By general rule of thumb there shouldn't be any way that user land
could trigger a kernel operation just by sending wrong arguments.

Here do commit cleanups after user input has been verified.

Signed-off-by: Anand Jain <anand.j...@oracle.com>
---
 fs/btrfs/dev-replace.c | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index 673a2c3..937e53b 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -325,19 +325,6 @@ int btrfs_dev_replace_start(struct btrfs_root *root,
            args->start.tgtdev_name[0] == '\0')
                return -EINVAL;
 
-       /*
-        * Here we commit the transaction to make sure commit_total_bytes
-        * of all the devices are updated.
-        */
-       trans = btrfs_attach_transaction(root);
-       if (!IS_ERR(trans)) {
-               ret = btrfs_commit_transaction(trans, root);
-               if (ret)
-                       return ret;
-       } else if (PTR_ERR(trans) != -ENOENT) {
-               return PTR_ERR(trans);
-       }
-
        /* the disk copy procedure reuses the scrub code */
        mutex_lock(&fs_info->volume_mutex);
        ret = btrfs_find_device_by_user_input(root, args->start.srcdevid,
@@ -354,6 +341,19 @@ int btrfs_dev_replace_start(struct btrfs_root *root,
        if (ret)
                return ret;
 
+       /*
+        * Here we commit the transaction to make sure commit_total_bytes
+        * of all the devices are updated.
+        */
+       trans = btrfs_attach_transaction(root);
+       if (!IS_ERR(trans)) {
+               ret = btrfs_commit_transaction(trans, root);
+               if (ret)
+                       return ret;
+       } else if (PTR_ERR(trans) != -ENOENT) {
+               return PTR_ERR(trans);
+       }
+
        btrfs_dev_replace_lock(dev_replace);
        switch (dev_replace->replace_state) {
        case BTRFS_IOCTL_DEV_REPLACE_STATE_NEVER_STARTED:
-- 
2.4.1

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