Re: [PATCH v14 04/15] xfs: Add delay ready attr remove routines

[Chandan Babu R <chandanrlinux@gmail.com>]

On Fri, 18 Dec 2020 00:29:06 -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 has become xfs_attr_remove_iter, which
> uses a sort of state machine like switch to keep track of where it was
> when EAGAIN was returned. xfs_attr_node_removename has also been
> modified to use the switch, and 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        | 218 +++++++++++++++++++++++++++++-----------
>  fs/xfs/libxfs/xfs_attr.h        | 100 ++++++++++++++++++
>  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, 288 insertions(+), 84 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
> index 1969b88..b6330f9 100644
> --- a/fs/xfs/libxfs/xfs_attr.c
> +++ b/fs/xfs/libxfs/xfs_attr.c
> @@ -53,7 +53,7 @@ STATIC int xfs_attr_leaf_hasname(struct xfs_da_args *args, struct xfs_buf **bp);
>   */
>  STATIC int xfs_attr_node_get(xfs_da_args_t *args);
>  STATIC int xfs_attr_node_addname(xfs_da_args_t *args);
> -STATIC int xfs_attr_node_removename(xfs_da_args_t *args);
> +STATIC int xfs_attr_node_removename_iter(struct xfs_delattr_context *dac);
>  STATIC int xfs_attr_node_hasname(xfs_da_args_t *args,
>  				 struct xfs_da_state **state);
>  STATIC int xfs_attr_fillstate(xfs_da_state_t *state);
> @@ -264,6 +264,34 @@ xfs_attr_set_shortform(
>  }
>  
>  /*
> + * 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.
> + */
> +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);
> +		if (error)
> +			return error;
> +	} else
> +		error = xfs_trans_roll_inode(&args->trans, args->dp);
> +
> +	return error;
> +}
> +
> +/*
>   * Set the attribute specified in @args.
>   */
>  int
> @@ -364,23 +392,58 @@ xfs_has_attr(
>   */
>  int
>  xfs_attr_remove_args(
> -	struct xfs_da_args      *args)
> +	struct xfs_da_args	*args)
>  {
> -	struct xfs_inode	*dp = args->dp;
> -	int			error;
> +	int				error;
> +	struct xfs_delattr_context	dac = {
> +		.da_args	= args,
> +	};
> +
> +	do {
> +		error = xfs_attr_remove_iter(&dac);
> +		if (error != -EAGAIN)
> +			break;
> +
> +		error = xfs_attr_trans_roll(&dac);
> +		if (error)
> +			return error;
> +
> +	} while (true);
> +
> +	return error;
> +}
>  
> -	if (!xfs_inode_hasattr(dp)) {
> -		error = -ENOATTR;
> -	} else if (dp->i_afp->if_format == XFS_DINODE_FMT_LOCAL) {
> +/*
> + * Remove the attribute specified in @args.
> + *
> + * This function may return -EAGAIN to signal that the transaction needs to be
> + * rolled.  Callers should continue calling this function until they receive a
> + * return value other than -EAGAIN.
> + */
> +int
> +xfs_attr_remove_iter(
> +	struct xfs_delattr_context	*dac)
> +{
> +	struct xfs_da_args		*args = dac->da_args;
> +	struct xfs_inode		*dp = args->dp;
> +
> +	/* If we are shrinking a node, resume shrink */
> +	if (dac->dela_state == XFS_DAS_RM_SHRINK)
> +		goto node;
> +
> +	if (!xfs_inode_hasattr(dp))
> +		return -ENOATTR;
> +
> +	if (dp->i_afp->if_format == XFS_DINODE_FMT_LOCAL) {
>  		ASSERT(dp->i_afp->if_flags & XFS_IFINLINE);
> -		error = xfs_attr_shortform_remove(args);
> -	} else if (xfs_bmap_one_block(dp, XFS_ATTR_FORK)) {
> -		error = xfs_attr_leaf_removename(args);
> -	} else {
> -		error = xfs_attr_node_removename(args);
> +		return xfs_attr_shortform_remove(args);
>  	}
>  
> -	return error;
> +	if (xfs_bmap_one_block(dp, XFS_ATTR_FORK))
> +		return xfs_attr_leaf_removename(args);
> +node:
> +	/* If we are not short form or leaf, then proceed to remove node */
> +	return  xfs_attr_node_removename_iter(dac);
>  }
>  
>  /*
> @@ -1178,10 +1241,11 @@ xfs_attr_leaf_mark_incomplete(
>   */
>  STATIC
>  int xfs_attr_node_removename_setup(
> -	struct xfs_da_args	*args,
> -	struct xfs_da_state	**state)
> +	struct xfs_delattr_context	*dac)
>  {

In xfs_attr_node_removename_setup(), if either of
xfs_attr_leaf_mark_incomplete() or xfs_attr_rmtval_invalidate() returns with a
non-zero value, the memory pointed to by dac->da_state is not freed. This
happens because the caller (i.e. xfs_attr_node_removename_iter()) checks for
the non-NULL value of its local variable "state" to actually free the
corresponding memory.

