• Alain Renaud's avatar
    xfs: xfs_vm_writepage clear iomap_valid when !buffer_uptodate (REV2) · 66f93113
    Alain Renaud authored
    On filesytems with a block size smaller than PAGE_SIZE we currently have
    a problem with unwritten extents.  If a we have multi-block page for
    which an unwritten extent has been allocated, and only some of the
    buffers have been written to, and they are not contiguous, we can expose
    stale data from disk in the blocks between the writes after extent
    conversion.
    
    Example of a page with unwritten and real data.
    buffer  content
    0       empty  b_state = 0
    1       DATA   b_state = 0x1023 Uptodate,Dirty,Mapped,Unwritten
    2       DATA   b_state = 0x1023 Uptodate,Dirty,Mapped,Unwritten
    3       empty  b_state = 0
    4       empty  b_state = 0
    5       DATA   b_state = 0x1023 Uptodate,Dirty,Mapped,Unwritten
    6       DATA   b_state = 0x1023 Uptodate,Dirty,Mapped,Unwritten
    7       empty  b_state = 0
    
    Buffers 1, 2, 5, and 6 have been written to, leaving 0, 3, 4, and 7
    empty.  Currently buffers 1, 2, 5, and 6 are added to a single ioend,
    and when IO has completed, extent conversion creates a real extent from
    block 1 through block 6, leaving 0 and 7 unwritten.  However buffers 3
    and 4 were not written to disk, so stale data is exposed from those
    blocks on a subsequent read.
    
    Fix this by setting iomap_valid = 0 when we find a buffer that is not
    Uptodate.  This ensures that buffers 5 and 6 are not added to the same
    ioend as buffers 1 and 2.  Later these blocks will be converted into two
    separate real extents, leaving the blocks in between unwritten.
    Signed-off-by: default avatarAlain Renaud <arenaud@sgi.com>
    Reviewed-by: default avatarDave Chinner <dchinner@redhat.com>
    Signed-off-by: default avatarBen Myers <bpm@sgi.com>
    66f93113
xfs_aops.c 39.5 KB