[PATCH v3 09/12] fs/xfs: Add write DAX lock to xfs layer

[ira.weiny@intel.com]

From: Ira Weiny <ira.weiny@intel.com>

XFS requires regular files to be locked for write while changing to/from
DAX state.

Take the DAX write lock while changing DAX state.

We define a new XFS_DAX_EXCL lock type to carry the lock through to
transaction completion.

Signed-off-by: Ira Weiny <ira.weiny@intel.com>

---
Changes from V2:
	Change name of patch (WAS: fs/xfs: Add lock/unlock state to xfs)
	Remove the xfs specific lock and move to the vfs layer.
		We still use XFS_LOCK_DAX_EXCL to be able to pass this
		flag through to the transaction code.  But we no longer
		have a lock specific to xfs.  This removes a lot of code
		from the XFS layer, preps us for using this in ext4, and
		is actually more straight forward now that all the
		locking requirements are better known.

	Fix locking order comment
	Rework for new 'state' names
	(Other comments on the previous patch are not applicable with
	new patch as much of the code was removed in favor of the vfs
	level lock)

 fs/xfs/xfs_inode.c | 22 ++++++++++++++++++++--
 fs/xfs/xfs_inode.h |  7 +++++--
 2 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index 35df324875db..0c7b1855e0c8 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -142,12 +142,12 @@ xfs_ilock_attr_map_shared(
  *
  * Basic locking order:
  *
- * i_rwsem -> i_mmap_lock -> page_lock -> i_ilock
+ * s_dax_sem -> i_rwsem -> i_mmap_lock -> page_lock -> i_ilock
  *
  * mmap_sem locking order:
  *
  * i_rwsem -> page lock -> mmap_sem
- * mmap_sem -> i_mmap_lock -> page_lock
+ * s_dax_sem -> mmap_sem -> i_mmap_lock -> page_lock
  *
  * The difference in mmap_sem locking order mean that we cannot hold the
  * i_mmap_lock over syscall based read(2)/write(2) based IO. These IO paths can
@@ -182,6 +182,9 @@ xfs_ilock(
 	       (XFS_ILOCK_SHARED | XFS_ILOCK_EXCL));
 	ASSERT((lock_flags & ~(XFS_LOCK_MASK | XFS_LOCK_SUBCLASS_MASK)) == 0);
 
+	if (lock_flags & XFS_DAX_EXCL)
+		inode_dax_state_down_write(VFS_I(ip));
+
 	if (lock_flags & XFS_IOLOCK_EXCL) {
 		down_write_nested(&VFS_I(ip)->i_rwsem,
 				  XFS_IOLOCK_DEP(lock_flags));
@@ -224,6 +227,8 @@ xfs_ilock_nowait(
 	 * You can't set both SHARED and EXCL for the same lock,
 	 * and only XFS_IOLOCK_SHARED, XFS_IOLOCK_EXCL, XFS_ILOCK_SHARED,
 	 * and XFS_ILOCK_EXCL are valid values to set in lock_flags.
+	 *
+	 * XFS_DAX_* is not allowed
 	 */
 	ASSERT((lock_flags & (XFS_IOLOCK_SHARED | XFS_IOLOCK_EXCL)) !=
 	       (XFS_IOLOCK_SHARED | XFS_IOLOCK_EXCL));
@@ -232,6 +237,7 @@ xfs_ilock_nowait(
 	ASSERT((lock_flags & (XFS_ILOCK_SHARED | XFS_ILOCK_EXCL)) !=
 	       (XFS_ILOCK_SHARED | XFS_ILOCK_EXCL));
 	ASSERT((lock_flags & ~(XFS_LOCK_MASK | XFS_LOCK_SUBCLASS_MASK)) == 0);
+	ASSERT((lock_flags & XFS_DAX_EXCL) == 0);
 
 	if (lock_flags & XFS_IOLOCK_EXCL) {
 		if (!down_write_trylock(&VFS_I(ip)->i_rwsem))
@@ -318,6 +324,9 @@ xfs_iunlock(
 	else if (lock_flags & XFS_ILOCK_SHARED)
 		mrunlock_shared(&ip->i_lock);
 
