +	if (error)
> > > +		return error;
> > > +
> > > +	ASSERT(nmap == 1);
> > > +	ASSERT((map->br_startblock != DELAYSTARTBLOCK) &&
> > > +	       (map->br_startblock != HOLESTARTBLOCK));
> > > +
> > > +	/* roll attribute extent map forwards */
> > > +	dac->lblkno += map->br_blockcount;
> > > +	dac->blkcnt -= map->br_blockcount;
> > > +
> > > +	return 0;
> > > +}
> > > +
> > > +/*
> > >    * Remove the value associated with an attribute by deleting the
> > >    * out-of-line buffer that it is stored on.
> > >    */
> > > @@ -669,37 +732,6 @@ xfs_attr_rmtval_invalidate(
> > >   }
> > >   /*
> > > - * Remove the value associated with an attribute by deleting the
> > > - * out-of-line buffer that it is stored on.
> > > - */
> > > -int
> > > -xfs_attr_rmtval_remove(
> > > -	struct xfs_da_args		*args)
> > > -{
> > > -	int				error;
> > > -	struct xfs_delattr_context	dac  = {
> > > -		.da_args	= args,
> > > -	};
> > > -
> > > -	trace_xfs_attr_rmtval_remove(args);
> > > -
> > > -	/*
> > > -	 * Keep de-allocating extents until the remote-value region is gone.
> > > -	 */
> > > -	do {
> > > -		error = __xfs_attr_rmtval_remove(&dac);
> > > -		if (error != -EAGAIN)
> > > -			break;
> > > -
> > > -		error = xfs_attr_trans_roll(&dac);
> > > -		if (error)
> > > -			return error;
> > > -	} while (true);
> > > -
> > > -	return error;
> > > -}
> > > -
> > > -/*
> > >    * Remove the value associated with an attribute by deleting the out-of-line
> > >    * buffer that it is stored on. Returns -EAGAIN for the caller to refresh the
> > >    * transaction and re-call the function
> > > diff --git a/fs/xfs/libxfs/xfs_attr_remote.h b/fs/xfs/libxfs/xfs_attr_remote.h
> > > index 002fd30..8ad68d5 100644
> > > --- a/fs/xfs/libxfs/xfs_attr_remote.h
> > > +++ b/fs/xfs/libxfs/xfs_attr_remote.h
> > > @@ -10,9 +10,12 @@ int xfs_attr3_rmt_blocks(struct xfs_mount *mp, int attrlen);
> > >   int xfs_attr_rmtval_get(struct xfs_da_args *args);
> > >   int xfs_attr_rmtval_set(struct xfs_da_args *args);
> > > -int xfs_attr_rmtval_remove(struct xfs_da_args *args);
> > >   int xfs_attr_rmtval_stale(struct xfs_inode *ip, struct xfs_bmbt_irec *map,
> > >   		xfs_buf_flags_t incore_flags);
> > >   int xfs_attr_rmtval_invalidate(struct xfs_da_args *args);
> > >   int __xfs_attr_rmtval_remove(struct xfs_delattr_context *dac);
> > > +int xfs_attr_rmt_find_hole(struct xfs_da_args *args);
> > > +int xfs_attr_rmtval_set_value(struct xfs_da_args *args);
> > > +int xfs_attr_rmtval_set_blk(struct xfs_delattr_context *dac);
> > > +int xfs_attr_rmtval_find_space(struct xfs_delattr_context *dac);
> > >   #endif /* __XFS_ATTR_REMOTE_H__ */
> > > diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
> > > index e74bbb6..0c16d46 100644
> > > --- a/fs/xfs/xfs_trace.h
> > > +++ b/fs/xfs/xfs_trace.h
> > > @@ -1944,7 +1944,6 @@ DEFINE_ATTR_EVENT(xfs_attr_refillstate);
> > >   DEFINE_ATTR_EVENT(xfs_attr_rmtval_get);
> > >   DEFINE_ATTR_EVENT(xfs_attr_rmtval_set);
> > > -DEFINE_ATTR_EVENT(xfs_attr_rmtval_remove);
> > >   #define DEFINE_DA_EVENT(name) \
> > >   DEFINE_EVENT(xfs_da_class, name, \
> > > -- 
> > > 2.7.4
> > > 
> > 
>