Re: [PATCH 3/7] xfs: add configurable error support to metadata buffers

Brian Foster
2016-05-05T14:10:45Z

On Wed, May 04, 2016 at 05:43:16PM +0200, Carlos Maiolino wrote:
> With the error configuration handle for async metadata write errors
> in place, we can now add initial support to the IO error processing
> in xfs_buf_iodone_error().
>
> Add an infrastructure function to look up the configuration handle,
> and rearrange the error handling to prepare the way for different
> error handling conigurations to be used.
>
> Changelog:
>
> V3:
> - in xfs_buf_iodone_callbacks, use cfg->max_retries to
> determine if the filesystem should fail or not, a zero value
> means it should never retry.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
> ---
> fs/xfs/xfs_buf.h | 1 +
> fs/xfs/xfs_buf_item.c | 112 ++++++++++++++++++++++++++++++--------------------
> fs/xfs/xfs_mount.h | 3 ++
> fs/xfs/xfs_sysfs.c | 17 ++++++++
> 4 files changed, 88 insertions(+), 45 deletions(-)
>
> diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
> index 4eb89bd..adef116 100644
> --- a/fs/xfs/xfs_buf.h
> +++ b/fs/xfs/xfs_buf.h
> @@ -183,6 +183,7 @@ typedef struct xfs_buf {
> unsigned int b_page_count; /* size of page array */
> unsigned int b_offset; /* page offset in first page */
> int b_error; /* error code on I/O */
> + int b_last_error; /* previous async I/O error */
> const struct xfs_buf_ops *b_ops;
>
> #ifdef XFS_BUF_LOCK_TRACKING
> diff --git a/fs/xfs/xfs_buf_item.c b/fs/xfs/xfs_buf_item.c
> index 99e91a0..3a30a88 100644
> --- a/fs/xfs/xfs_buf_item.c
> +++ b/fs/xfs/xfs_buf_item.c
> @@ -1042,35 +1042,22 @@ xfs_buf_do_callbacks(
> }
> }
>
> -/*
> - * This is the iodone() function for buffers which have had callbacks
> - * attached to them by xfs_buf_attach_iodone(). It should remove each
> - * log item from the buffer's list and call the callback of each in turn.
> - * When done, the buffer's fsprivate field is set to NULL and the buffer
> - * is unlocked with a call to iodone().
> - */
> -void
> -xfs_buf_iodone_callbacks(
> +static bool
> +xfs_buf_iodone_callback_error(
> struct xfs_buf *bp)
> {
> struct xfs_log_item *lip = bp->b_fspriv;
> struct xfs_mount *mp = lip->li_mountp;
> static ulong lasttime;
> static xfs_buftarg_t *lasttarg;
> -
> - if (likely(!bp->b_error))
> - goto do_callbacks;
> + struct xfs_error_cfg *cfg;
>
> /*
> * If we've already decided to shutdown the filesystem because of
> * I/O errors, there's no point in giving this a retry.
> */
> - if (XFS_FORCED_SHUTDOWN(mp)) {
> - xfs_buf_stale(bp);
> - bp->b_flags |= XBF_DONE;
> - trace_xfs_buf_item_iodone(bp, _RET_IP_);
> - goto do_callbacks;
> - }
> + if (XFS_FORCED_SHUTDOWN(mp))
> + goto out_stale;

Looks like we've lost a trace_xfs_buf_item_iodone() call here. Maybe we
don't really need it, but this is the only caller so we should at least
remove it.

>
> if (bp->b_target != lasttarg ||
> time_after(jiffies, (lasttime + 5*HZ))) {
> @@ -1079,45 +1066,80 @@ xfs_buf_iodone_callbacks(
> }
> lasttarg = bp->b_target;
>
> + /* synchronous writes will have callers process the error */
> + if (!(bp->b_flags & XBF_ASYNC))
> + goto out_stale;
> +
> + trace_xfs_buf_item_iodone_async(bp, _RET_IP_);
> + ASSERT(bp->b_iodone != NULL);
> +
> /*
> * If the write was asynchronous then no one will be looking for the
> - * error. Clear the error state and write the buffer out again.
> - *
> - * XXX: This helps against transient write errors, but we need to find
> - * a way to shut the filesystem down if the writes keep failing.
> - *
> - * In practice we'll shut the filesystem down soon as non-transient
> - * errors tend to affect the whole device and a failing log write
> - * will make us give up. But we really ought to do better here.
> + * error. If this is the first failure of this type, clear the error
> + * state and write the buffer out again. This means we always retry an
> + * async write failure at least once, but we also need to set the buffer
> + * up to behave correctly now for repeated failures.
> */
> - if (bp->b_flags & XBF_ASYNC) {
> - ASSERT(bp->b_iodone != NULL);
> -
> - trace_xfs_buf_item_iodone_async(bp, _RET_IP_);
> + cfg = xfs_error_get_cfg(mp, XFS_ERR_METADATA, bp->b_error);

Can we push this down? We don't use cfg until after the subsequent hunk.