+	if (lock_flags & XFS_DAX_EXCL)
+		inode_dax_state_up_write(VFS_I(ip));
+
 	trace_xfs_iunlock(ip, lock_flags, _RET_IP_);
 }
 
@@ -333,6 +342,8 @@ xfs_ilock_demote(
 	ASSERT(lock_flags & (XFS_IOLOCK_EXCL|XFS_MMAPLOCK_EXCL|XFS_ILOCK_EXCL));
 	ASSERT((lock_flags &
 		~(XFS_IOLOCK_EXCL|XFS_MMAPLOCK_EXCL|XFS_ILOCK_EXCL)) == 0);
+	/* XFS_DAX_* is not allowed */
+	ASSERT((lock_flags & XFS_DAX_EXCL) == 0);
 
 	if (lock_flags & XFS_ILOCK_EXCL)
 		mrdemote(&ip->i_lock);
@@ -465,6 +476,9 @@ xfs_lock_inodes(
 	ASSERT(!(lock_mode & XFS_ILOCK_EXCL) ||
 		inodes <= XFS_ILOCK_MAX_SUBCLASS + 1);
 
+	/* XFS_DAX_* is not allowed */
+	ASSERT((lock_mode & XFS_DAX_EXCL) == 0);
+
 	if (lock_mode & XFS_IOLOCK_EXCL) {
 		ASSERT(!(lock_mode & (XFS_MMAPLOCK_EXCL | XFS_ILOCK_EXCL)));
 	} else if (lock_mode & XFS_MMAPLOCK_EXCL)
@@ -566,6 +580,10 @@ xfs_lock_two_inodes(
 	ASSERT(!(ip0_mode & (XFS_MMAPLOCK_SHARED|XFS_MMAPLOCK_EXCL)) ||
 	       !(ip1_mode & (XFS_ILOCK_SHARED|XFS_ILOCK_EXCL)));
 
+	/* XFS_DAX_* is not allowed */
+	ASSERT((ip0_mode & XFS_DAX_EXCL) == 0);
+	ASSERT((ip1_mode & XFS_DAX_EXCL) == 0);
+
 	ASSERT(ip0->i_ino != ip1->i_ino);
 
 	if (ip0->i_ino > ip1->i_ino) {
diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
index 492e53992fa9..25fe20740bf7 100644
--- a/fs/xfs/xfs_inode.h
+++ b/fs/xfs/xfs_inode.h
@@ -278,10 +278,12 @@ static inline void xfs_ifunlock(struct xfs_inode *ip)
 #define	XFS_ILOCK_SHARED	(1<<3)
 #define	XFS_MMAPLOCK_EXCL	(1<<4)
 #define	XFS_MMAPLOCK_SHARED	(1<<5)
+#define	XFS_DAX_EXCL		(1<<6)
 
 #define XFS_LOCK_MASK		(XFS_IOLOCK_EXCL | XFS_IOLOCK_SHARED \
 				| XFS_ILOCK_EXCL | XFS_ILOCK_SHARED \
-				| XFS_MMAPLOCK_EXCL | XFS_MMAPLOCK_SHARED)
+				| XFS_MMAPLOCK_EXCL | XFS_MMAPLOCK_SHARED \
+				| XFS_DAX_EXCL)
 
 #define XFS_LOCK_FLAGS \
 	{ XFS_IOLOCK_EXCL,	"IOLOCK_EXCL" }, \
@@ -289,7 +291,8 @@ static inline void xfs_ifunlock(struct xfs_inode *ip)
 	{ XFS_ILOCK_EXCL,	"ILOCK_EXCL" }, \
 	{ XFS_ILOCK_SHARED,	"ILOCK_SHARED" }, \
 	{ XFS_MMAPLOCK_EXCL,	"MMAPLOCK_EXCL" }, \
-	{ XFS_MMAPLOCK_SHARED,	"MMAPLOCK_SHARED" }
+	{ XFS_MMAPLOCK_SHARED,	"MMAPLOCK_SHARED" }, \
+	{ XFS_DAX_EXCL,		"DAX_EXCL" }
 
 
 /*
-- 
2.21.0