Thread (8 messages) 8 messages, 4 authors, 2023-02-17

Re: [PATCH] blk-mq: enforce op-specific segment limits in blk_insert_cloned_request

From: Christoph Hellwig <hch@infradead.org>
Date: 2023-02-17 16:17:05
Also in: dm-devel

On Thu, Feb 16, 2023 at 12:27:02PM -0700, Uday Shankar wrote:
 * 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?
The concern is still valid, but it does not refer to the debug check.
It refers to recalculating nr_phys_segments using
blk_recalc_rq_segments, and the fact that any driver using this
interface needs to stack its limits properly.
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