Re: [PATCH v16 10/11] xfs: Add delay ready attr remove routines

[Brian Foster <bfoster@redhat.com>]

On Fri, Apr 02, 2021 at 02:42:28AM -0700, Allison Henderson wrote:
> 
> 
> On 4/1/21 9:55 AM, Brian Foster wrote:
> > On Thu, Mar 25, 2021 at 05:33:07PM -0700, Allison Henderson wrote:
> > > This patch modifies the attr remove 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_remove_args is merged with
> > > xfs_attr_node_removename become a new function, xfs_attr_remove_iter.
> > > This new version uses a sort of state machine like switch to keep track
> > > of where it was when EAGAIN was returned. A new version of
> > > xfs_attr_remove_args consists of a simple loop to refresh the
> > > transaction until the operation is completed. A new XFS_DAC_DEFER_FINISH
> > > flag is used to finish the transaction where ever the existing code used
> > > to.
> > > 
> > > Calls to xfs_attr_rmtval_remove are replaced with the delay ready
> > > version __xfs_attr_rmtval_remove. We will rename
> > > __xfs_attr_rmtval_remove back to xfs_attr_rmtval_remove when we are
> > > done.
> > > 
> > > xfs_attr_rmtval_remove itself is still in use by the set routines (used
> > > during a rename).  For reasons of preserving existing function, we
> > > modify xfs_attr_rmtval_remove to call xfs_defer_finish when the flag is
> > > set.  Similar to how xfs_attr_remove_args does here.  Once we transition
> > > the set routines to be delay ready, xfs_attr_rmtval_remove is no longer
> > > used and will be removed.
> > > 
> > > This patch also adds a new struct xfs_delattr_context, which we will use
> > > to keep track of the current state of an attribute operation. The new
> > > xfs_delattr_state enum is used to track various operations that are in
> > > progress so that we know not to repeat them, and resume where we left
> > > off before EAGAIN was returned to cycle out the transaction. Other
> > > members take the place of local variables that need to retain their
> > > values across multiple function recalls.  See xfs_attr.h for a more
> > > detailed diagram of the states.
> > > 
> > > Signed-off-by: Allison Henderson <allison.henderson@oracle.com>
> > > ---
> > >   fs/xfs/libxfs/xfs_attr.c        | 206 +++++++++++++++++++++++++++-------------
> > >   fs/xfs/libxfs/xfs_attr.h        | 125 ++++++++++++++++++++++++
> > >   fs/xfs/libxfs/xfs_attr_leaf.c   |   2 +-
> > >   fs/xfs/libxfs/xfs_attr_remote.c |  48 ++++++----
> > >   fs/xfs/libxfs/xfs_attr_remote.h |   2 +-
> > >   fs/xfs/xfs_attr_inactive.c      |   2 +-
> > >   6 files changed, 297 insertions(+), 88 deletions(-)
> > > 
> > > diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
> > > index 41accd5..4a73691 100644
> > > --- a/fs/xfs/libxfs/xfs_attr.c
> > > +++ b/fs/xfs/libxfs/xfs_attr.c
> > ...
> > > @@ -221,6 +220,32 @@ xfs_attr_is_shortform(
> > >   		ip->i_afp->if_nextents == 0);
> > >   }
> > > +/*
> > > + * Checks to see if a delayed attribute transaction should be rolled.  If so,
> > > + * also checks for a defer finish.  Transaction is finished and rolled as
> > > + * needed, and returns true of false if the delayed operation should continue.
> > > + */
> > 
> > Outdated comment wrt to the return value.
> Ok, will drop last line here
> 
> > 
> > > +int
> > > +xfs_attr_trans_roll(
> > > +	struct xfs_delattr_context	*dac)
> > > +{
> > > +	struct xfs_da_args		*args = dac->da_args;
> > > +	int				error;
> > > +
> > > +	if (dac->flags & XFS_DAC_DEFER_FINISH) {
> > > +		/*
> > > +		 * The caller wants us to finish all the deferred ops so that we
> > > +		 * avoid pinning the log tail with a large number of deferred
> > > +		 * ops.
> > > +		 */
> > > +		dac->flags &= ~XFS_DAC_DEFER_FINISH;
> > > +		error = xfs_defer_finish(&args->trans);
> > > +	} else
> > > +		error = xfs_trans_roll_inode(&args->trans, args->dp);
> > > +
> > > +	return error;
> > > +}
> > > +
> > >   STATIC int
> > >   xfs_attr_set_fmt(
> > >   	struct xfs_da_args	*args)
> > ...
