[PATCH 2/6] xfs: only grab shared inode locks for source file during reflink

["Darrick J. Wong" <darrick.wong@xxxxxxxxxx>]

From: Darrick J. Wong <darrick.wong@xxxxxxxxxx>

Reflink and dedupe operations remap blocks from a source file into a
destination file.  The destination file needs exclusive locks on all
levels because we're updating its block map, but the source file isn't
undergoing any block map changes so we can use a shared lock.

Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
---
 fs/xfs/xfs_reflink.c |   50 +++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 37 insertions(+), 13 deletions(-)


diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index ce523dd..5d1ff5a 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -1202,13 +1202,16 @@ xfs_reflink_remap_blocks(
 
 	/* drange = (destoff, destoff + len); srange = (srcoff, srcoff + len) */
 	while (len) {
+		uint		lock_mode;
+
 		trace_xfs_reflink_remap_blocks_loop(src, srcoff, len,
 				dest, destoff);
+
 		/* Read extent from the source file */
 		nimaps = 1;
-		xfs_ilock(src, XFS_ILOCK_EXCL);
+		lock_mode = xfs_ilock_data_map_shared(src);
 		error = xfs_bmapi_read(src, srcoff, len, &imap, &nimaps, 0);
-		xfs_iunlock(src, XFS_ILOCK_EXCL);
+		xfs_iunlock(src, lock_mode);
 		if (error)
 			goto err;
 		ASSERT(nimaps == 1);
@@ -1260,7 +1263,7 @@ xfs_iolock_two_inodes_and_break_layout(
 
 retry:
 	if (src_first) {
-		inode_lock(src);
+		inode_lock_shared(src);
 		inode_lock_nested(dest, I_MUTEX_NONDIR2);
 	} else {
 		inode_lock(dest);
@@ -1270,7 +1273,7 @@ xfs_iolock_two_inodes_and_break_layout(
 	if (error == -EWOULDBLOCK) {
 		inode_unlock(dest);
 		if (src_first)
-			inode_unlock(src);
+			inode_unlock_shared(src);
 		error = break_layout(dest, true);
 		if (error)
 			return error;
@@ -1278,14 +1281,36 @@ xfs_iolock_two_inodes_and_break_layout(
 	} else if (error) {
 		inode_unlock(dest);
 		if (src_first)
-			inode_unlock(src);
+			inode_unlock_shared(src);
 		return error;
 	}
 	if (src_last)
-		inode_lock_nested(src, I_MUTEX_NONDIR2);
+		down_read_nested(&src->i_rwsem, I_MUTEX_NONDIR2);
 	return 0;
 }
 
+static void
+xfs_reflink_mmaplock_two(
+	struct xfs_inode	*src,
+	struct xfs_inode	*dest)
+{
+	int			i = 0;
+
+	if (src->i_ino == dest->i_ino) {
+		xfs_ilock(src, XFS_MMAPLOCK_EXCL);
+		return;
+	}
+
+	if (src->i_ino < dest->i_ino) {
+		xfs_ilock(src, XFS_MMAPLOCK_SHARED);
+		i++;
+	}
+	xfs_ilock(dest, XFS_MMAPLOCK_EXCL + (i << XFS_MMAPLOCK_SHIFT));
+	i++;
+	if (src->i_ino > dest->i_ino)
+		xfs_ilock(src, XFS_MMAPLOCK_SHARED + (i << XFS_MMAPLOCK_SHIFT));
+}
+
 /*
  * Link a range of blocks from one file to another.
  */
@@ -1319,10 +1344,7 @@ xfs_reflink_remap_range(
 	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
-		xfs_lock_two_inodes(src, dest, XFS_MMAPLOCK_EXCL);
+	xfs_reflink_mmaplock_two(src, dest);
 
 	/* Check file eligibility and prepare for block sharing. */
 	ret = -EINVAL;
@@ -1385,10 +1407,12 @@ xfs_reflink_remap_range(
 			is_dedupe);
 
 out_unlock:
-	xfs_iunlock(src, XFS_MMAPLOCK_EXCL);
+	xfs_iunlock(dest, XFS_MMAPLOCK_EXCL);
+	if (!same_inode)
+		xfs_iunlock(src, XFS_MMAPLOCK_SHARED);
+	inode_unlock(inode_out);
 	if (!same_inode)
-		xfs_iunlock(dest, XFS_MMAPLOCK_EXCL);
-	unlock_two_nondirectories(inode_in, inode_out);
+		inode_unlock_shared(inode_in);
 	if (ret)
 		trace_xfs_reflink_remap_range_error(dest, ret, _RET_IP_);
 	return ret;

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