On Thu, Aug 27, 2015 at 6:48 AM, Dave Chinner [off-list ref] wrote:

On Wed, Aug 26, 2015 at 04:16:46PM +0800, Peng Tao wrote:

quoted

Signed-off-by: Peng Tao <redacted>
---
 fs/nfs/nfs4file.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)

diff --git a/fs/nfs/nfs4file.c b/fs/nfs/nfs4file.c
index dcd39d4..c335cb0 100644
--- a/fs/nfs/nfs4file.c
+++ b/fs/nfs/nfs4file.c

@@ -4,6 +4,7 @@
  *  Copyright (C) 1992  Rick Sladkey
  */
 #include <linux/fs.h>
+#include <linux/file.h>
 #include <linux/falloc.h>
 #include <linux/nfs_fs.h>
 #include "internal.h"

@@ -166,6 +167,54 @@ static long nfs42_fallocate(struct file *filep, int mode, loff_t offset, loff_t
              return nfs42_proc_deallocate(filep, offset, len);
      return nfs42_proc_allocate(filep, offset, len);
 }
+
+static noinline int
+nfs42_file_clone_range(struct file *src_file, struct file *dst_file,
+                    loff_t src_off, size_t dst_off, loff_t count)
+{
+     struct inode *dst_inode = file_inode(dst_file);
+     struct inode *src_inode = file_inode(src_file);
+     int ret;
+
+     /* src and dst must be different files */
+     if (src_inode == dst_inode)
+             return -EINVAL;
+
+     /* XXX: do we lock at all? what if server needs CB_RECALL_LAYOUT? */
+     if (dst_inode < src_inode) {
+             mutex_lock_nested(&dst_inode->i_mutex, I_MUTEX_PARENT);
+             mutex_lock_nested(&src_inode->i_mutex, I_MUTEX_CHILD);
+     } else {
+             mutex_lock_nested(&src_inode->i_mutex, I_MUTEX_PARENT);
+             mutex_lock_nested(&dst_inode->i_mutex, I_MUTEX_CHILD);
+     }

Is that safe? Between two operations, the inode code be reclaimed
and re-instantiated, resulting in the second operation having a
different locking order for the same files compared to the
first operation...

Both files are still open so I don't think we need to worry about
inode going away.

quoted

+out_unlock:
+     if (dst_inode < src_inode) {
+             mutex_unlock(&src_inode->i_mutex);
+             mutex_unlock(&dst_inode->i_mutex);
+     } else {
+             mutex_unlock(&dst_inode->i_mutex);
+             mutex_unlock(&src_inode->i_mutex);
+     }

You don't have to care about lock order on unlock.

Good point!

Thanks,
Tao