> > > @@ -1232,70 +1264,114 @@ xfs_attr_node_remove_cleanup(
> > >   }
> > >   /*
> > > - * Remove a name from a B-tree attribute list.
> > > + * Remove the attribute specified in @args.
> > >    *
> > >    * This will involve walking down the Btree, and may involve joining
> > >    * leaf nodes and even joining intermediate nodes up to and including
> > >    * the root node (a special case of an intermediate node).
> > > + *
> > > + * This routine is meant to function as either an in-line or 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_removename(
> > > -	struct xfs_da_args	*args)
> > > +int
> > > +xfs_attr_remove_iter(
> > > +	struct xfs_delattr_context	*dac)
> > >   {
> > > -	struct xfs_da_state	*state;
> > > -	int			retval, error;
> > > -	struct xfs_inode	*dp = args->dp;
> > > +	struct xfs_da_args		*args = dac->da_args;
> > > +	struct xfs_da_state		*state = dac->da_state;
> > > +	int				retval, error;
> > > +	struct xfs_inode		*dp = args->dp;
> > >   	trace_xfs_attr_node_removename(args);
> > > -	error = xfs_attr_node_removename_setup(args, &state);
> > > -	if (error)
> > > -		goto out;
> > > +	switch (dac->dela_state) {
> > > +	case XFS_DAS_UNINIT:
> > > +		if (!xfs_inode_hasattr(dp))
> > > +			return -ENOATTR;
> > > -	/*
> > > -	 * If there is an out-of-line value, de-allocate the blocks.
> > > -	 * This is done before we remove 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_remove(args);
> > > -		if (error)
> > > -			goto out;
> > > +		if (dp->i_afp->if_format == XFS_DINODE_FMT_LOCAL) {
> > > +			ASSERT(dp->i_afp->if_flags & XFS_IFINLINE);
> > > +			return xfs_attr_shortform_remove(args);
> > > +		}
> > > +
> > > +		if (xfs_bmap_one_block(dp, XFS_ATTR_FORK))
> > > +			return xfs_attr_leaf_removename(args);
> > > +
> > > +	/* fallthrough */
> > > +	case XFS_DAS_RMTBLK:
> > > +		dac->dela_state = XFS_DAS_RMTBLK;
> > > +
> > > +		if (!dac->da_state) {
> > > +			error = xfs_attr_node_removename_setup(dac);
> > > +			if (error)
> > > +				goto out;
> > 
> > Do we need the goto here if _removename_setup() frees state on error (or
> > is the latter change necessary)?
> I think we can safely return here.  Will update
> 
> > 
> > > +		}
> > > +		state = dac->da_state;
> > 
> > Also, can this fold into the above if (!da_state) branch? Or maybe the
> > whole setup branch pulled up into the UNINIT state? Not a big deal, but
> > it does look a little out of place in the RMTBLK state.
> Sure, it should be ok, there isnt any EAGAINs here, so it shouldnt make a
> difference
> 
> > 
> > >   		/*
> > > -		 * Refill the state structure with buffers, the prior calls
> > > -		 * released our buffers.
> > > +		 * If there is an out-of-line value, de-allocate the blocks.
> > > +		 * This is done before we remove the attribute so that we don't
> > > +		 * overflow the maximum size of a transaction and/or hit a
> > > +		 * deadlock.
> > >   		 */
> > > -		error = xfs_attr_refillstate(state);
> > > -		if (error)
> > > -			goto out;
> > > -	}
> > > -	retval = xfs_attr_node_remove_cleanup(args, state);
> > > +		if (args->rmtblkno > 0) {
> > > +			/*
> > > +			 * May return -EAGAIN. Remove blocks until
> > > +			 * args->rmtblkno == 0
> > > +			 */
> > > +			error = __xfs_attr_rmtval_remove(dac);
> > > +			if (error)
> > > +				break;
> > 
> > I feel that the difference between a break and goto out might confuse
> > some of the error handling. Right now, it looks like the exit path
> > handles either scenario, so we could presumably do something like the
> > following at the end of the function:
> > 
> > 	if (error != -EAGAIN && state)
> > 		xfs_da_state_free(state);
> > 	return error;
> > 
> > ... and just ditch the label. Alternatively we could retain the label above
> > the state check, but just use it consistently throughout the function.
> > 
> Either will work?  I think I'd prefer the gotos over the breaks though, I
> just think it reads easier.  The switch is sort of big, so I think the gotos
> make it a little more clear in that we're exiting the function without
> having to skim all the way to the bottom.
