[PATCH 0/2] xfs_buf_submit[_wait]() cleanups

[PATCH 0/2] xfs_buf_submit[_wait]() cleanups

[Brian Foster]

These are just a couple cleanups for buffer I/O submission based on
suggestions from Christoph. This applies on top of the previously posted
delwri queue fix [1].

The combination of both slightly circuitously condenses the buf
submission path back into a single helper, but we end up in the same
place either way. I'm sending this separately because review of the
value of this interface refactor is independent of the internal refactor
required to implement the aforementioned bug fix.

Thoughts, reviews, flames appreciated.

[1] https://marc.info/?l=linux-xfs&m=152908593803756&w=2

Brian

Brian Foster (2):
  xfs: combine [a]sync buffer submission apis
  xfs: kill __xfs_buf_submit_common()

 fs/xfs/xfs_buf.c         | 125 +++++++++++++--------------------------
 fs/xfs/xfs_buf.h         |  10 +++-
 fs/xfs/xfs_log_recover.c |   4 +-
 3 files changed, 52 insertions(+), 87 deletions(-)

-- 
2.17.1

[PATCH 1/2] xfs: combine [a]sync buffer submission apis

[Brian Foster]

The buffer I/O submission path consists of separate function calls
per type. The buffer I/O type is already controlled via buffer
state (XBF_ASYNC), however, so there is no real need for separate
submission functions.

Combine the buffer submission functions into a single function that
processes the buffer appropriately based on XBF_ASYNC. Retain an
internal helper with a conditional wait parameter to continue to
support batched !XBF_ASYNC submission/completion required by delwri
queues.

Suggested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Brian Foster <bfoster@redhat.com>
---
 fs/xfs/xfs_buf.c         | 72 +++++++++++++---------------------------
 fs/xfs/xfs_buf.h         | 10 ++++--
 fs/xfs/xfs_log_recover.c |  4 +--
 3 files changed, 33 insertions(+), 53 deletions(-)

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index b5c0f6949b30..64a9a09013e3 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -757,11 +757,7 @@ _xfs_buf_read(
 	bp->b_flags &= ~(XBF_WRITE | XBF_ASYNC | XBF_READ_AHEAD);
 	bp->b_flags |= flags & (XBF_READ | XBF_ASYNC | XBF_READ_AHEAD);
 
-	if (flags & XBF_ASYNC) {
-		xfs_buf_submit(bp);
-		return 0;
-	}
-	return xfs_buf_submit_wait(bp);
+	return xfs_buf_submit(bp);
 }
 
 xfs_buf_t *
@@ -846,7 +842,7 @@ xfs_buf_read_uncached(
 	bp->b_flags |= XBF_READ;
 	bp->b_ops = ops;
 
-	xfs_buf_submit_wait(bp);
+	xfs_buf_submit(bp);
 	if (bp->b_error) {
 		int	error = bp->b_error;
 		xfs_buf_relse(bp);
@@ -1249,7 +1245,7 @@ xfs_bwrite(
 	bp->b_flags &= ~(XBF_ASYNC | XBF_READ | _XBF_DELWRI_Q |
 			 XBF_WRITE_FAIL | XBF_DONE);
 
-	error = xfs_buf_submit_wait(bp);
+	error = xfs_buf_submit(bp);
 	if (error) {
 		xfs_force_shutdown(bp->b_target->bt_mount,
 				   SHUTDOWN_META_IO_ERROR);
@@ -1459,7 +1455,7 @@ _xfs_buf_ioapply(
  * itself.
  */
 static int
-__xfs_buf_submit(
+__xfs_buf_submit_common(
 	struct xfs_buf	*bp)
 {
 	trace_xfs_buf_submit(bp, _RET_IP_);
@@ -1505,32 +1501,6 @@ __xfs_buf_submit(
 	return 0;
 }
 
