• Mike Snitzer's avatar
    dm: retain table limits when swapping to new table with no devices · 3ae70656
    Mike Snitzer authored
    Add a safety net that will re-use the DM device's existing limits in the
    event that DM device has a temporary table that doesn't have any
    component devices.  This is to reduce the chance that requests not
    respecting the hardware limits will reach the device.
    
    DM recalculates queue limits based only on devices which currently exist
    in the table.  This creates a problem in the event all devices are
    temporarily removed such as all paths being lost in multipath.  DM will
    reset the limits to the maximum permissible, which can then assemble
    requests which exceed the limits of the paths when the paths are
    restored.  The request will fail the blk_rq_check_limits() test when
    sent to a path with lower limits, and will be retried without end by
    multipath.  This became a much bigger issue after v3.6 commit fe86cdce
    ("block: do not artificially constrain max_sectors for stacking
    drivers").
    Reported-by: default avatarDavid Jeffery <djeffery@redhat.com>
    Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
    Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
    3ae70656
dm.h 4.77 KB