> 

Sounds reasonable to me as long as the error handling usage is
consistent. Thanks.

Brian

> > Other than those few nits, this one looks pretty good to me.
> Great, will update.  Thanks!
> 
> Allison
> 
> > 
> > Brian
> > 
> > > +
> > > +			/*
> > > +			 * Refill the state structure with buffers, the prior
> > > +			 * calls released our buffers.
> > > +			 */
> > > +			ASSERT(args->rmtblkno == 0);
> > > +			error = xfs_attr_refillstate(state);
> > > +			if (error)
> > > +				goto out;
> > > +
> > > +			dac->flags |= XFS_DAC_DEFER_FINISH;
> > > +			return -EAGAIN;
> > > +		}
> > > +
> > > +		retval = xfs_attr_node_remove_cleanup(args, state);
> > > -	/*
> > > -	 * Check to see if the tree needs to be collapsed.
> > > -	 */
> > > -	if (retval && (state->path.active > 1)) {
> > > -		error = xfs_da3_join(state);
> > > -		if (error)
> > > -			goto out;
> > > -		error = xfs_defer_finish(&args->trans);
> > > -		if (error)
> > > -			goto out;
> > >   		/*
> > > -		 * Commit the Btree join operation and start a new trans.
> > > +		 * Check to see if the tree needs to be collapsed. Set the flag
> > > +		 * to indicate that the calling function needs to move the
> > > +		 * shrink operation
> > >   		 */
> > > -		error = xfs_trans_roll_inode(&args->trans, dp);
> > > -		if (error)
> > > -			goto out;
> > > -	}
> > > +		if (retval && (state->path.active > 1)) {
> > > +			error = xfs_da3_join(state);
> > > +			if (error)
> > > +				goto out;
> > > -	/*
> > > -	 * If the result is small enough, push it all into the inode.
> > > -	 */
> > > -	if (xfs_bmap_one_block(dp, XFS_ATTR_FORK))
> > > -		error = xfs_attr_node_shrink(args, state);
> > > +			dac->flags |= XFS_DAC_DEFER_FINISH;
> > > +			dac->dela_state = XFS_DAS_RM_SHRINK;
> > > +			return -EAGAIN;
> > > +		}
> > > +
> > > +		/* fallthrough */
> > > +	case XFS_DAS_RM_SHRINK:
> > > +		/*
> > > +		 * If the result is small enough, push it all into the inode.
> > > +		 */
> > > +		if (xfs_bmap_one_block(dp, XFS_ATTR_FORK))
> > > +			error = xfs_attr_node_shrink(args, state);
> > > +
> > > +		break;
> > > +	default:
> > > +		ASSERT(0);
> > > +		error = -EINVAL;
> > > +		goto out;
> > > +	}
> > > +	if (error == -EAGAIN)
> > > +		return error;
> > >   out:
> > >   	if (state)
> > >   		xfs_da_state_free(state);
> > > diff --git a/fs/xfs/libxfs/xfs_attr.h b/fs/xfs/libxfs/xfs_attr.h
> > > index 3e97a93..92a6a50 100644
> > > --- a/fs/xfs/libxfs/xfs_attr.h
> > > +++ b/fs/xfs/libxfs/xfs_attr.h
> > > @@ -74,6 +74,127 @@ struct xfs_attr_list_context {
> > >   };
> > > +/*
> > > + * ========================================================================
> > > + * Structure used to pass context around among the delayed routines.
> > > + * ========================================================================
> > > + */
> > > +
> > > +/*
> > > + * Below is a state machine diagram for attr remove operations. The  XFS_DAS_*
> > > + * states indicate places where the function would return -EAGAIN, and then
> > > + * immediately resume from after being recalled by the calling function. States
> > > + * marked as a "subroutine state" indicate that they belong to a subroutine, and
> > > + * so the calling function needs to pass them back to that subroutine to allow
> > > + * it to finish where it left off. But they otherwise do not have a role in the
> > > + * calling function other than just passing through.
> > > + *
> > > + * xfs_attr_remove_iter()
> > > + *              │
> > > + *              v
> > > + *        have attr to remove? ──n──> done
> > > + *              │
> > > + *              y
> > > + *              │
> > > + *              v
> > > + *        are we short form? ──y──> xfs_attr_shortform_remove ──> done
> > > + *              │
> > > + *              n
> > > + *              │
> > > + *              V
> > > + *        are we leaf form? ──y──> xfs_attr_leaf_removename ──> done
> > > + *              │
> > > + *              n
> > > + *              │
> > > + *              V
> > > + *   ┌── need to setup state?