-void
-xfs_buf_submit(
-	struct xfs_buf	*bp)
-{
-	int		error;
-
-	ASSERT(bp->b_flags & XBF_ASYNC);
-
-	/*
-	 * The caller's reference is released during I/O completion.
-	 * This occurs some time after the last b_io_remaining reference is
-	 * released, so after we drop our Io reference we have to have some
-	 * other reference to ensure the buffer doesn't go away from underneath
-	 * us. Take a direct reference to ensure we have safe access to the
-	 * buffer until we are finished with it.
-	 */
-	xfs_buf_hold(bp);
-
-	error = __xfs_buf_submit(bp);
-	if (error)
-		xfs_buf_ioend(bp);
-
-	/* Note: it is not safe to reference bp now we've dropped our ref */
-	xfs_buf_rele(bp);
-}
-
 /*
  * Wait for I/O completion of a sync buffer and return the I/O error code.
  */
@@ -1538,6 +1508,8 @@ static int
 xfs_buf_iowait(
 	struct xfs_buf	*bp)
 {
+	ASSERT(!(bp->b_flags & XBF_ASYNC));
+
 	trace_xfs_buf_iowait(bp, _RET_IP_);
 	wait_for_completion(&bp->b_iowait);
 	trace_xfs_buf_iowait_done(bp, _RET_IP_);
@@ -1549,30 +1521,33 @@ xfs_buf_iowait(
  * Synchronous buffer IO submission path, read or write.
  */
 int
-xfs_buf_submit_wait(
-	struct xfs_buf	*bp)
+__xfs_buf_submit(
+	struct xfs_buf	*bp,
+	bool		wait)
 {
 	int		error;
 
-	ASSERT(!(bp->b_flags & XBF_ASYNC));
-
 	/*
-	 * For synchronous IO, the IO does not inherit the submitters reference
-	 * count, nor the buffer lock. Hence we cannot release the reference we
-	 * are about to take until we've waited for all IO completion to occur,
-	 * including any xfs_buf_ioend_async() work that may be pending.
+	 * Grab a reference so the buffer does not go away underneath us. For
+	 * async buffers, I/O completion drops the callers reference, which
+	 * could occur before submission returns.
 	 */
 	xfs_buf_hold(bp);
 
-	error = __xfs_buf_submit(bp);
-	if (error)
+	error = __xfs_buf_submit_common(bp);
+	if (error) {
+		if (bp->b_flags & XBF_ASYNC)
+			xfs_buf_ioend(bp);
 		goto out;
-	error = xfs_buf_iowait(bp);
+	}
 
+	if (wait)
+		error = xfs_buf_iowait(bp);
 out:
 	/*
-	 * all done now, we can release the hold that keeps the buffer
-	 * referenced for the entire IO.
+	 * Release the hold that keeps the buffer referenced for the entire
+	 * I/O. Note that if the buffer is async, it is not safe to reference
+	 * after this release.
 	 */
 	xfs_buf_rele(bp);
 	return error;
@@ -2026,12 +2001,11 @@ xfs_buf_delwri_submit_buffers(
 		if (wait_list) {
 			bp->b_flags &= ~XBF_ASYNC;
 			list_move_tail(&bp->b_list, wait_list);
-			__xfs_buf_submit(bp);
 		} else {
 			bp->b_flags |= XBF_ASYNC;
 			list_del_init(&bp->b_list);
-			xfs_buf_submit(bp);
 		}
+		__xfs_buf_submit(bp, false);
 	}
 	blk_finish_plug(&plug);
 
diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
index d24dbd4dac39..a57693a5cdd7 100644
--- a/fs/xfs/xfs_buf.h
+++ b/fs/xfs/xfs_buf.h
@@ -298,8 +298,14 @@ extern void __xfs_buf_ioerror(struct xfs_buf *bp, int error,
 		xfs_failaddr_t failaddr);
 #define xfs_buf_ioerror(bp, err) __xfs_buf_ioerror((bp), (err), __this_address)
 extern void xfs_buf_ioerror_alert(struct xfs_buf *, const char *func);
-extern void xfs_buf_submit(struct xfs_buf *bp);
-extern int xfs_buf_submit_wait(struct xfs_buf *bp);
+
+extern int __xfs_buf_submit(struct xfs_buf *bp, bool);
+static inline int xfs_buf_submit(struct xfs_buf *bp)
+{
+	bool wait = bp->b_flags & XBF_ASYNC ? false : true;
+	return __xfs_buf_submit(bp, wait);
+}
+
 extern void xfs_buf_iomove(xfs_buf_t *, size_t, size_t, void *,
 				xfs_buf_rw_t);
 #define xfs_buf_zero(bp, off, len) \
diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
index b181b5f57a19..724a76d87564 100644
--- a/fs/xfs/xfs_log_recover.c
+++ b/fs/xfs/xfs_log_recover.c
@@ -196,7 +196,7 @@ xlog_bread_noalign(
 	bp->b_io_length = nbblks;
 	bp->b_error = 0;
 
