• Mikulas Patocka's avatar
    dm snapshot: suspend merging snapshot when doing exception handover · 09ee96b2
    Mikulas Patocka authored
    The "dm snapshot: suspend origin when doing exception handover" commit
    fixed a exception store handover bug associated with pending exceptions
    to the "snapshot-origin" target.
    
    However, a similar problem exists in snapshot merging.  When snapshot
    merging is in progress, we use the target "snapshot-merge" instead of
    "snapshot-origin".  Consequently, during exception store handover, we
    must find the snapshot-merge target and suspend its associated
    mapped_device.
    
    To avoid lockdep warnings, the target must be suspended and resumed
    without holding _origins_lock.
    
    Introduce a dm_hold() function that grabs a reference on a
    mapped_device, but unlike dm_get(), it doesn't crash if the device has
    the DMF_FREEING flag set, it returns an error in this case.
    
    In snapshot_resume() we grab the reference to the origin device using
    dm_hold() while holding _origins_lock (_origins_lock guarantees that the
    device won't disappear).  Then we release _origins_lock, suspend the
    device and grab _origins_lock again.
    
    NOTE to stable@ people:
    When backporting to kernels 3.18 and older, use dm_internal_suspend and
    dm_internal_resume instead of dm_internal_suspend_fast and
    dm_internal_resume_fast.
    Signed-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
    Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
    Cc: stable@vger.kernel.org
    09ee96b2
dm.c 76.5 KB