Re: [PATCH 2/3 V2] xfs: Add infrastructure needed for error propagation during buffer IO failure

[Brian Foster <bfoster@redhat.com>]

On Mon, May 22, 2017 at 05:32:19PM +0200, Carlos Maiolino wrote:
> With the current code, XFS never re-submit a failed buffer for IO,
> because the failed item in the buffer is kept in the flush locked state
> forever.
> 
> To be able to resubmit an log item for IO, we need a way to mark an item
> as failed, if, for any reason the buffer which the item belonged to
> failed during writeback.
> 
> Add a new log item callback to be used after an IO completion failure
> and make the needed clean ups.
> 
> Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
> ---
> V2:
> 	- Update commit log to include a better description of why this
> 	  patch is needed and fix spelling mistakes
> 	- Move xfs_buf_do_callbacks_fail() call into
> 	  xfs_buf_iodone_callback_error, so the callbacks can be executed
> 	  before the buffer is released, and only after it has been
> 	  retried once
> 
>  fs/xfs/xfs_buf_item.c | 27 ++++++++++++++++++++++++++-
>  fs/xfs/xfs_trans.h    |  5 ++++-
>  2 files changed, 30 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/xfs/xfs_buf_item.c b/fs/xfs/xfs_buf_item.c
> index 6ac3816..8f128e3 100644
> --- a/fs/xfs/xfs_buf_item.c
> +++ b/fs/xfs/xfs_buf_item.c
> @@ -1051,6 +1051,24 @@ xfs_buf_do_callbacks(
>  	}
>  }
>  
> +STATIC void
> +xfs_buf_do_callbacks_fail(
> +	struct xfs_buf		*bp)
> +{
> +	struct xfs_log_item	*lip, *next;
> +	unsigned int		bflags = bp->b_flags;
> +
> +	lip = bp->b_fspriv;
> +	while (lip != NULL) {
> +		next = lip->li_bio_list;
> +
> +		if (lip->li_ops->iop_error)
> +			lip->li_ops->iop_error(lip, bflags);
> +
> +		lip = next;
> +	}

AFAICT, this could do something like the following:

	spin_lock(&ailp->xa_lock);
	while (lip != NULL) {
		next = lip->li_bio_list;
		lip->li_flags |= XFS_LI_FAILED;
		lip = next;
	}
	spin_unlock(&ailp->xa_lock);

... to generically and unconditionally flag the log item as failed and
avoid the need for ->iop_error(). We also need to clear XFS_LI_FAILED at
the same place we clear XFS_LI_IN_AIL (i.e., AIL removal) to ensure a
subsequent successful I/O completion updates the log item appropriately.

Then the result of this patch is that all log items are flagged as
failed on I/O error until they are ultimately removed from the AIL. We
otherwise have so far not changed behavior in any way.

Brian

> +}
> +
>  static bool
>  xfs_buf_iodone_callback_error(
>  	struct xfs_buf		*bp)
> @@ -1101,6 +1119,7 @@ xfs_buf_iodone_callback_error(
>  
>  		xfs_buf_ioerror(bp, 0);
>  		xfs_buf_submit(bp);
> +
>  		return true;
>  	}
>  
> @@ -1120,8 +1139,14 @@ xfs_buf_iodone_callback_error(
>  	if ((mp->m_flags & XFS_MOUNT_UNMOUNTING) && mp->m_fail_unmount)
>  		goto permanent_error;
>  
> -	/* still a transient error, higher layers will retry */
> +	/*
> +	 * still a transient error, run IO completion failure callbacks and
> +	 * let the higher layers retry the buffer.
> +	 * */
>  	xfs_buf_ioerror(bp, 0);
> +
> +	/* run failure callbacks before releasing buffer */
> +	xfs_buf_do_callbacks_fail(bp);
>  	xfs_buf_relse(bp);
>  	return true;
>  
> diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h
> index 7ae04de..7fcf48d 100644
> --- a/fs/xfs/xfs_trans.h
> +++ b/fs/xfs/xfs_trans.h
> @@ -65,10 +65,12 @@ typedef struct xfs_log_item {
>  
>  #define	XFS_LI_IN_AIL	0x1
>  #define XFS_LI_ABORTED	0x2
> +#define XFS_LI_FAILED	0x3
>  
>  #define XFS_LI_FLAGS \
>  	{ XFS_LI_IN_AIL,	"IN_AIL" }, \
> -	{ XFS_LI_ABORTED,	"ABORTED" }
> +	{ XFS_LI_ABORTED,	"ABORTED" }, \
> +	{ XFS_LI_FAILED,	"FAILED" }
>  
>  struct xfs_item_ops {
>  	void (*iop_size)(xfs_log_item_t *, int *, int *);
> @@ -79,6 +81,7 @@ struct xfs_item_ops {
>  	void (*iop_unlock)(xfs_log_item_t *);
>  	xfs_lsn_t (*iop_committed)(xfs_log_item_t *, xfs_lsn_t);
>  	void (*iop_committing)(xfs_log_item_t *, xfs_lsn_t);
> +	void (*iop_error)(xfs_log_item_t *, unsigned int bflags);
>  };
>  
>  void	xfs_log_item_init(struct xfs_mount *mp, struct xfs_log_item *item,
> -- 
> 2.9.3
> 
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