Re: [PATCH 06/24] xfs: call xfs_buf_iodone directly

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Fri, May 22, 2020 at 01:50:11PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> All unmarked dirty buffers should be in the AIL and have log items
> attached to them. Hence when they are written, we will run a
> callback to remove the item from the AIL if appropriate. Now that
> we've handled inode and dquot buffers, all remaining calls are to
> xfs_buf_iodone() and so we can hard code this rather than use an
> indirect call.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
>  fs/xfs/xfs_buf.c       | 24 +++++++++---------------
>  fs/xfs/xfs_buf.h       |  6 +-----
>  fs/xfs/xfs_buf_item.c  | 38 +++++++++-----------------------------
>  fs/xfs/xfs_buf_item.h  |  2 +-
>  fs/xfs/xfs_trans_buf.c |  9 +--------
>  5 files changed, 21 insertions(+), 58 deletions(-)
> 
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index b89685ce8519d..5fc83637f7aff 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -658,7 +658,6 @@ xfs_buf_find(
>  	 */
>  	if (bp->b_flags & XBF_STALE) {
>  		ASSERT((bp->b_flags & _XBF_DELWRI_Q) == 0);
> -		ASSERT(bp->b_iodone == NULL);
>  		bp->b_flags &= _XBF_KMEM | _XBF_PAGES;
>  		bp->b_ops = NULL;
>  	}
> @@ -1194,10 +1193,13 @@ xfs_buf_ioend(
>  	if (!bp->b_error && bp->b_io_error)
>  		xfs_buf_ioerror(bp, bp->b_io_error);
>  
> -	/* Only validate buffers that were read without errors */
> -	if (read && !bp->b_error && bp->b_ops) {
> -		ASSERT(!bp->b_iodone);
> -		bp->b_ops->verify_read(bp);
> +	if (read) {
> +		if (!bp->b_error && bp->b_ops)
> +			bp->b_ops->verify_read(bp);
> +		if (!bp->b_error)
> +			bp->b_flags |= XBF_DONE;
> +		xfs_buf_ioend_finish(bp);
> +		return;
>  	}
>  
>  	if (!bp->b_error) {
> @@ -1205,9 +1207,6 @@ xfs_buf_ioend(
>  		bp->b_flags |= XBF_DONE;
>  	}
>  
> -	if (read)
> -		goto out_finish;
> -
>  	/*
>  	 * If this is a log recovery buffer, we aren't doing transactional IO
>  	 * yet so we need to let it handle IO completions.
> @@ -1229,13 +1228,8 @@ xfs_buf_ioend(
>  		return;
>  	}
>  
> -	if (bp->b_iodone) {
> -		(*(bp->b_iodone))(bp);
> -		return;
> -	}
> -
> -out_finish:
> -	xfs_buf_ioend_finish(bp);
> +	/* dirty buffers always need to be removed from the AIL */
> +	xfs_buf_dirty_iodone(bp);
>  }
>  
>  static void
> diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
> index c5fe4c48c9080..a127d56d5eff0 100644
> --- a/fs/xfs/xfs_buf.h
> +++ b/fs/xfs/xfs_buf.h
> @@ -18,6 +18,7 @@
>  /*
>   *	Base types
>   */
> +struct xfs_buf;
>  
>  #define XFS_BUF_DADDR_NULL	((xfs_daddr_t) (-1LL))
>  
> @@ -103,10 +104,6 @@ typedef struct xfs_buftarg {
>  	struct ratelimit_state	bt_ioerror_rl;
>  } xfs_buftarg_t;
>  
> -struct xfs_buf;
> -typedef void (*xfs_buf_iodone_t)(struct xfs_buf *);
> -
> -
>  #define XB_PAGES	2
>  
>  struct xfs_buf_map {
> @@ -159,7 +156,6 @@ typedef struct xfs_buf {
>  	xfs_buftarg_t		*b_target;	/* buffer target (device) */
>  	void			*b_addr;	/* virtual address of buffer */
>  	struct work_struct	b_ioend_work;
> -	xfs_buf_iodone_t	b_iodone;	/* I/O completion function */
>  	struct completion	b_iowait;	/* queue for I/O waiters */
>  	struct xfs_buf_log_item	*b_log_item;
