[PATCH V3 0/2] block/scsi/dm-rq: fix leak of request private data in dm-mpath

[Ming Lei <ming.lei@redhat.com>]

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 data for this request, so this way will cause memory leak.

Add .cleanup_rq() callback and implement it in SCSI for fixing the issue,
since SCSI is the only driver which allocates private requst data 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@huawei.com/T/#t

V3:
	- run .cleanup_rq() from dm-rq because this issue is dm-rq specific,
	and even in future it should be still very unusual to free request
	in this way. If we call .cleanup_rq() in generic rq free code(fast
	path), cost will be introduced unnecessarily, also we have to
	consider related race.

V2:
	- run .cleanup_rq() in blk_mq_free_request(), as suggested by Mike 


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 | 13 +++++++++++++
 include/linux/blk-mq.h  | 13 +++++++++++++
 3 files changed, 27 insertions(+)

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: 396eaf21ee17 ("blk-mq: improve DM's blk-mq IO merging via blk_insert_cloned_request feedback")
-- 
2.20.1