• Ming Lei's avatar
    blk-mq: add callback of .cleanup_rq · 226b4fc7
    Ming Lei authored
    SCSI maintains its own driver private data hooked off of each SCSI
    request, and the pridate data won't be freed after scsi_queue_rq()
    returns BLK_STS_RESOURCE or BLK_STS_DEV_RESOURCE. An upper layer driver
    (e.g. dm-rq) may need to retry these SCSI requests, before SCSI has
    fully dispatched them, due to a lower level SCSI driver's resource
    limitation identified in scsi_queue_rq(). Currently SCSI's per-request
    private data is leaked when the upper layer driver (dm-rq) frees and
    then retries these requests in response to BLK_STS_RESOURCE or
    BLK_STS_DEV_RESOURCE returns from scsi_queue_rq().
    
    This usecase is so specialized that it doesn't warrant training an
    existing blk-mq interface (e.g. blk_mq_free_request) to allow SCSI to
    account for freeing its driver private data -- doing so would add an
    extra branch for handling a special case that all other consumers of
    SCSI (and blk-mq) won't ever need to worry about.
    
    So the most pragmatic way forward is to delegate freeing SCSI driver
    private data to the upper layer driver (dm-rq).  Do so by adding
    new .cleanup_rq callback and calling a new blk_mq_cleanup_rq() method
    from dm-rq.  A following commit will implement the .cleanup_rq() hook
    in scsi_mq_ops.
    
    Cc: Ewan D. Milne <emilne@redhat.com>
    Cc: Bart Van Assche <bvanassche@acm.org>
    Cc: Hannes Reinecke <hare@suse.com>
    Cc: Christoph Hellwig <hch@lst.de>
    Cc: Mike Snitzer <snitzer@redhat.com>
    Cc: dm-devel@redhat.com
    Cc: <stable@vger.kernel.org>
    Fixes: 396eaf21 ("blk-mq: improve DM's blk-mq IO merging via blk_insert_cloned_request feedback")
    Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
    Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
    226b4fc7
dm-rq.c 15.3 KB