>  	struct list_head	b_li_list;	/* Log items list head */
> diff --git a/fs/xfs/xfs_buf_item.c b/fs/xfs/xfs_buf_item.c
> index a42cdf9ccc47d..c2e7d14e35c66 100644
> --- a/fs/xfs/xfs_buf_item.c
> +++ b/fs/xfs/xfs_buf_item.c
> @@ -460,7 +460,6 @@ xfs_buf_item_unpin(
>  			xfs_buf_do_callbacks(bp);
>  			bp->b_log_item = NULL;
>  			list_del_init(&bp->b_li_list);
> -			bp->b_iodone = NULL;
>  		} else {
>  			xfs_trans_ail_delete(lip, SHUTDOWN_LOG_IO_ERROR);
>  			xfs_buf_item_relse(bp);
> @@ -936,11 +935,7 @@ xfs_buf_item_free(
>  }
>  
>  /*
> - * This is called when the buf log item is no longer needed.  It should
> - * free the buf log item associated with the given buffer and clear
> - * the buffer's pointer to the buf log item.  If there are no more
> - * items in the list, clear the b_iodone field of the buffer (see
> - * xfs_buf_attach_iodone() below).
> + * xfs_buf_item_relse() is called when the buf log item is no longer needed.
>   */
>  void
>  xfs_buf_item_relse(
> @@ -952,9 +947,6 @@ xfs_buf_item_relse(
>  	ASSERT(!test_bit(XFS_LI_IN_AIL, &bip->bli_item.li_flags));
>  
>  	bp->b_log_item = NULL;
> -	if (list_empty(&bp->b_li_list))
> -		bp->b_iodone = NULL;
> -
>  	xfs_buf_rele(bp);
>  	xfs_buf_item_free(bip);
>  }
> @@ -962,10 +954,7 @@ xfs_buf_item_relse(
>  
>  /*
>   * Add the given log item with its callback to the list of callbacks
> - * to be called when the buffer's I/O completes.  If it is not set
> - * already, set the buffer's b_iodone() routine to be
> - * xfs_buf_iodone_callbacks() and link the log item into the list of
> - * items rooted at b_li_list.
> + * to be called when the buffer's I/O completes.
>   */
>  void
>  xfs_buf_attach_iodone(
> @@ -977,10 +966,6 @@ xfs_buf_attach_iodone(
>  
>  	lip->li_cb = cb;
>  	list_add_tail(&lip->li_bio_list, &bp->b_li_list);
> -
> -	ASSERT(bp->b_iodone == NULL ||
> -	       bp->b_iodone == xfs_buf_iodone_callbacks);
> -	bp->b_iodone = xfs_buf_iodone_callbacks;
>  }
>  
>  /*
> @@ -1096,7 +1081,6 @@ xfs_buf_iodone_callback_error(
>  		goto out_stale;
>  
>  	trace_xfs_buf_item_iodone_async(bp, _RET_IP_);
> -	ASSERT(bp->b_iodone != NULL);
>  
>  	cfg = xfs_error_get_cfg(mp, XFS_ERR_METADATA, bp->b_error);
>  
> @@ -1182,28 +1166,24 @@ xfs_buf_run_callbacks(
>  	xfs_buf_do_callbacks(bp);
>  	bp->b_log_item = NULL;
>  	list_del_init(&bp->b_li_list);
> -	bp->b_iodone = NULL;
>  }
>  
>  /*
> - * 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.
> + * Inode buffer iodone callback function.
>   */
>  void
> -xfs_buf_iodone_callbacks(
> +xfs_buf_inode_iodone(
>  	struct xfs_buf		*bp)
>  {
>  	xfs_buf_run_callbacks(bp);
> -	xfs_buf_ioend(bp);
> +	xfs_buf_ioend_finish(bp);
>  }
>  
>  /*
> - * Inode buffer iodone callback function.
> + * Dquot buffer iodone callback function.
>   */
>  void
> -xfs_buf_inode_iodone(
> +xfs_buf_dquot_iodone(
>  	struct xfs_buf		*bp)
>  {
>  	xfs_buf_run_callbacks(bp);
> @@ -1211,10 +1191,10 @@ xfs_buf_inode_iodone(
>  }
>  
>  /*
> - * Dquot buffer iodone callback function.
> + * Dirty buffer iodone callback function.
>   */
>  void
> -xfs_buf_dquot_iodone(
> +xfs_buf_dirty_iodone(

git diff --patience would make the relatively little change going on
here much clearer:

