From 01c2e13dcae9757ea987af8933f9fcc6e33f2d7c Mon Sep 17 00:00:00 2001
From: "Darrick J. Wong" <darrick.wong@oracle.com>
Date: Thu, 18 Jan 2018 14:07:53 -0800
Subject: [PATCH] xfs: only grab shared inode locks for source file during
 reflink
Git-commit: 01c2e13dcae9757ea987af8933f9fcc6e33f2d7c
Patch-mainline: v4.16-rc1
References: bsc#1132372, bsc#1132219

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@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Anthony Iliopoulos <ailiopoulos@suse.com>

---
 fs/xfs/xfs_reflink.c | 25 +++++++++++++++----------
 include/linux/fs.h   |  5 +++++
 2 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index bcc58c24287c..85a119e1463b 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 < dest) {
-		inode_lock(src);
+		inode_lock_shared(src);
 		inode_lock_nested(dest, I_MUTEX_NONDIR2);
 	} else {
 		/* src >= dest */
@@ -1271,7 +1274,7 @@ xfs_iolock_two_inodes_and_break_layout(
 	if (error == -EWOULDBLOCK) {
 		inode_unlock(dest);
 		if (src < dest)
-			inode_unlock(src);
+			inode_unlock_shared(src);
 		error = break_layout(dest, true);
 		if (error)
 			return error;
@@ -1280,11 +1283,11 @@ xfs_iolock_two_inodes_and_break_layout(
 	if (error) {
 		inode_unlock(dest);
 		if (src < dest)
-			inode_unlock(src);
+			inode_unlock_shared(src);
 		return error;
 	}
 	if (src > dest)
-		inode_lock_nested(src, I_MUTEX_NONDIR2);
+		inode_lock_shared_nested(src, I_MUTEX_NONDIR2);
 	return 0;
 }
 
@@ -1324,7 +1327,7 @@ xfs_reflink_remap_range(
 	if (same_inode)
 		xfs_ilock(src, XFS_MMAPLOCK_EXCL);
 	else
-		xfs_lock_two_inodes(src, XFS_MMAPLOCK_EXCL, dest,
+		xfs_lock_two_inodes(src, XFS_MMAPLOCK_SHARED, dest,
 				XFS_MMAPLOCK_EXCL);
 
 	/* Check file eligibility and prepare for block sharing. */
@@ -1393,10 +1396,12 @@ 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;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 7f8d96d68f34..5cbeab8a63ca 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -748,6 +748,11 @@ static inline void inode_lock_nested(struct inode *inode, unsigned subclass)
 	down_write_nested(&inode->i_rwsem, subclass);
 }
 
+static inline void inode_lock_shared_nested(struct inode *inode, unsigned subclass)
+{
+	down_read_nested(&inode->i_rwsem, subclass);
+}
+
 void lock_two_nondirectories(struct inode *, struct inode*);
 void unlock_two_nondirectories(struct inode *, struct inode*);
 
-- 
2.16.4