Hello,
In ll_front_merge_fn, the request size result of the eventual front
merge of a BIO with a request is checked against the maximum
size allowed for the request using blk_rq_get_max_sectors. This
function will also check that the merge result will not span block
chunks for chunked block devices using the function blk_max_size_offset.
However, blk_rq_get_max_sectors always calls blk_max_size_offset using
the request sector position, which in the case of a front merge is not
the position at which the merged request would be issued: the sector
position to use must be that of the BIO, and not that of the request.
This problem can trigger a “boundary violation error” for write
requests on ZAC/ZBC host-managed SMR disks as the last write BIO
of a zone (a chunk) can end up being front-merged with the first
request of the following zone (chunk).
The attached patch against linux-4.5-rc2 fixes this problem by adding
an offset argument to the function blk_rq_get_max_sectors.
Best regards.
diff -Naur linux-4.5-rc2/block/blk-merge.c linux-4.5-rc2-patched/block/blk-merge.c
--- linux-4.5-rc2/block/blk-merge.c 2016-02-01 11:12:16.000000000 +0900
+++ linux-4.5-rc2-patched/block/blk-merge.c 2016-02-02 15:28:07.626107509 +0900
@@ -504,7 +504,7 @@
integrity_req_gap_back_merge(req, bio))
return 0;
if (blk_rq_sectors(req) + bio_sectors(bio) >
- blk_rq_get_max_sectors(req)) {
+ blk_rq_get_max_sectors(req, blk_rq_pos(req))) {
req->cmd_flags |= REQ_NOMERGE;
if (req == q->last_merge)
q->last_merge = NULL;
@@ -528,7 +528,7 @@
integrity_req_gap_front_merge(req, bio))
return 0;
if (blk_rq_sectors(req) + bio_sectors(bio) >
- blk_rq_get_max_sectors(req)) {
+ blk_rq_get_max_sectors(req, bio->bi_iter.bi_sector)) {
req->cmd_flags |= REQ_NOMERGE;
if (req == q->last_merge)
q->last_merge = NULL;
@@ -574,7 +574,7 @@
* Will it become too large?
*/
if ((blk_rq_sectors(req) + blk_rq_sectors(next)) >
- blk_rq_get_max_sectors(req))
+ blk_rq_get_max_sectors(req, blk_rq_pos(req)))
return 0;
total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
diff -Naur linux-4.5-rc2/include/linux/blkdev.h linux-4.5-rc2-patched/include/linux/blkdev.h
--- linux-4.5-rc2/include/linux/blkdev.h 2016-02-01 11:12:16.000000000 +0900
+++ linux-4.5-rc2-patched/include/linux/blkdev.h 2016-02-02 15:26:39.313283902 +0900
@@ -888,7 +888,8 @@
(offset & (q->limits.chunk_sectors - 1));
}
-static inline unsigned int blk_rq_get_max_sectors(struct request *rq)
+static inline unsigned int blk_rq_get_max_sectors(struct request *rq,
+ sector_t offset)
{
struct request_queue *q = rq->q;
@@ -898,7 +899,7 @@
if (!q->limits.chunk_sectors || (rq->cmd_flags & REQ_DISCARD))
return blk_queue_get_max_sectors(q, rq->cmd_flags);
- return min(blk_max_size_offset(q, blk_rq_pos(rq)),
+ return min(blk_max_size_offset(q, offset),
blk_queue_get_max_sectors(q, rq->cmd_flags));
}
--
Damien Le Moal,
System Software Group, WW Research,
HGST, a Western Digital company
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Attachment:
bio-merge-size-check.patch
Description: bio-merge-size-check.patch