> > > + *   │          │
> > > + *   n          y
> > > + *   │          │
> > > + *   │          v
> > > + *   │ find attr and get state
> > > + *   │    attr has blks? ───n────???
> > > + *   │          │                v
> > > + *   │          │         find and invalidate
> > > + *   │          y         the blocks. mark
> > > + *   │          │         attr incomplete
> > > + *   │          ├────────────────┘
> > > + *   └──────────┤
> > > + *              │
> > > + *              v
> > > + *      Have blks to remove? ─────y────???
> > > + *              │       ^      remove the blks
> > > + *              │       │              │
> > > + *              │       │              v
> > > + *              │       │        refill the state
> > > + *              n       │              │
> > > + *              │       │              v
> > > + *              │       │         XFS_DAS_RMTBLK
> > > + *              │       └─────  re-enter with one
> > > + *              │               less blk to remove
> > > + *              │
> > > + *              v
> > > + *       remove leaf and
> > > + *       update hash with
> > > + *   xfs_attr_node_remove_cleanup
> > > + *              │
> > > + *              v
> > > + *           need to
> > > + *        shrink tree? ─n─???
> > > + *              │         │
> > > + *              y         │
> > > + *              │         │
> > > + *              v         │
> > > + *          join leaf     │
> > > + *              │         │
> > > + *              v         │
> > > + *      XFS_DAS_RM_SHRINK │
> > > + *              │         │
> > > + *              v         │
> > > + *       do the shrink    │
> > > + *              │         │
> > > + *              v         │
> > > + *          free state <──┘
> > > + *              │
> > > + *              v
> > > + *            done
> > > + *
> > > + */
> > > +
> > > +/*
> > > + * Enum values for xfs_delattr_context.da_state
> > > + *
> > > + * These values are used by delayed attribute operations to keep track  of where
> > > + * they were before they returned -EAGAIN.  A return code of -EAGAIN signals the
> > > + * calling function to roll the transaction, and then recall the subroutine to
> > > + * finish the operation.  The enum is then used by the subroutine to jump back
> > > + * to where it was and resume executing where it left off.
> > > + */
> > > +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 */
> > > +};
> > > +
> > > +/*
> > > + * Defines for xfs_delattr_context.flags
> > > + */
> > > +#define XFS_DAC_DEFER_FINISH		0x01 /* finish the transaction */
> > > +
> > > +/*
> > > + * Context used for keeping track of delayed attribute operations
> > > + */
> > > +struct xfs_delattr_context {
> > > +	struct xfs_da_args      *da_args;
> > > +
> > > +	/* Used in xfs_attr_node_removename to roll through removing blocks */
> > > +	struct xfs_da_state     *da_state;
> > > +
> > > +	/* Used to keep track of current state of delayed operation */
> > > +	unsigned int            flags;
> > > +	enum xfs_delattr_state  dela_state;
> > > +};
> > > +
> > >   /*========================================================================
> > >    * Function prototypes for the kernel.
> > >    *========================================================================*/
> > > @@ -91,6 +212,10 @@ int xfs_attr_set(struct xfs_da_args *args);
> > >   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);
> > >   #endif	/* __XFS_ATTR_H__ */
> > > diff --git a/fs/xfs/libxfs/xfs_attr_leaf.c b/fs/xfs/libxfs/xfs_attr_leaf.c
> > > index d6ef69a..3780141 100644
> > > --- a/fs/xfs/libxfs/xfs_attr_leaf.c
> > > +++ b/fs/xfs/libxfs/xfs_attr_leaf.c
> > > @@ -19,8 +19,8 @@
> > >   #include "xfs_bmap_btree.h"
> > >   #include "xfs_bmap.h"
> > >   #include "xfs_attr_sf.h"
> > > -#include "xfs_attr_remote.h"
> > >   #include "xfs_attr.h"
> > > +#include "xfs_attr_remote.h"
> > >   #include "xfs_attr_leaf.h"
> > >   #include "xfs_error.h"
> > >   #include "xfs_trace.h"
> > > diff --git a/fs/xfs/libxfs/xfs_attr_remote.c b/fs/xfs/libxfs/xfs_attr_remote.c
> > > index 48d8e9c..908521e7 100644
> > > --- a/fs/xfs/libxfs/xfs_attr_remote.c
> > > +++ b/fs/xfs/libxfs/xfs_attr_remote.c
> > > @@ -674,10 +674,12 @@ xfs_attr_rmtval_invalidate(
> > >    */
> > >   int
> > >   xfs_attr_rmtval_remove(
> > > -	struct xfs_da_args      *args)
> > > +	struct xfs_da_args		*args)
> > >   {
> > > -	int			error;
> > > -	int			retval;
> > > +	int				error;
> > > +	struct xfs_delattr_context	dac  = {
> > > +		.da_args	= args,
> > > +	};
> > >   	trace_xfs_attr_rmtval_remove(args);
> > > @@ -685,31 +687,29 @@ xfs_attr_rmtval_remove(
> > >   	 * Keep de-allocating extents until the remote-value region is gone.
