f2fs: use shared inode lock during f2fs_fiemap()

f2fs_fiemap() will only traverse metadata of inode, let's use shared
inode lock for it to avoid unnecessary race on inode lock.
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -1992,7 +1992,7 @@ int f2fs_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 	if (ret)
 		return ret;
 
-	inode_lock(inode);
+	inode_lock_shared(inode);
 
 	maxbytes = max_file_blocks(inode) << F2FS_BLKSIZE_BITS;
 	if (start > maxbytes) {
@@ -2112,7 +2112,7 @@ int f2fs_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 	if (ret == 1)
 		ret = 0;
 
-	inode_unlock(inode);
+	inode_unlock_shared(inode);
 	return ret;
 }