[PATCH 0/4] bugfix of logical_block_size and make it configurable

[PATCH 0/4] bugfix of logical_block_size and make it configurable

[linan666]

From: Li Nan <linan122@huawei.com>

Li Nan (4):
  block: factor out a helper to set logical/physical block size
  md: make raid logical_block_size configurable
  md: prevent adding disks with larger logical_block_size to active
    arrays
  md: Fix the return value of mddev_stack_new_rdev

 drivers/md/md.h                |  1 +
 include/linux/blkdev.h         |  2 +
 include/uapi/linux/raid/md_p.h |  6 ++-
 block/blk-settings.c           | 85 +++++++++++++++++++---------------
 drivers/md/md-linear.c         |  1 +
 drivers/md/md.c                | 83 ++++++++++++++++++++++++++++++++-
 drivers/md/raid0.c             |  1 +
 drivers/md/raid1.c             |  1 +
 drivers/md/raid10.c            |  1 +
 drivers/md/raid5.c             |  1 +
 10 files changed, 142 insertions(+), 40 deletions(-)

-- 
2.39.2

[PATCH 1/4] block: factor out a helper to set logical/physical block size

[linan666]

From: Li Nan <linan122@huawei.com>

There is no functional change.

Signed-off-by: Li Nan <linan122@huawei.com>
---
 include/linux/blkdev.h |  2 +
 block/blk-settings.c   | 85 ++++++++++++++++++++++++------------------
 2 files changed, 50 insertions(+), 37 deletions(-)

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 248416ecd01c..516a7a8c0c3d 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -996,6 +996,8 @@ static inline void blk_queue_disable_write_zeroes(struct request_queue *q)
  */
 extern void blk_set_queue_depth(struct request_queue *q, unsigned int depth);
 extern void blk_set_stacking_limits(struct queue_limits *lim);
+extern int blk_set_block_size(struct queue_limits *t, unsigned int logical_block_size,
+		unsigned int physical_block_size);
 extern int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
 			    sector_t offset);
 void queue_limits_stack_bdev(struct queue_limits *t, struct block_device *bdev,
diff --git a/block/blk-settings.c b/block/blk-settings.c
index c44dadc35e1e..4a053c3d7c0a 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -645,6 +645,53 @@ static void blk_stack_atomic_writes_limits(struct queue_limits *t,
 	t->atomic_write_hw_boundary = 0;
 }
 
+int blk_set_block_size(struct queue_limits *t, unsigned int logical_block_size,
+		     unsigned int physical_block_size)
+{
+	int ret = 0;
+
+	t->logical_block_size = max(t->logical_block_size,
+				    logical_block_size);
+
+	t->physical_block_size = max(t->physical_block_size,
+				     physical_block_size);
+
+	/* Physical block size a multiple of the logical block size? */
+	if (t->physical_block_size & (t->logical_block_size - 1)) {
+		t->physical_block_size = t->logical_block_size;
+		t->flags |= BLK_FLAG_MISALIGNED;
+		ret = -1;
+	}
+
+	/* Minimum I/O a multiple of the physical block size? */
+	if (t->io_min & (t->physical_block_size - 1)) {
+		t->io_min = t->physical_block_size;
+		t->flags |= BLK_FLAG_MISALIGNED;
+		ret = -1;
+	}
+
+	/* Optimal I/O a multiple of the physical block size? */
+	if (t->io_opt & (t->physical_block_size - 1)) {
+		t->io_opt = 0;
+		t->flags |= BLK_FLAG_MISALIGNED;
+		ret = -1;
+	}
+
+	/* chunk_sectors a multiple of the physical block size? */
+	if ((t->chunk_sectors << 9) & (t->physical_block_size - 1)) {
+		t->chunk_sectors = 0;
+		t->flags |= BLK_FLAG_MISALIGNED;
+		ret = -1;
+	}
+
+	t->max_sectors = blk_round_down_sectors(t->max_sectors, t->logical_block_size);
+	t->max_hw_sectors = blk_round_down_sectors(t->max_hw_sectors, t->logical_block_size);
+	t->max_dev_sectors = blk_round_down_sectors(t->max_dev_sectors, t->logical_block_size);
+
+	return ret;
+}
+EXPORT_SYMBOL(blk_set_block_size);
+
 /**
  * blk_stack_limits - adjust queue_limits for stacked devices
  * @t:	the stacking driver limits (top device)
@@ -728,12 +775,6 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
 		}
 	}
 
-	t->logical_block_size = max(t->logical_block_size,
-				    b->logical_block_size);
-
-	t->physical_block_size = max(t->physical_block_size,
-				     b->physical_block_size);
-
 	t->io_min = max(t->io_min, b->io_min);
 	t->io_opt = lcm_not_zero(t->io_opt, b->io_opt);
 	t->dma_alignment = max(t->dma_alignment, b->dma_alignment);
@@ -742,33 +783,7 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
 	if (b->chunk_sectors)
 		t->chunk_sectors = gcd(t->chunk_sectors, b->chunk_sectors);
 