-	error = xfs_buf_submit_wait(bp);
+	error = xfs_buf_submit(bp);
 	if (error && !XFS_FORCED_SHUTDOWN(log->l_mp))
 		xfs_buf_ioerror_alert(bp, __func__);
 	return error;
@@ -5707,7 +5707,7 @@ xlog_do_recover(
 	bp->b_flags |= XBF_READ;
 	bp->b_ops = &xfs_sb_buf_ops;
 
-	error = xfs_buf_submit_wait(bp);
+	error = xfs_buf_submit(bp);
 	if (error) {
 		if (!XFS_FORCED_SHUTDOWN(mp)) {
 			xfs_buf_ioerror_alert(bp, __func__);
-- 
2.17.1

[PATCH 2/2] xfs: kill __xfs_buf_submit_common()

[Brian Foster]

Now that there is only one caller, fold the common submission helper
into __xfs_buf_submit().

Suggested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Brian Foster <bfoster@redhat.com>
---
 fs/xfs/xfs_buf.c | 83 ++++++++++++++++++++----------------------------
 1 file changed, 34 insertions(+), 49 deletions(-)

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 64a9a09013e3..f747792038dc 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -1449,15 +1449,34 @@ _xfs_buf_ioapply(
 }
 
 /*
- * Asynchronous IO submission path. This transfers the buffer lock ownership and
- * the current reference to the IO. It is not safe to reference the buffer after
- * a call to this function unless the caller holds an additional reference
- * itself.
+ * Wait for I/O completion of a sync buffer and return the I/O error code.
  */
 static int
-__xfs_buf_submit_common(
+xfs_buf_iowait(
 	struct xfs_buf	*bp)
 {
+	ASSERT(!(bp->b_flags & XBF_ASYNC));
+
+	trace_xfs_buf_iowait(bp, _RET_IP_);
+	wait_for_completion(&bp->b_iowait);
+	trace_xfs_buf_iowait_done(bp, _RET_IP_);
+
+	return bp->b_error;
+}
+
+/*
+ * Buffer I/O submission path, read or write. Asynchronous submission transfers
+ * the buffer lock ownership and the current reference to the IO. It is not
+ * safe to reference the buffer after a call to this function unless the caller
+ * holds an additional reference itself.
+ */
+int
+__xfs_buf_submit(
+	struct xfs_buf	*bp,
+	bool		wait)
+{
+	int		error = 0;
+
 	trace_xfs_buf_submit(bp, _RET_IP_);
 
 	ASSERT(!(bp->b_flags & _XBF_DELWRI_Q));
@@ -1467,9 +1486,18 @@ __xfs_buf_submit_common(
 		xfs_buf_ioerror(bp, -EIO);
 		bp->b_flags &= ~XBF_DONE;
 		xfs_buf_stale(bp);
+		if (bp->b_flags & XBF_ASYNC)
+			xfs_buf_ioend(bp);
 		return -EIO;
 	}
 
+	/*
+	 * Grab a reference so the buffer does not go away underneath us. For
+	 * async buffers, I/O completion drops the callers reference, which
+	 * could occur before submission returns.
+	 */
+	xfs_buf_hold(bp);
+
 	if (bp->b_flags & XBF_WRITE)
 		xfs_buf_wait_unpin(bp);
 
