[PATCH 02/12] xfs: factor out buffer I/O failure simulation code

[Brian Foster <bfoster@redhat.com>]

We use the same buffer I/O failure simulation code in a few
different places. It's not much code, but it's not necessarily
self-explanatory. Factor it into a helper and document it in one
place.

Signed-off-by: Brian Foster <bfoster@redhat.com>
---
 fs/xfs/xfs_buf.c      | 23 +++++++++++++++++++----
 fs/xfs/xfs_buf.h      |  1 +
 fs/xfs/xfs_buf_item.c | 22 +++-------------------
 fs/xfs/xfs_inode.c    |  7 +------
 4 files changed, 24 insertions(+), 29 deletions(-)

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 9ec3eaf1c618..93942d8e35dd 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -1248,6 +1248,24 @@ xfs_buf_ioerror_alert(
 			-bp->b_error);
 }
 
+/*
+  * To simulate an I/O failure, the buffer must be locked and held with at least
+ * three references. The LRU reference is dropped by the stale call. The buf
+ * item reference is dropped via ioend processing. The third reference is owned
+ * by the caller and is dropped on I/O completion if the buffer is XBF_ASYNC.
+ */
+void
+xfs_buf_iofail(
+	struct xfs_buf	*bp,
+	int		flags)
+{
+	bp->b_flags |= flags;
+	bp->b_flags &= ~XBF_DONE;
+	xfs_buf_stale(bp);
+	xfs_buf_ioerror(bp, -EIO);
+	xfs_buf_ioend(bp);
+}
+
 int
 xfs_bwrite(
 	struct xfs_buf		*bp)
@@ -1480,10 +1498,7 @@ __xfs_buf_submit(
 
 	/* on shutdown we stale and complete the buffer immediately */
 	if (XFS_FORCED_SHUTDOWN(bp->b_mount)) {
-		xfs_buf_ioerror(bp, -EIO);
-		bp->b_flags &= ~XBF_DONE;
-		xfs_buf_stale(bp);
-		xfs_buf_ioend(bp);
+		xfs_buf_iofail(bp, 0);
 		return -EIO;
 	}
 
diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
index 9a04c53c2488..a6bce4702b2e 100644
--- a/fs/xfs/xfs_buf.h
+++ b/fs/xfs/xfs_buf.h
@@ -263,6 +263,7 @@ 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 *bp, xfs_failaddr_t fa);
+void xfs_buf_iofail(struct xfs_buf *, int);
 
 extern int __xfs_buf_submit(struct xfs_buf *bp, bool);
 static inline int xfs_buf_submit(struct xfs_buf *bp)
diff --git a/fs/xfs/xfs_buf_item.c b/fs/xfs/xfs_buf_item.c
index 8796adde2d12..72d37a4609d8 100644
--- a/fs/xfs/xfs_buf_item.c
+++ b/fs/xfs/xfs_buf_item.c
@@ -471,28 +471,12 @@ xfs_buf_item_unpin(
 		xfs_buf_relse(bp);
 	} else if (freed && remove) {
 		/*
-		 * There are currently two references to the buffer - the active
-		 * LRU reference and the buf log item. What we are about to do
-		 * here - simulate a failed IO completion - requires 3
-		 * references.
-		 *
-		 * The LRU reference is removed by the xfs_buf_stale() call. The
-		 * buf item reference is removed by the xfs_buf_iodone()
-		 * callback that is run by xfs_buf_do_callbacks() during ioend
-		 * processing (via the bp->b_iodone callback), and then finally
-		 * the ioend processing will drop the IO reference if the buffer
-		 * is marked XBF_ASYNC.
-		 *
-		 * Hence we need to take an additional reference here so that IO
-		 * completion processing doesn't free the buffer prematurely.
+		 * The buffer must be locked and held by the caller to simulate
+		 * an async I/O failure.
 		 */
 		xfs_buf_lock(bp);
 		xfs_buf_hold(bp);
-		bp->b_flags |= XBF_ASYNC;
-		xfs_buf_ioerror(bp, -EIO);
-		bp->b_flags &= ~XBF_DONE;
-		xfs_buf_stale(bp);
-		xfs_buf_ioend(bp);
+		xfs_buf_iofail(bp, XBF_ASYNC);
 	}
 }
 
diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index d1772786af29..b539ee221ce5 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -3629,12 +3629,7 @@ xfs_iflush_cluster(
 	 * xfs_buf_submit().
 	 */
 	ASSERT(bp->b_iodone);
-	bp->b_flags |= XBF_ASYNC;
-	bp->b_flags &= ~XBF_DONE;
-	xfs_buf_stale(bp);
-	xfs_buf_ioerror(bp, -EIO);
-	xfs_buf_ioend(bp);
-
+	xfs_buf_iofail(bp, XBF_ASYNC);
 	xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
 
 	/* abort the corrupt inode, as it was not attached to the buffer */
-- 
2.21.1