-	/* Physical block size a multiple of the logical block size? */
-	if (t->physical_block_size & (t->logical_block_size - 1)) {
-		t->physical_block_size = t->logical_block_size;
-		t->flags |= BLK_FLAG_MISALIGNED;
-		ret = -1;
-	}
-
-	/* Minimum I/O a multiple of the physical block size? */
-	if (t->io_min & (t->physical_block_size - 1)) {
-		t->io_min = t->physical_block_size;
-		t->flags |= BLK_FLAG_MISALIGNED;
-		ret = -1;
-	}
-
-	/* Optimal I/O a multiple of the physical block size? */
-	if (t->io_opt & (t->physical_block_size - 1)) {
-		t->io_opt = 0;
-		t->flags |= BLK_FLAG_MISALIGNED;
-		ret = -1;
-	}
-
-	/* chunk_sectors a multiple of the physical block size? */
-	if ((t->chunk_sectors << 9) & (t->physical_block_size - 1)) {
-		t->chunk_sectors = 0;
-		t->flags |= BLK_FLAG_MISALIGNED;
-		ret = -1;
-	}
+	ret = blk_set_block_size(t, b->logical_block_size, b->physical_block_size);
 
 	/* Find lowest common alignment_offset */
 	t->alignment_offset = lcm_not_zero(t->alignment_offset, alignment)
@@ -780,10 +795,6 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
 		ret = -1;
 	}
 
-	t->max_sectors = blk_round_down_sectors(t->max_sectors, t->logical_block_size);
-	t->max_hw_sectors = blk_round_down_sectors(t->max_hw_sectors, t->logical_block_size);
-	t->max_dev_sectors = blk_round_down_sectors(t->max_dev_sectors, t->logical_block_size);
-
 	/* Discard alignment and granularity */
 	if (b->discard_granularity) {
 		alignment = queue_limit_discard_alignment(b, start);
-- 
2.39.2

[PATCH 2/4] md: make raid logical_block_size configurable

[linan666]

From: Li Nan <linan122@huawei.com>

Previously, raid array used the maximum logical_block_size (LBS) from
all member disks. Adding disks with larger LBS during operation could
unexpectedly increase RAID's LBS, risking existing partition data loss.
Simply restricting larger-LBS disks is inflexible. In some scenarios,
only disks with 512 LBS are available currently, but later, disks with
4k LBS may be added to the array.

Making LBS configurable is the best way to solve this scenario.
After this patch, the raid will:
  - handle LBS fields in disk metadata read/write operations.
  - introduce a new sysfs 'md/logical_block_size' for LBS configuration.

Future mdadm should support setting LBS via metadata field during RAID
creation and the new sysfs. Though the kernel allows runtime LBS changes,
users should avoid modifying it after creating partitions or filesystems
to prevent compatibility issues.

Signed-off-by: Li Nan <linan122@huawei.com>
---
 drivers/md/md.h                |  1 +
 include/uapi/linux/raid/md_p.h |  6 ++-
 drivers/md/md-linear.c         |  1 +
 drivers/md/md.c                | 74 ++++++++++++++++++++++++++++++++++
 drivers/md/raid0.c             |  1 +
 drivers/md/raid1.c             |  1 +
 drivers/md/raid10.c            |  1 +
 drivers/md/raid5.c             |  1 +
 8 files changed, 84 insertions(+), 2 deletions(-)

diff --git a/drivers/md/md.h b/drivers/md/md.h
index def808064ad8..96bd10998ae0 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -403,6 +403,7 @@ struct mddev {
 	sector_t			array_sectors; /* exported array size */
 	int				external_size; /* size managed
 							* externally */
+	unsigned int			logical_block_size;
 	__u64				events;
 	/* If the last 'event' was simply a clean->dirty transition, and
 	 * we didn't write it to the spares, then it is safe and simple
diff --git a/include/uapi/linux/raid/md_p.h b/include/uapi/linux/raid/md_p.h
index ff47b6f0ba0f..ad1c84e772ba 100644
--- a/include/uapi/linux/raid/md_p.h
+++ b/include/uapi/linux/raid/md_p.h
@@ -180,7 +180,8 @@ typedef struct mdp_superblock_s {
 	__u32 delta_disks;	/* 15 change in number of raid_disks	      */
 	__u32 new_layout;	/* 16 new layout			      */
 	__u32 new_chunk;	/* 17 new chunk size (bytes)		      */
-	__u32 gstate_sreserved[MD_SB_GENERIC_STATE_WORDS - 18];
+	__u32 logical_block_size;	/* same as q->limits->logical_block_size */
+	__u32 gstate_sreserved[MD_SB_GENERIC_STATE_WORDS - 19];
 
