On Fri, 2017-05-26 at 08:34 +0200, Christoph Hellwig wrote:
> On Thu, May 25, 2017 at 11:43:16AM -0700, Bart Van Assche wrote:
> > Several block drivers need to initialize the driver-private data
> > after having called blk_get_request() and before .prep_rq_fn() is
> > called, e.g. when submitting a REQ_OP_SCSI_* request. Avoid that
> > that initialization code has to be repeated after every
> > blk_get_request() call by adding a new callback function to struct
> > request_queue.
>
> I still think we should do this at the end of blk_mq_alloc_request /
> blk_old_get_request to exactly keep the old semantics and keep the
> calls out of the hot path.
Hello Christoph,
I have tried to move that call into blk_mq_alloc_request() but that
resulted in a kernel oops during boot due to scsi_add_cmd_to_list()
dereferencing scsi_cmnd.device and due to that pointer being invalid.
I think that pointer was invalid because moving the initialize_rq_fn()
call into blk_mq_alloc_request() caused request initialization to be
skipped for the following code path:
submit_bio()
-> generic_make_request()
-> .make_request_fn == blk_mq_make_request()
-> blk_mq_sched_get_request()
-> __blk_mq_alloc_request()
-> blk_mq_rq_ctx_init()
This is why I would like to keep the .initialize_rq_fn() call in
blk_mq_rq_ctx_init().
Bart.
