scsi_dh: fix use-after-free when removing scsi device

scsi_dh: fix use-after-free when removing scsi device

The commit 1bab0de0274f ("dm-mpath, scsi_dh: don't let dm detach device
handlers") removed reference counting of attached scsi device handler.
As a result, handler data is freed immediately via scsi_dh->detach()
in the context of scsi_remove_device() where activation request can be
still in flight.

This patch moves scsi_dh_handler_detach() to sdev releasing function,
scsi_device_dev_release_usercontext(), at that point the device
is already in quiesced state.

Fixes: 1bab0de0274f ("dm-mpath, scsi_dh: don't let dm detach device handlers")
Signed-off-by: Jun'ichi Nomura <[email protected]>
Acked-by: Christoph Hellwig <[email protected]>
Signed-off-by: James Bottomley <[email protected]>