@@ -1498,52 +1526,9 @@ __xfs_buf_submit_common(
 			xfs_buf_ioend_async(bp);
 	}
 
-	return 0;
-}
-
-/*
- * Wait for I/O completion of a sync buffer and return the I/O error code.
- */
-static int
-xfs_buf_iowait(
-	struct xfs_buf	*bp)
-{
-	ASSERT(!(bp->b_flags & XBF_ASYNC));
-
-	trace_xfs_buf_iowait(bp, _RET_IP_);
-	wait_for_completion(&bp->b_iowait);
-	trace_xfs_buf_iowait_done(bp, _RET_IP_);
-
-	return bp->b_error;
-}
-
-/*
- * Synchronous buffer IO submission path, read or write.
- */
-int
-__xfs_buf_submit(
-	struct xfs_buf	*bp,
-	bool		wait)
-{
-	int		error;
-
-	/*
-	 * Grab a reference so the buffer does not go away underneath us. For
-	 * async buffers, I/O completion drops the callers reference, which
-	 * could occur before submission returns.
-	 */
-	xfs_buf_hold(bp);
-
-	error = __xfs_buf_submit_common(bp);
-	if (error) {
-		if (bp->b_flags & XBF_ASYNC)
-			xfs_buf_ioend(bp);
-		goto out;
-	}
-
 	if (wait)
 		error = xfs_buf_iowait(bp);
-out:
+
 	/*
 	 * Release the hold that keeps the buffer referenced for the entire
 	 * I/O. Note that if the buffer is async, it is not safe to reference
-- 
2.17.1

Re: [PATCH 1/2] xfs: combine [a]sync buffer submission apis

[Darrick J. Wong]

On Mon, Jun 18, 2018 at 10:52:43AM -0400, Brian Foster wrote:
> The buffer I/O submission path consists of separate function calls
> per type. The buffer I/O type is already controlled via buffer
> state (XBF_ASYNC), however, so there is no real need for separate
> submission functions.
> 
> Combine the buffer submission functions into a single function that
> processes the buffer appropriately based on XBF_ASYNC. Retain an
> internal helper with a conditional wait parameter to continue to
> support batched !XBF_ASYNC submission/completion required by delwri
> queues.
> 
> Suggested-by: Christoph Hellwig <hch@infradead.org>
> Signed-off-by: Brian Foster <bfoster@redhat.com>

