Re: [PATCH 1/2 V4] xfs: Add infrastructure needed for error propagation during buffer IO failure

[Brian Foster <bfoster@redhat.com>]

On Fri, Jun 16, 2017 at 12:54:44PM +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
> 
> V3:
> 	- fix some loops according to hch suggestion
> 	- whitespace cleanup
> 
> V4:
> 	- Invoke failure callbacks before reset the I/O error
> 	- Remove bflags field from iop_error callback
> 	- move spin_lock/unlock xa_lock up in the stack, handling all
> 	  log items in the same buffer into a single lock
> 

Looks mostly Ok to me, just a few nits...

>  fs/xfs/xfs_buf_item.c | 23 ++++++++++++++++++++++-
>  fs/xfs/xfs_trans.h    |  7 +++++--
>  2 files changed, 27 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/xfs/xfs_buf_item.c b/fs/xfs/xfs_buf_item.c
> index 0306168..4fa68c9 100644
> --- a/fs/xfs/xfs_buf_item.c
> +++ b/fs/xfs/xfs_buf_item.c
> @@ -29,6 +29,7 @@
>  #include "xfs_error.h"
>  #include "xfs_trace.h"
>  #include "xfs_log.h"
> +#include "xfs_inode.h"
>  
>  
>  kmem_zone_t	*xfs_buf_item_zone;
> @@ -1051,6 +1052,22 @@ xfs_buf_do_callbacks(
>  	}
>  }
>  
> +STATIC void
> +xfs_buf_do_callbacks_fail(
> +	struct xfs_buf		*bp)
> +{
> +	struct xfs_log_item	*tli, *lip, *next;
> +
> +	tli = bp->b_fspriv;

We can just define a local pointer to the xfs_ail rather than maintain a
log item pointer purely for the purpose of the lock. E.g.:

	struct xfs_log_item	*lip = bp->b_fspriv;
	struct xfs_ail		*ailp = lip->li_ailp;

	spin_lock(&ailp->xa_lock);
	for (; lip; lip = next) {
		...
	}
	...

It also couldn't hurt to ASSERT(bp->b_error) somewhere in here.

> +	spin_lock(&tli->li_ailp->xa_lock);
> +	for (lip = bp->b_fspriv; lip; lip = next) {
> +		next = lip->li_bio_list;
> +		if (lip->li_ops->iop_error)
> +			lip->li_ops->iop_error(lip, bp);
> +	}
> +	spin_unlock(&tli->li_ailp->xa_lock);
> +}
> +
>  static bool
>  xfs_buf_iodone_callback_error(
>  	struct xfs_buf		*bp)
> @@ -1120,7 +1137,11 @@ 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_do_callbacks_fail(bp);
>  	xfs_buf_ioerror(bp, 0);
>  	xfs_buf_relse(bp);
>  	return true;
> diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h
> index a07acbf..50df5367 100644
> --- a/fs/xfs/xfs_trans.h
> +++ b/fs/xfs/xfs_trans.h
> @@ -64,11 +64,13 @@ typedef struct xfs_log_item {
>  } xfs_log_item_t;
>  
>  #define	XFS_LI_IN_AIL	0x1
> -#define XFS_LI_ABORTED	0x2
> +#define	XFS_LI_ABORTED	0x2
> +#define	XFS_LI_FAILED	0x4

Weren't you planning to change these to (1 << N) format?

Brian

>  
>  #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 *, xfs_buf_t *);
>  };
>  
>  void	xfs_log_item_init(struct xfs_mount *mp, struct xfs_log_item *item,
> -- 
> 2.9.4
> 
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