[PATCH 2/4] libxfs: fix buffer refcounting in delwri_queue

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

From: Darrick J. Wong <darrick.wong@oracle.com>

In the kernel, xfs_buf_delwri_queue increments the buffer reference
count before putting the buffer on the buffer list, and the refcount is
decremented after the io completes for a net refcount change of zero.

In userspace, delwri_queue calls libxfs_writebuf, which puts the buffer.
delwri_queue is a no-op, for a net refcount change of -1.  This creates
problems for any callers that expect a net change of zero, so increment
the buffer refcount before calling writebuf.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 libxfs/libxfs_io.h   |    7 +++++++
 libxfs/libxfs_priv.h |    1 -
 2 files changed, 7 insertions(+), 1 deletion(-)


diff --git a/libxfs/libxfs_io.h b/libxfs/libxfs_io.h
index 7dcb4bff..09ed043b 100644
--- a/libxfs/libxfs_io.h
+++ b/libxfs/libxfs_io.h
@@ -245,4 +245,11 @@ xfs_buf_get_uncached(struct xfs_buftarg *targ, size_t bblen, int flags)
 	return bp;
 }
 
+static inline void
+xfs_buf_delwri_queue(struct xfs_buf *bp, struct list_head *buffer_list)
+{
+	bp->b_node.cn_count++;
+	libxfs_writebuf(bp, 0);
+}
+
 #endif	/* __LIBXFS_IO_H__ */
diff --git a/libxfs/libxfs_priv.h b/libxfs/libxfs_priv.h
index b05e082a..13dab58a 100644
--- a/libxfs/libxfs_priv.h
+++ b/libxfs/libxfs_priv.h
@@ -382,7 +382,6 @@ roundup_64(uint64_t x, uint32_t y)
 #define xfs_buf_relse(bp)		libxfs_putbuf(bp)
 #define xfs_buf_get(devp,blkno,len)	(libxfs_getbuf((devp), (blkno), (len)))
 #define xfs_bwrite(bp)			libxfs_writebuf((bp), 0)
-#define xfs_buf_delwri_queue(bp, bl)	libxfs_writebuf((bp), 0)
 #define xfs_buf_delwri_submit(bl)	(0)
 #define xfs_buf_oneshot(bp)		((void) 0)