• Lukas Czerner's avatar
    fs: Fix page cache inconsistency when mixing buffered and AIO DIO · 332391a9
    Lukas Czerner authored
    Currently when mixing buffered reads and asynchronous direct writes it
    is possible to end up with the situation where we have stale data in the
    page cache while the new data is already written to disk. This is
    permanent until the affected pages are flushed away. Despite the fact
    that mixing buffered and direct IO is ill-advised it does pose a thread
    for a data integrity, is unexpected and should be fixed.
    
    Fix this by deferring completion of asynchronous direct writes to a
    process context in the case that there are mapped pages to be found in
    the inode. Later before the completion in dio_complete() invalidate
    the pages in question. This ensures that after the completion the pages
    in the written area are either unmapped, or populated with up-to-date
    data. Also do the same for the iomap case which uses
    iomap_dio_complete() instead.
    
    This has a side effect of deferring the completion to a process context
    for every AIO DIO that happens on inode that has pages mapped. However
    since the consensus is that this is ill-advised practice the performance
    implication should not be a problem.
    
    This was based on proposal from Jeff Moyer, thanks!
    Reviewed-by: default avatarJan Kara <jack@suse.cz>
    Reviewed-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
    Reviewed-by: default avatarJeff Moyer <jmoyer@redhat.com>
    Signed-off-by: default avatarLukas Czerner <lczerner@redhat.com>
    Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
    332391a9
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