Hi, When one request is dispatched to LLD via dm-rq, if the result is BLK_STS_*RESOURCE, dm-rq will free the request. However, LLD may allocate private stuff for this request, so this way will cause memory leak. Add .cleanup_rq() callback and implement it in SCSI for fixing the issue. And SCSI is the only driver which allocates private stuff in .queue_rq() path. Another use case of this callback is to free the request and re-submit bios during cpu hotplug when the hctx is dead, see the following link: https://lore.kernel.org/linux-block/f122e8f2-5ede-2d83-9ca0-bc713ce66d01@xxxxxxxxxx/T/#t Ming Lei (2): blk-mq: add callback of .cleanup_rq scsi: implement .cleanup_rq callback drivers/md/dm-rq.c | 1 + drivers/scsi/scsi_lib.c | 15 +++++++++++++++ include/linux/blk-mq.h | 13 +++++++++++++ 3 files changed, 29 insertions(+) Cc: Ewan D. Milne <emilne@xxxxxxxxxx> Cc: Bart Van Assche <bvanassche@xxxxxxx> Cc: Hannes Reinecke <hare@xxxxxxxx> Cc: Christoph Hellwig <hch@xxxxxx> Cc: Mike Snitzer <snitzer@xxxxxxxxxx> Cc: dm-devel@xxxxxxxxxx Cc: <stable@xxxxxxxxxxxxxxx> Fixes: 396eaf21ee17 ("blk-mq: improve DM's blk-mq IO merging via blk_insert_cloned_request feedback") -- 2.20.1
