• Jan Kara's avatar
    ext4: Fix Direct I/O locking · 7fb5409d
    Jan Kara authored
    
    
    We cannot start transaction in ext4_direct_IO() and just let it last
    during the whole write because dio_get_page() acquires mmap_sem which
    ranks above transaction start (e.g. because we have dependency chain
    mmap_sem->PageLock->journal_start, or because we update atime while
    holding mmap_sem) and thus deadlocks could happen. We solve the problem
    by starting a transaction separately for each ext4_get_block() call.
    
    We *could* have a problem that we allocate a block and before its data
    are written out the machine crashes and thus we expose stale data. But
    that does not happen because for hole-filling generic code falls back to
    buffered writes and for file extension, we add inode to orphan list and
    thus in case of crash, journal replay will truncate inode back to the
    original size.
    
    Signed-off-by: default avatarJan Kara <jack@suse.cz>
    Signed-off-by: default avatarMingming Cao <cmm@us.ibm.com>
    Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
    7fb5409d