> > >   	 */
> > >   	do {
> > > -		retval = __xfs_attr_rmtval_remove(args);
> > > -		if (retval && retval != -EAGAIN)
> > > -			return retval;
> > > +		error = __xfs_attr_rmtval_remove(&dac);
> > > +		if (error != -EAGAIN)
> > > +			break;
> > > -		/*
> > > -		 * Close out trans and start the next one in the chain.
> > > -		 */
> > > -		error = xfs_trans_roll_inode(&args->trans, args->dp);
> > > +		error = xfs_attr_trans_roll(&dac);
> > >   		if (error)
> > >   			return error;
> > > -	} while (retval == -EAGAIN);
> > > +	} while (true);
> > > -	return 0;
> > > +	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
> > > + * buffer that it is stored on. Returns -EAGAIN for the caller to refresh the
> > >    * transaction and re-call the function
> > >    */
> > >   int
> > >   __xfs_attr_rmtval_remove(
> > > -	struct xfs_da_args	*args)
> > > +	struct xfs_delattr_context	*dac)
> > >   {
> > > -	int			error, done;
> > > +	struct xfs_da_args		*args = dac->da_args;
> > > +	int				error, done;
> > >   	/*
> > >   	 * Unmap value blocks for this attr.
> > > @@ -719,12 +719,20 @@ __xfs_attr_rmtval_remove(
> > >   	if (error)
> > >   		return error;
> > > -	error = xfs_defer_finish(&args->trans);
> > > -	if (error)
> > > -		return error;
> > > -
> > > -	if (!done)
> > > +	/*
> > > +	 * We don't need an explicit state here to pick up where we left off. We
> > > +	 * can figure it out using the !done return code. Calling function only
> > > +	 * needs to keep recalling this routine until we indicate to stop by
> > > +	 * returning anything other than -EAGAIN. The actual value of
> > > +	 * attr->xattri_dela_state may be some value reminiscent of the calling
> > > +	 * function, but it's value is irrelevant with in the context of this
> > > +	 * function. Once we are done here, the next state is set as needed
> > > +	 * by the parent
> > > +	 */
> > > +	if (!done) {
> > > +		dac->flags |= XFS_DAC_DEFER_FINISH;
> > >   		return -EAGAIN;
> > > +	}
> > >   	return error;
> > >   }
> > > diff --git a/fs/xfs/libxfs/xfs_attr_remote.h b/fs/xfs/libxfs/xfs_attr_remote.h
> > > index 9eee615..002fd30 100644
> > > --- a/fs/xfs/libxfs/xfs_attr_remote.h
> > > +++ b/fs/xfs/libxfs/xfs_attr_remote.h
> > > @@ -14,5 +14,5 @@ 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_da_args *args);
> > > +int __xfs_attr_rmtval_remove(struct xfs_delattr_context *dac);
> > >   #endif /* __XFS_ATTR_REMOTE_H__ */
> > > diff --git a/fs/xfs/xfs_attr_inactive.c b/fs/xfs/xfs_attr_inactive.c
> > > index bfad669..aaa7e66 100644
> > > --- a/fs/xfs/xfs_attr_inactive.c
> > > +++ b/fs/xfs/xfs_attr_inactive.c
> > > @@ -15,10 +15,10 @@
> > >   #include "xfs_da_format.h"
> > >   #include "xfs_da_btree.h"
> > >   #include "xfs_inode.h"
> > > +#include "xfs_attr.h"
> > >   #include "xfs_attr_remote.h"
> > >   #include "xfs_trans.h"
> > >   #include "xfs_bmap.h"
> > > -#include "xfs_attr.h"
> > >   #include "xfs_attr_leaf.h"
> > >   #include "xfs_quota.h"
> > >   #include "xfs_dir2.h"
> > > -- 
> > > 2.7.4
> > > 
> > 
>