ext4: Fix double-free of blocks with EXT4_IOC_MOVE_EXT
At the beginning of ext4_move_extent(), we call ext4_discard_preallocations() to discard inode PAs of orig and donor inodes. But in the following case, blocks can be double freed, so move ext4_discard_preallocations() to the end of ext4_move_extents(). 1. Discard inode PAs of orig and donor inodes with ext4_discard_preallocations() in ext4_move_extents(). orig : [ DATA1 ] donor: [ DATA2 ] 2. While data blocks are exchanging between orig and donor inodes, new inode PAs is created to orig by other process's block allocation. (Since there are semaphore gaps in ext4_move_extents().) And new inode PAs is used partially (2-1). 2-1 Create new inode PAs to orig inode orig : [ DATA1 | used PA1 | free PA1 ] donor: [ DATA2 ] 3. Donor inode which has old orig inode's blocks is deleted after EXT4_IOC_MOVE_EXT finished (3-1, 3-2). So the block bitmap corresponds to old orig inode's blocks are freed. 3-1 After EXT4_IOC_MOVE_EXT finished orig : [ DATA2 | free PA1 ] donor: [ DATA1 | used PA1 ] 3-2 Delete donor inode orig : [ DATA2 | free PA1 ] donor: [ FREE SPACE(DATA1) | FREE SPACE(used PA1) ] 4. The double-free of blocks is occurred, when close() is called to orig inode. Because ext4_discard_preallocations() for orig inode frees used PA1 and free PA1, though used PA1 is already freed in 3. 4-1 Double-free of blocks is occurred orig : [ DATA2 | FREE SPACE(free PA1) ] donor: [ FREE SPACE(DATA1) | DOUBLE FREE(used PA1) ] Signed-off-by:Akira Fujita <a-fujita@rs.jp.nec.com> Signed-off-by: