xfs: add the ability to join a held buffer to a defer_ops

In certain cases, defer_ops callers will lock a buffer and want to hold
the lock across transaction rolls.  Similar to ijoined inodes, we want
to dirty & join the buffer with each transaction roll in defer_finish so
that afterwards the caller still owns the buffer lock and we haven't
inadvertently pinned the log.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

1 files changed, 36 insertions, 3 deletions

diff --git a/fs/xfs/libxfs/xfs_defer.c b/fs/xfs/libxfs/xfs_defer.c
index 072ebfe1d6ae..087fea02c389 100644
--- a/fs/xfs/libxfs/xfs_defer.c
+++ b/fs/xfs/libxfs/xfs_defer.c
@@ -249,6 +249,10 @@ xfs_defer_trans_roll(
 	for (i = 0; i < XFS_DEFER_OPS_NR_INODES && dop->dop_inodes[i]; i++)
 		xfs_trans_log_inode(*tp, dop->dop_inodes[i], XFS_ILOG_CORE);
 
+	/* Hold the (previously bjoin'd) buffer locked across the roll. */
+	for (i = 0; i < XFS_DEFER_OPS_NR_BUFS && dop->dop_bufs[i]; i++)
+		xfs_trans_dirty_buf(*tp, dop->dop_bufs[i]);
+
 	trace_xfs_defer_trans_roll((*tp)->t_mountp, dop);
 
 	/* Roll the transaction. */
@@ -264,6 +268,12 @@ xfs_defer_trans_roll(
 	for (i = 0; i < XFS_DEFER_OPS_NR_INODES && dop->dop_inodes[i]; i++)
 		xfs_trans_ijoin(*tp, dop->dop_inodes[i], 0);
 
+	/* Rejoin the buffers and dirty them so the log moves forward. */
+	for (i = 0; i < XFS_DEFER_OPS_NR_BUFS && dop->dop_bufs[i]; i++) {
+		xfs_trans_bjoin(*tp, dop->dop_bufs[i]);
+		xfs_trans_bhold(*tp, dop->dop_bufs[i]);
+	}
+
 	return error;
 }
 
@@ -295,6 +305,31 @@ xfs_defer_ijoin(
 		}
 	}
 
+	ASSERT(0);
+	return -EFSCORRUPTED;
+}
+
+/*
+ * Add this buffer to the deferred op.  Each joined buffer is relogged
+ * each time we roll the transaction.
+ */
+int
+xfs_defer_bjoin(
+	struct xfs_defer_ops		*dop,
+	struct xfs_buf			*bp)
+{
+	int				i;
+
+	for (i = 0; i < XFS_DEFER_OPS_NR_BUFS; i++) {
+		if (dop->dop_bufs[i] == bp)
+			return 0;
+		else if (dop->dop_bufs[i] == NULL) {
+			dop->dop_bufs[i] = bp;
+			return 0;
+		}
+	}
+
+	ASSERT(0);
 	return -EFSCORRUPTED;
 }
 
@@ -493,9 +528,7 @@ xfs_defer_init(
 	struct xfs_defer_ops		*dop,
 	xfs_fsblock_t			*fbp)
 {
-	dop->dop_committed = false;
-	dop->dop_low = false;
-	memset(&dop->dop_inodes, 0, sizeof(dop->dop_inodes));
+	memset(dop, 0, sizeof(struct xfs_defer_ops));
 	*fbp = NULLFSBLOCK;
 	INIT_LIST_HEAD(&dop->dop_intake);
 	INIT_LIST_HEAD(&dop->dop_pending);