xfs: prepare xfs_break_layouts() for another layout type

When xfs is operating as the back-end of a pNFS block server, it
prevents collisions between local and remote operations by requiring a
lease to be held for remotely accessed blocks. Local filesystem
operations break those leases before writing or mutating the extent map
of the file.

A similar mechanism is needed to prevent operations on pinned dax
mappings, like device-DMA, from colliding with extent unmap operations.

BREAK_WRITE and BREAK_UNMAP are introduced as two distinct levels of
layout breaking.

Layouts are broken in the BREAK_WRITE case to ensure that layout-holders
do not collide with local writes. Additionally, layouts are broken in
the BREAK_UNMAP case to make sure the layout-holder has a consistent
view of the file's extent map. While BREAK_WRITE breaks can be satisfied
be recalling FL_LAYOUT leases, BREAK_UNMAP breaks additionally require
waiting for busy dax-pages to go idle while holding XFS_MMAPLOCK_EXCL.

After this refactoring xfs_break_layouts() becomes the entry point for
coordinating both types of breaks. Finally, xfs_break_leased_layouts()
becomes just the BREAK_WRITE handler.

Note that the unlock tracking is needed in a follow on change. That will
coordinate retrying either break handler until both successfully test
for a lease break while maintaining the lock state.

Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: "Darrick J. Wong" <darrick.wong@oracle.com>
Reported-by: Dave Chinner <david@fromorbit.com>
Reported-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 6 insertions, 6 deletions

diff --git a/fs/xfs/xfs_pnfs.c b/fs/xfs/xfs_pnfs.c
index 6ea7b0b55d02..f44c3599527d 100644
--- a/fs/xfs/xfs_pnfs.c
+++ b/fs/xfs/xfs_pnfs.c
@@ -31,17 +31,17 @@
  * rules in the page fault path we don't bother.
  */
 int
-xfs_break_layouts(
+xfs_break_leased_layouts(
 	struct inode		*inode,
-	uint			*iolock)
+	uint			*iolock,
+	bool			*did_unlock)
 {
 	struct xfs_inode	*ip = XFS_I(inode);
 	int			error;
 
-	ASSERT(xfs_isilocked(ip, XFS_IOLOCK_SHARED|XFS_IOLOCK_EXCL));
-
 	while ((error = break_layout(inode, false) == -EWOULDBLOCK)) {
 		xfs_iunlock(ip, *iolock);
+		*did_unlock = true;
 		error = break_layout(inode, true);
 		*iolock &= ~XFS_IOLOCK_SHARED;
 		*iolock |= XFS_IOLOCK_EXCL;
@@ -121,8 +121,8 @@ xfs_fs_map_blocks(
 	 * Lock out any other I/O before we flush and invalidate the pagecache,
 	 * and then hand out a layout to the remote system.  This is very
 	 * similar to direct I/O, except that the synchronization is much more
-	 * complicated.  See the comment near xfs_break_layouts for a detailed
-	 * explanation.
+	 * complicated.  See the comment near xfs_break_leased_layouts
+	 * for a detailed explanation.
 	 */
 	xfs_ilock(ip, XFS_IOLOCK_EXCL);