[PATCH] block: recompute nr_integrity_segments in blk_insert_cloned_request

[Casey Chen <cachen@purestorage.com>]

blk_insert_cloned_request() already recomputes nr_phys_segments
against the bottom queue, because "the queue settings related to
segment counting may differ from the original queue." The exact same
reasoning applies to integrity segments: a stacked driver's underlying
queue can have tighter virt_boundary_mask, seg_boundary_mask, or
max_segment_size than the top queue, in which case
blk_rq_count_integrity_sg() against the bottom queue produces a
different count than the cached rq->nr_integrity_segments inherited
from the source request by blk_rq_prep_clone().

When the cached count is lower than the bottom queue's actual count,
blk_rq_map_integrity_sg() trips

	BUG_ON(segments > rq->nr_integrity_segments);

on dispatch. The same families of stacked setups that motivated the
existing nr_phys_segments recompute -- dm-multipath fanning out to
nvme-rdma in particular -- can produce this.

Mirror the nr_phys_segments handling: when the request carries
integrity, recompute nr_integrity_segments against the bottom queue
and reject the request if it exceeds the bottom queue's
max_integrity_segments. blk_rq_count_integrity_sg() and
queue_max_integrity_segments() are both already available via
<linux/blk-integrity.h>, which blk-mq.c includes.

This closes a latent gap in the stacking contract and brings the
integrity-segment accounting in line with the existing
phys-segment accounting.

Fixes: 76c313f658d2 ("blk-integrity: improved sg segment mapping")
Signed-off-by: Casey Chen <cachen@purestorage.com>
---
 block/blk-mq.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 4c5c16cce4f8..d0c37daf568f 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -3307,6 +3307,25 @@ blk_status_t blk_insert_cloned_request(struct request *rq)
 		return BLK_STS_IOERR;
 	}
 
+	/*
+	 * Integrity segment counting depends on the same queue limits
+	 * (virt_boundary_mask, seg_boundary_mask, max_segment_size) that
+	 * vary across stacked queues, so recompute against the bottom
+	 * queue just like nr_phys_segments above.
+	 */
+	if (blk_integrity_rq(rq) && rq->bio) {
+		unsigned short max_int_segs = queue_max_integrity_segments(q);
+
+		rq->nr_integrity_segments =
+			blk_rq_count_integrity_sg(rq->q, rq->bio);
+		if (rq->nr_integrity_segments > max_int_segs) {
+			printk(KERN_ERR "%s: over max integrity segments limit. (%u > %u)\n",
+				__func__, rq->nr_integrity_segments,
+				max_int_segs);
+			return BLK_STS_IOERR;
+		}
+	}
+
 	if (q->disk && should_fail_request(q->disk->part0, blk_rq_bytes(rq)))
 		return BLK_STS_IOERR;
 
-- 
2.50.1