@@ -1182,21 +1166,6 @@ xfs_buf_run_callbacks(
        xfs_buf_do_callbacks(bp);
        bp->b_log_item = NULL;
        list_del_init(&bp->b_li_list);
-       bp->b_iodone = NULL;
-}
-
-/*
- * 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)
-{
-       xfs_buf_run_callbacks(bp);
-       xfs_buf_ioend(bp);
 }
 
 /*
@@ -1221,6 +1190,17 @@ xfs_buf_dquot_iodone(
        xfs_buf_ioend_finish(bp);
 }
 
+/*
+ * Dirty buffer iodone callback function.
+ */
+void
+xfs_buf_dirty_iodone(
+       struct xfs_buf          *bp)
+{
+       xfs_buf_run_callbacks(bp);
+       xfs_buf_ioend_finish(bp);
+}
+
 /*
  * This is the iodone() function for buffers which have been
  * logged.  It is called when they are eventually flushed out.

OTOH all the searching I had to do to figure out what was really going
on here persuaded me to go look at what this looked like at the end, so
I guess I'm not that worried.

Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D


>  	struct xfs_buf		*bp)
>  {
>  	xfs_buf_run_callbacks(bp);
> diff --git a/fs/xfs/xfs_buf_item.h b/fs/xfs/xfs_buf_item.h
> index 27d13d29b5bbb..96f994ec90915 100644
> --- a/fs/xfs/xfs_buf_item.h
> +++ b/fs/xfs/xfs_buf_item.h
> @@ -57,10 +57,10 @@ bool	xfs_buf_item_dirty_format(struct xfs_buf_log_item *);
>  void	xfs_buf_attach_iodone(struct xfs_buf *,
>  			      void(*)(struct xfs_buf *, struct xfs_log_item *),
>  			      struct xfs_log_item *);
> -void	xfs_buf_iodone_callbacks(struct xfs_buf *);
>  void	xfs_buf_iodone(struct xfs_buf *, struct xfs_log_item *);
>  void	xfs_buf_inode_iodone(struct xfs_buf *);
>  void	xfs_buf_dquot_iodone(struct xfs_buf *);
> +void	xfs_buf_dirty_iodone(struct xfs_buf *);
>  bool	xfs_buf_log_check_iovec(struct xfs_log_iovec *iovec);
>  
>  extern kmem_zone_t	*xfs_buf_item_zone;
> diff --git a/fs/xfs/xfs_trans_buf.c b/fs/xfs/xfs_trans_buf.c
> index 93d62cb864c15..69e0ebe94a915 100644
> --- a/fs/xfs/xfs_trans_buf.c
> +++ b/fs/xfs/xfs_trans_buf.c
> @@ -465,23 +465,16 @@ xfs_trans_dirty_buf(
>  
>  	ASSERT(bp->b_transp == tp);
>  	ASSERT(bip != NULL);
> -	ASSERT(bp->b_iodone == NULL ||
> -	       bp->b_iodone == xfs_buf_iodone_callbacks);
>  
>  	/*
>  	 * Mark the buffer as needing to be written out eventually,
>  	 * and set its iodone function to remove the buffer's buf log
>  	 * item from the AIL and free it when the buffer is flushed
> -	 * to disk.  See xfs_buf_attach_iodone() for more details
> -	 * on li_cb and xfs_buf_iodone_callbacks().
> -	 * If we end up aborting this transaction, we trap this buffer
> -	 * inside the b_bdstrat callback so that this won't get written to
> -	 * disk.
> +	 * to disk.
>  	 */
>  	bp->b_flags |= XBF_DONE;
>  
>  	ASSERT(atomic_read(&bip->bli_refcount) > 0);
> -	bp->b_iodone = xfs_buf_iodone_callbacks;
>  	bip->bli_item.li_cb = xfs_buf_iodone;
>  
>  	/*
> -- 
> 2.26.2.761.g0e0b3e54be
>