xfs: only grab shared inode locks for source file during reflink

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>

diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index bcc58c2..85a119e 100644 (file)
--- 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 @@ retry:
        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 @@ retry:
        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 7f8d96d..5cbeab8 100644 (file)
--- 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*);