ext4: Fix potential truncate BUG due to i_prealloc_list being non-empty

We need to call ext4_discard_reservation() earlier in ext4_truncate(),
to avoid a BUG() in ext4_mb_return_to_preallocation(), which is called
(ultimately) by ext4_free_blocks().  So we must ditch the blocks on
i_prealloc_list before we start freeing the data blocks.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 3 insertions, 2 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index a1c7d762321..2d54c822c4c 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3494,6 +3494,9 @@ void ext4_truncate(struct inode *inode)
          * modify the block allocation tree.
          */
         down_write(&ei->i_data_sem);
+
+        ext4_discard_reservation(inode);
+
         /*
          * The orphan list entry will now protect us from any crash which
          * occurs before the truncate completes, so it is now safe to propagate
@@ -3563,8 +3566,6 @@ do_indirects:
                 ;
         }
 
-        ext4_discard_reservation(inode);
-
         up_write(&ei->i_data_sem);
         inode->i_mtime = inode->i_ctime = ext4_current_time(inode);
         ext4_mark_inode_dirty(handle, inode);