[dm-devel] blk-mq: enforce op-specific segment limits in blk_insert_cloned_request

[Mike Snitzer]

On Thu, Feb 16 2023 at  2:27P -0500,
Uday Shankar <ushankar at purestorage.com> wrote:

> On Wed, Feb 15, 2023 at 10:09:36PM -0800, Christoph Hellwig wrote:
> > I'd just remove the debug check entirely
> 
> Older kernels have these checks in a separate function called
> blk_cloned_rq_check_limits, which carries the following comment:
> 
> /**
>  * blk_cloned_rq_check_limits - Helper function to check a cloned request
>  *                              for the new queue limits
>  * @q:  the queue
>  * @rq: the request being checked
>  *
>  * Description:
>  *    @rq may have been made based on weaker limitations of upper-level queues
>  *    in request stacking drivers, and it may violate the limitation of @q.
>  *    Since the block layer and the underlying device driver trust @rq
>  *    after it is inserted to @q, it should be checked against @q before
>  *    the insertion using this generic function.
>  *
>  *    Request stacking drivers like request-based dm may change the queue
>  *    limits when retrying requests on other queues. Those requests need
>  *    to be checked against the new queue limits again during dispatch.
>  */.
> 
> Is this concern no longer relevant?

Still relevant.