Looks straightforward enough to test,
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> ---
>  fs/xfs/xfs_buf.c         | 72 +++++++++++++---------------------------
>  fs/xfs/xfs_buf.h         | 10 ++++--
>  fs/xfs/xfs_log_recover.c |  4 +--
>  3 files changed, 33 insertions(+), 53 deletions(-)
> 
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index b5c0f6949b30..64a9a09013e3 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -757,11 +757,7 @@ _xfs_buf_read(
>  	bp->b_flags &= ~(XBF_WRITE | XBF_ASYNC | XBF_READ_AHEAD);
>  	bp->b_flags |= flags & (XBF_READ | XBF_ASYNC | XBF_READ_AHEAD);
>  
> -	if (flags & XBF_ASYNC) {
> -		xfs_buf_submit(bp);
> -		return 0;
> -	}
> -	return xfs_buf_submit_wait(bp);
> +	return xfs_buf_submit(bp);
>  }
>  
>  xfs_buf_t *
> @@ -846,7 +842,7 @@ xfs_buf_read_uncached(
>  	bp->b_flags |= XBF_READ;
>  	bp->b_ops = ops;
>  
> -	xfs_buf_submit_wait(bp);
> +	xfs_buf_submit(bp);
>  	if (bp->b_error) {
>  		int	error = bp->b_error;
>  		xfs_buf_relse(bp);
> @@ -1249,7 +1245,7 @@ xfs_bwrite(
>  	bp->b_flags &= ~(XBF_ASYNC | XBF_READ | _XBF_DELWRI_Q |
>  			 XBF_WRITE_FAIL | XBF_DONE);
>  
> -	error = xfs_buf_submit_wait(bp);
> +	error = xfs_buf_submit(bp);
>  	if (error) {
>  		xfs_force_shutdown(bp->b_target->bt_mount,
>  				   SHUTDOWN_META_IO_ERROR);
> @@ -1459,7 +1455,7 @@ _xfs_buf_ioapply(
>   * itself.
>   */
>  static int
> -__xfs_buf_submit(
> +__xfs_buf_submit_common(
>  	struct xfs_buf	*bp)
>  {
>  	trace_xfs_buf_submit(bp, _RET_IP_);
> @@ -1505,32 +1501,6 @@ __xfs_buf_submit(
>  	return 0;
>  }
>  
> -void
> -xfs_buf_submit(
> -	struct xfs_buf	*bp)
> -{
> -	int		error;
> -
> -	ASSERT(bp->b_flags & XBF_ASYNC);
> -
> -	/*
> -	 * The caller's reference is released during I/O completion.
> -	 * This occurs some time after the last b_io_remaining reference is
> -	 * released, so after we drop our Io reference we have to have some
> -	 * other reference to ensure the buffer doesn't go away from underneath
> -	 * us. Take a direct reference to ensure we have safe access to the
> -	 * buffer until we are finished with it.
> -	 */
> -	xfs_buf_hold(bp);
> -
> -	error = __xfs_buf_submit(bp);
> -	if (error)
> -		xfs_buf_ioend(bp);
> -
> -	/* Note: it is not safe to reference bp now we've dropped our ref */
> -	xfs_buf_rele(bp);
> -}
> -
>  /*
>   * Wait for I/O completion of a sync buffer and return the I/O error code.
>   */
> @@ -1538,6 +1508,8 @@ static int
>  xfs_buf_iowait(
>  	struct xfs_buf	*bp)
>  {
> +	ASSERT(!(bp->b_flags & XBF_ASYNC));
> +
>  	trace_xfs_buf_iowait(bp, _RET_IP_);
>  	wait_for_completion(&bp->b_iowait);
>  	trace_xfs_buf_iowait_done(bp, _RET_IP_);
> @@ -1549,30 +1521,33 @@ xfs_buf_iowait(
>   * Synchronous buffer IO submission path, read or write.
>   */
>  int
> -xfs_buf_submit_wait(
> -	struct xfs_buf	*bp)
> +__xfs_buf_submit(
> +	struct xfs_buf	*bp,
> +	bool		wait)
>  {
>  	int		error;
>  
> -	ASSERT(!(bp->b_flags & XBF_ASYNC));
> -
>  	/*
> -	 * For synchronous IO, the IO does not inherit the submitters reference
> -	 * count, nor the buffer lock. Hence we cannot release the reference we