> -	int			error;
> +	struct xfs_da_args		*args = dac->da_args;
> +	struct xfs_da_state		**state = &dac->da_state;
> +	int				error;
>  
>  	error = xfs_attr_node_hasname(args, state);
>  	if (error != -EEXIST)
> @@ -1203,13 +1267,16 @@ int xfs_attr_node_removename_setup(
>  }
>  
>  STATIC int
> -xfs_attr_node_remove_rmt(
> -	struct xfs_da_args	*args,
> -	struct xfs_da_state	*state)
> +xfs_attr_node_remove_rmt (
> +	struct xfs_delattr_context	*dac,
> +	struct xfs_da_state		*state)
>  {
> -	int			error = 0;
> +	int				error = 0;
>  
> -	error = xfs_attr_rmtval_remove(args);
> +	/*
> +	 * May return -EAGAIN to request that the caller recall this function
> +	 */
> +	error = __xfs_attr_rmtval_remove(dac);
>  	if (error)
>  		return error;
>  
> @@ -1240,28 +1307,34 @@ xfs_attr_node_remove_cleanup(
>  }
>  
>  /*
> - * Remove a name from a B-tree attribute list.
> + * Step through removeing a name from a B-tree attribute list.
>   *
>   * 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 inline 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_remove_step(
> -	struct xfs_da_args	*args,
> -	struct xfs_da_state	*state)
> +	struct xfs_delattr_context	*dac)
>  {
> -	int			error;
> -	struct xfs_inode	*dp = args->dp;
> -
> -
> +	struct xfs_da_args		*args = dac->da_args;
> +	struct xfs_da_state		*state = dac->da_state;
> +	int				error = 0;
>  	/*
>  	 * 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_node_remove_rmt(args, state);
> +		/*
> +		 * May return -EAGAIN. Remove blocks until args->rmtblkno == 0
> +		 */
> +		error = xfs_attr_node_remove_rmt(dac, state);
>  		if (error)
>  			return error;
>  	}
> @@ -1274,51 +1347,74 @@ xfs_attr_node_remove_step(
>   *
>   * This routine will find the blocks of the name to remove, remove them and
>   * shrink the tree if needed.
> + *
> + * This routine is meant to function as either an inline 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)
> +xfs_attr_node_removename_iter(
> +	struct xfs_delattr_context	*dac)
>  {
> -	struct xfs_da_state	*state = NULL;
> -	int			retval, error;
> -	struct xfs_inode	*dp = args->dp;
> +	struct xfs_da_args		*args = dac->da_args;
> +	struct xfs_da_state		*state = NULL;
> +	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;
> +	if (!dac->da_state) {
> +		error = xfs_attr_node_removename_setup(dac);
> +		if (error)
> +			goto out;
> +	}
> +	state = dac->da_state;
>  
> -	error = xfs_attr_node_remove_step(args, state);
> -	if (error)
> -		goto out;
> +	switch (dac->dela_state) {
> +	case XFS_DAS_UNINIT:
> +		/*
> +		 * repeatedly remove remote blocks, remove the entry and join.
> +		 * returns -EAGAIN or 0 for completion of the step.
> +		 */
> +		error = xfs_attr_node_remove_step(dac);
> +		if (error)
> +			break;
>  
> -	retval = xfs_attr_node_remove_cleanup(args, state);
> +		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)
> -			return error;
> -		error = xfs_defer_finish(&args->trans);
> -		if (error)
> -			return error;
>  		/*
> -		 * 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)
> -			return error;
> -	}
> +		if (retval && (state->path.active > 1)) {
> +			error = xfs_da3_join(state);
> +			if (error)
> +				return error;
>  
> -	/*
> -	 * 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..3154ef4 100644
> --- a/fs/xfs/libxfs/xfs_attr.h
> +++ b/fs/xfs/libxfs/xfs_attr.h
> @@ -74,6 +74,102 @@ 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
> + *        found attr blks? ───n──┐
> + *              │                v
> + *              │         find and invalidate
> + *              y         the blocks. mark
> + *              │         attr incomplete
> + *              ├────────────────┘
> + *              │
> + *              v
> + *      remove a block with
> + *    xfs_attr_node_remove_step <────┐
> + *              │                    │
> + *              v                    │
> + *      still have blks ──y──> return -EAGAIN.
> + *        to remove?          re-enter with one
> + *              │            less blk to remove
> + *              n
> + *              │
> + *              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_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 +187,10 @@ 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..f09820c 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 dont 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 reminicent 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"
> 


-- 
chandan