> + if (!(bp->b_flags & (XBF_STALE|XBF_WRITE_FAIL)) ||
> + bp->b_last_error != bp->b_error) {
> + bp->b_flags |= (XBF_WRITE | XBF_ASYNC |
> + XBF_DONE | XBF_WRITE_FAIL);
> + bp->b_last_error = bp->b_error;
> + xfs_buf_ioerror(bp, 0);
> + xfs_buf_submit(bp);
> + return true;
> + }
>
> - xfs_buf_ioerror(bp, 0); /* errno of 0 unsets the flag */
> + /*
> + * Repeated failure on an async write. Take action according to the
> + * error configuration we have been set up to use.
> + */
> + if (!cfg->max_retries)
> + goto permanent_error;
>
> - if (!(bp->b_flags & (XBF_STALE|XBF_WRITE_FAIL))) {
> - bp->b_flags |= XBF_WRITE | XBF_ASYNC |
> - XBF_DONE | XBF_WRITE_FAIL;
> - xfs_buf_submit(bp);
> - } else {
> - xfs_buf_relse(bp);
> - }
> -
> - return;
> - }
> + /* still a transient error, higher layers will retry */
> + xfs_buf_ioerror(bp, 0);
> + xfs_buf_relse(bp);
> + return true;
>
> /*
> - * If the write of the buffer was synchronous, we want to make
> - * sure to return the error to the caller of xfs_bwrite().
> + * Permanent error - we need to trigger a shutdown if we haven't already
> + * to indicate that inconsistency will result from this action.
> */
> +permanent_error:
> + xfs_force_shutdown(mp, SHUTDOWN_META_IO_ERROR);
> +out_stale:
> xfs_buf_stale(bp);
> bp->b_flags |= XBF_DONE;
> -
> trace_xfs_buf_error_relse(bp, _RET_IP_);
> + return false;
> +}
> +
> +/*
> + * This is the iodone() function for buffers which have had callbacks attached
> + * to them by xfs_buf_attach_iodone(). We need to iterate the items on the
> + * callback list, mark the buffer as having no more callbacks and then push the
> + * buffer through IO completion processing.
> + */
> +void
> +xfs_buf_iodone_callbacks(
> + struct xfs_buf *bp)
> +{
> + /*
> + * If there is an error, process it. Some errors require us
> + * to run callbacks after failure processing is done so we
> + * detect that and take appropriate action.
> + */
> + if (bp->b_error && xfs_buf_iodone_callback_error(bp))
> + return;

Just a nit, but I'm not a fan of this kind of logic just because it
tends to obfuscate the fact that a function is being called. Could we
make it look something like the following?

/* ... */
if (bp->b_error) {
if (xfs_buf_iodone_callback_error(bp))
return;
}

Also FWIW, the return value logic of "return if true" seems a little
weird to me because I read it as "don't do something if true." The
inverse ("run callbacks if true") is more clear, IMO, but that's not a
big deal.

Brian

> +
> + /*
> + * Successful IO or permanent error. Either way, we can clear the
> + * retry state here in preparation for the next error that may occur.
> + */
> + bp->b_last_error = 0;
>
> -do_callbacks:
> xfs_buf_do_callbacks(bp);
> bp->b_fspriv = NULL;
> bp->b_iodone = NULL;
> diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
> index 352a5c8..0c5a976 100644
> --- a/fs/xfs/xfs_mount.h
> +++ b/fs/xfs/xfs_mount.h
> @@ -387,4 +387,7 @@ extern void xfs_set_low_space_thresholds(struct xfs_mount *);
> int xfs_zero_extent(struct xfs_inode *ip, xfs_fsblock_t start_fsb,
> xfs_off_t count_fsb);
>
> +struct xfs_error_cfg * xfs_error_get_cfg(struct xfs_mount *mp,
> + int error_class, int error);
> +
> #endif /* __XFS_MOUNT_H__ */
> diff --git a/fs/xfs/xfs_sysfs.c b/fs/xfs/xfs_sysfs.c
> index 7180cff..0a9adcd 100644
> --- a/fs/xfs/xfs_sysfs.c
> +++ b/fs/xfs/xfs_sysfs.c
> @@ -447,3 +447,20 @@ xfs_error_sysfs_del(
> xfs_sysfs_del(&mp->m_error_meta_kobj);
> xfs_sysfs_del(&mp->m_error_kobj);
> }
> +
> +struct xfs_error_cfg *
> +xfs_error_get_cfg(
> + struct xfs_mount *mp,
> + int error_class,
> + int error)
> +{
> + struct xfs_error_cfg *cfg;
> +
> + switch (error) {
> + default:
> + cfg = &mp->m_error_cfg[error_class][XFS_ERR_DEFAULT];
> + break;
> + }
> +
> + return cfg;
> +}
> --
> 2.4.11
>
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