> -	 * are about to take until we've waited for all IO completion to occur,
> -	 * including any xfs_buf_ioend_async() work that may be pending.
> +	 * Grab a reference so the buffer does not go away underneath us. For
> +	 * async buffers, I/O completion drops the callers reference, which
> +	 * could occur before submission returns.
>  	 */
>  	xfs_buf_hold(bp);
>  
> -	error = __xfs_buf_submit(bp);
> -	if (error)
> +	error = __xfs_buf_submit_common(bp);
> +	if (error) {
> +		if (bp->b_flags & XBF_ASYNC)
> +			xfs_buf_ioend(bp);
>  		goto out;
> -	error = xfs_buf_iowait(bp);
> +	}
>  
> +	if (wait)
> +		error = xfs_buf_iowait(bp);
>  out:
>  	/*
> -	 * all done now, we can release the hold that keeps the buffer
> -	 * referenced for the entire IO.
> +	 * Release the hold that keeps the buffer referenced for the entire
> +	 * I/O. Note that if the buffer is async, it is not safe to reference
> +	 * after this release.
>  	 */
>  	xfs_buf_rele(bp);
>  	return error;
> @@ -2026,12 +2001,11 @@ xfs_buf_delwri_submit_buffers(
>  		if (wait_list) {
>  			bp->b_flags &= ~XBF_ASYNC;
>  			list_move_tail(&bp->b_list, wait_list);
> -			__xfs_buf_submit(bp);
>  		} else {
>  			bp->b_flags |= XBF_ASYNC;
>  			list_del_init(&bp->b_list);
> -			xfs_buf_submit(bp);
>  		}
> +		__xfs_buf_submit(bp, false);
>  	}
>  	blk_finish_plug(&plug);
>  
> diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
> index d24dbd4dac39..a57693a5cdd7 100644
> --- a/fs/xfs/xfs_buf.h
> +++ b/fs/xfs/xfs_buf.h
> @@ -298,8 +298,14 @@ extern void __xfs_buf_ioerror(struct xfs_buf *bp, int error,
>  		xfs_failaddr_t failaddr);
>  #define xfs_buf_ioerror(bp, err) __xfs_buf_ioerror((bp), (err), __this_address)
>  extern void xfs_buf_ioerror_alert(struct xfs_buf *, const char *func);
> -extern void xfs_buf_submit(struct xfs_buf *bp);
> -extern int xfs_buf_submit_wait(struct xfs_buf *bp);
> +
> +extern int __xfs_buf_submit(struct xfs_buf *bp, bool);
> +static inline int xfs_buf_submit(struct xfs_buf *bp)
> +{
> +	bool wait = bp->b_flags & XBF_ASYNC ? false : true;
> +	return __xfs_buf_submit(bp, wait);
> +}
> +
>  extern void xfs_buf_iomove(xfs_buf_t *, size_t, size_t, void *,
>  				xfs_buf_rw_t);
>  #define xfs_buf_zero(bp, off, len) \
> diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
> index b181b5f57a19..724a76d87564 100644
> --- a/fs/xfs/xfs_log_recover.c
> +++ b/fs/xfs/xfs_log_recover.c
> @@ -196,7 +196,7 @@ xlog_bread_noalign(
>  	bp->b_io_length = nbblks;
>  	bp->b_error = 0;
>  
> -	error = xfs_buf_submit_wait(bp);
> +	error = xfs_buf_submit(bp);
>  	if (error && !XFS_FORCED_SHUTDOWN(log->l_mp))
>  		xfs_buf_ioerror_alert(bp, __func__);
>  	return error;
> @@ -5707,7 +5707,7 @@ xlog_do_recover(
>  	bp->b_flags |= XBF_READ;
>  	bp->b_ops = &xfs_sb_buf_ops;
>  
> -	error = xfs_buf_submit_wait(bp);
> +	error = xfs_buf_submit(bp);
>  	if (error) {
>  		if (!XFS_FORCED_SHUTDOWN(mp)) {
>  			xfs_buf_ioerror_alert(bp, __func__);
> -- 
> 2.17.1
> 
> --
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Re: [PATCH 2/2] xfs: kill __xfs_buf_submit_common()

