From 1364b1d4b5df31a05b6a3e6fdeb5371dbd4bd8ac Mon Sep 17 00:00:00 2001
From: "Darrick J. Wong" <darrick.wong@oracle.com>
Date: Thu, 18 Jan 2018 13:55:20 -0800
Subject: [PATCH] xfs: reflink should break pnfs leases before sharing blocks
Git-commit: 1364b1d4b5df31a05b6a3e6fdeb5371dbd4bd8ac
Patch-mainline: v4.16-rc1
References: bsc#1132369, bsc#1132219

Before we share blocks between files, we need to break the pnfs leases
on the layout before we start slicing and dicing the block map.  The
structure of this function sets us up for the lock contention reduction
in the next patch.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Anthony Iliopoulos <ailiopoulos@suse.com>

---
 fs/xfs/xfs_reflink.c | 48 +++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 47 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index bcc2ad4f0899..bac464f0bc59 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -1244,6 +1244,50 @@ xfs_reflink_remap_blocks(
 	return error;
 }
 
+/*
+ * Grab the exclusive iolock for a data copy from src to dest, making
+ * sure to abide vfs locking order (lowest pointer value goes first) and
+ * breaking the pnfs layout leases on dest before proceeding.  The loop
+ * is needed because we cannot call the blocking break_layout() with the
+ * src iolock held, and therefore have to back out both locks.
+ */
+static int
+xfs_iolock_two_inodes_and_break_layout(
+	struct inode		*src,
+	struct inode		*dest)
+{
+	int			error;
+
+retry:
+	if (src < dest) {
+		inode_lock(src);
+		inode_lock_nested(dest, I_MUTEX_NONDIR2);
+	} else {
+		/* src >= dest */
+		inode_lock(dest);
+	}
+
+	error = break_layout(dest, false);
+	if (error == -EWOULDBLOCK) {
+		inode_unlock(dest);
+		if (src < dest)
+			inode_unlock(src);
+		error = break_layout(dest, true);
+		if (error)
+			return error;
+		goto retry;
+	}
+	if (error) {
+		inode_unlock(dest);
+		if (src < dest)
+			inode_unlock(src);
+		return error;
+	}
+	if (src > dest)
+		inode_lock_nested(src, I_MUTEX_NONDIR2);
+	return 0;
+}
+
 /*
  * Link a range of blocks from one file to another.
  */
@@ -1274,7 +1318,9 @@ xfs_reflink_remap_range(
 		return -EIO;
 
 	/* Lock both files against IO */
-	lock_two_nondirectories(inode_in, inode_out);
+	ret = xfs_iolock_two_inodes_and_break_layout(inode_in, inode_out);
+	if (ret)
+		return ret;
 	if (same_inode)
 		xfs_ilock(src, XFS_MMAPLOCK_EXCL);
 	else
-- 
2.16.4