[Darrick J. Wong]

On Mon, Jun 18, 2018 at 10:52:44AM -0400, Brian Foster wrote:
> Now that there is only one caller, fold the common submission helper
> into __xfs_buf_submit().
> 
> Suggested-by: Christoph Hellwig <hch@infradead.org>
> Signed-off-by: Brian Foster <bfoster@redhat.com>

Looks ok enough to test,
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> ---
>  fs/xfs/xfs_buf.c | 83 ++++++++++++++++++++----------------------------
>  1 file changed, 34 insertions(+), 49 deletions(-)
> 
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index 64a9a09013e3..f747792038dc 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -1449,15 +1449,34 @@ _xfs_buf_ioapply(
>  }
>  
>  /*
> - * Asynchronous IO submission path. This transfers the buffer lock ownership and
> - * the current reference to the IO. It is not safe to reference the buffer after
> - * a call to this function unless the caller holds an additional reference
> - * itself.
> + * Wait for I/O completion of a sync buffer and return the I/O error code.
>   */
>  static int
> -__xfs_buf_submit_common(
> +xfs_buf_iowait(
>  	struct xfs_buf	*bp)
>  {
> +	ASSERT(!(bp->b_flags & XBF_ASYNC));
> +
> +	trace_xfs_buf_iowait(bp, _RET_IP_);
> +	wait_for_completion(&bp->b_iowait);
> +	trace_xfs_buf_iowait_done(bp, _RET_IP_);
> +
> +	return bp->b_error;
> +}
> +
> +/*
> + * Buffer I/O submission path, read or write. Asynchronous submission transfers
> + * the buffer lock ownership and the current reference to the IO. It is not
> + * safe to reference the buffer after a call to this function unless the caller
> + * holds an additional reference itself.
> + */
> +int
> +__xfs_buf_submit(
> +	struct xfs_buf	*bp,
> +	bool		wait)
> +{
> +	int		error = 0;
> +
>  	trace_xfs_buf_submit(bp, _RET_IP_);
>  
>  	ASSERT(!(bp->b_flags & _XBF_DELWRI_Q));
> @@ -1467,9 +1486,18 @@ __xfs_buf_submit_common(
>  		xfs_buf_ioerror(bp, -EIO);
>  		bp->b_flags &= ~XBF_DONE;
>  		xfs_buf_stale(bp);
> +		if (bp->b_flags & XBF_ASYNC)
> +			xfs_buf_ioend(bp);
>  		return -EIO;
>  	}
>  
> +	/*
> +	 * Grab a reference so the buffer does not go away underneath us. For
> +	 * async buffers, I/O completion drops the callers reference, which
> +	 * could occur before submission returns.
> +	 */
> +	xfs_buf_hold(bp);
> +
>  	if (bp->b_flags & XBF_WRITE)
>  		xfs_buf_wait_unpin(bp);
>  
> @@ -1498,52 +1526,9 @@ __xfs_buf_submit_common(
>  			xfs_buf_ioend_async(bp);
>  	}
>  
> -	return 0;
> -}
> -
> -/*
> - * Wait for I/O completion of a sync buffer and return the I/O error code.
> - */
> -static int
> -xfs_buf_iowait(
> -	struct xfs_buf	*bp)
> -{
> -	ASSERT(!(bp->b_flags & XBF_ASYNC));
> -
> -	trace_xfs_buf_iowait(bp, _RET_IP_);
> -	wait_for_completion(&bp->b_iowait);
> -	trace_xfs_buf_iowait_done(bp, _RET_IP_);
> -
> -	return bp->b_error;
> -}
> -
> -/*
> - * Synchronous buffer IO submission path, read or write.
> - */
> -int
> -__xfs_buf_submit(
> -	struct xfs_buf	*bp,
> -	bool		wait)
> -{
> -	int		error;
> -
> -	/*
> -	 * Grab a reference so the buffer does not go away underneath us. For
> -	 * async buffers, I/O completion drops the callers reference, which
> -	 * could occur before submission returns.
> -	 */
> -	xfs_buf_hold(bp);
> -
> -	error = __xfs_buf_submit_common(bp);
> -	if (error) {
> -		if (bp->b_flags & XBF_ASYNC)
> -			xfs_buf_ioend(bp);
> -		goto out;
> -	}
> -
>  	if (wait)
>  		error = xfs_buf_iowait(bp);
> -out:
> +
>  	/*
>  	 * Release the hold that keeps the buffer referenced for the entire
>  	 * I/O. Note that if the buffer is async, it is not safe to reference
> -- 
> 2.17.1
> 
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Re: [PATCH 1/2] xfs: combine [a]sync buffer submission apis

[Christoph Hellwig]

On Mon, Jun 18, 2018 at 10:52:43AM -0400, Brian Foster wrote:
> The buffer I/O submission path consists of separate function calls
> per type. The buffer I/O type is already controlled via buffer
> state (XBF_ASYNC), however, so there is no real need for separate
> submission functions.
> 
> Combine the buffer submission functions into a single function that
> processes the buffer appropriately based on XBF_ASYNC. Retain an
> internal helper with a conditional wait parameter to continue to
> support batched !XBF_ASYNC submission/completion required by delwri
> queues.
> 
> Suggested-by: Christoph Hellwig <hch@infradead.org>
> Signed-off-by: Brian Foster <bfoster@redhat.com>

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH 2/2] xfs: kill __xfs_buf_submit_common()

[Christoph Hellwig]

On Mon, Jun 18, 2018 at 10:52:44AM -0400, Brian Foster wrote:
> Now that there is only one caller, fold the common submission helper
> into __xfs_buf_submit().
> 
> Suggested-by: Christoph Hellwig <hch@infradead.org>
> Signed-off-by: Brian Foster <bfoster@redhat.com>

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>