 	/*
 	 * Personality information
@@ -291,7 +292,8 @@ struct mdp_superblock_1 {
 	__le64	resync_offset;	/* data before this offset (from data_offset) known to be in sync */
 	__le32	sb_csum;	/* checksum up to devs[max_dev] */
 	__le32	max_dev;	/* size of devs[] array to consider */
-	__u8	pad3[64-32];	/* set to 0 when writing */
+	__le32  logical_block_size;	/* same as q->limits->logical_block_size */
+	__u8	pad3[64-36];	/* set to 0 when writing */
 
 	/* device state information. Indexed by dev_number.
 	 * 2 bytes per device
diff --git a/drivers/md/md-linear.c b/drivers/md/md-linear.c
index 369aed044b40..c197a90a6bd5 100644
--- a/drivers/md/md-linear.c
+++ b/drivers/md/md-linear.c
@@ -73,6 +73,7 @@ static int linear_set_limits(struct mddev *mddev)
 
 	md_init_stacking_limits(&lim);
 	lim.max_hw_sectors = mddev->chunk_sectors;
+	lim.logical_block_size = mddev->logical_block_size;
 	lim.max_write_zeroes_sectors = mddev->chunk_sectors;
 	lim.io_min = mddev->chunk_sectors << 9;
 	err = mddev_stack_rdev_limits(mddev, &lim, MDDEV_STACK_INTEGRITY);
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 827646b3eb59..cf3d8ff807a7 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1335,6 +1335,7 @@ static int super_90_validate(struct mddev *mddev, struct md_rdev *freshest, stru
 		mddev->bitmap_info.default_offset = MD_SB_BYTES >> 9;
 		mddev->bitmap_info.default_space = 64*2 - (MD_SB_BYTES >> 9);
 		mddev->reshape_backwards = 0;
+		mddev->logical_block_size = sb->logical_block_size;
 
 		if (mddev->minor_version >= 91) {
 			mddev->reshape_position = sb->reshape_position;
@@ -1497,6 +1498,7 @@ static void super_90_sync(struct mddev *mddev, struct md_rdev *rdev)
 
 	sb->layout = mddev->layout;
 	sb->chunk_size = mddev->chunk_sectors << 9;
+	sb->logical_block_size = mddev->logical_block_size;
 
 	if (mddev->bitmap && mddev->bitmap_info.file == NULL)
 		sb->state |= (1<<MD_SB_BITMAP_PRESENT);
@@ -1831,6 +1833,7 @@ static int super_1_validate(struct mddev *mddev, struct md_rdev *freshest, struc
 		mddev->layout = le32_to_cpu(sb->layout);
 		mddev->raid_disks = le32_to_cpu(sb->raid_disks);
 		mddev->dev_sectors = le64_to_cpu(sb->size);
+		mddev->logical_block_size = le32_to_cpu(sb->logical_block_size);
 		mddev->events = ev1;
 		mddev->bitmap_info.offset = 0;
 		mddev->bitmap_info.space = 0;
@@ -2040,6 +2043,7 @@ static void super_1_sync(struct mddev *mddev, struct md_rdev *rdev)
 	sb->chunksize = cpu_to_le32(mddev->chunk_sectors);
 	sb->level = cpu_to_le32(mddev->level);
 	sb->layout = cpu_to_le32(mddev->layout);
+	sb->logical_block_size = cpu_to_le32(mddev->logical_block_size);
 	if (test_bit(FailFast, &rdev->flags))
 		sb->devflags |= FailFast1;
 	else
@@ -5630,6 +5634,65 @@ static struct md_sysfs_entry md_serialize_policy =
 __ATTR(serialize_policy, S_IRUGO | S_IWUSR, serialize_policy_show,
        serialize_policy_store);
 
+static int mddev_set_logical_block_size(struct mddev *mddev,
+				unsigned int lbs)
+{
+	int err = 0;
+	struct queue_limits lim;
+
+	if (blk_validate_block_size(lbs) ||
+	    queue_logical_block_size(mddev->gendisk->queue) >= lbs) {
+		pr_err("%s: incompatible logical_block_size, can not set\n",
+		       mdname(mddev));
+		return -EINVAL;
+	}
+
+	lim = queue_limits_start_update(mddev->gendisk->queue);
+	if (blk_set_block_size(&lim, lbs, 0))
+		pr_warn("%s: logical_block_size changes, data may be lost\n",
+		       mdname(mddev));
+	err = queue_limits_commit_update(mddev->gendisk->queue, &lim);
+	if (err)
+		return err;
+
+	mddev->logical_block_size = lbs;
+	md_update_sb(mddev, 1);
+
+	return 0;
+}
+
+static ssize_t
+lbs_show(struct mddev *mddev, char *page)
+{
+	return sprintf(page, "%u\n", mddev->logical_block_size);
+}
+
+static ssize_t
+lbs_store(struct mddev *mddev, const char *buf, size_t len)
+{
+	unsigned int lbs;
+	int err;
+
+	err = kstrtouint(buf, 10, &lbs);
+	if (err < 0)
+		return err;
+
+	err = mddev_lock(mddev);
+	if (err)
+		return err;
+	err = -EBUSY;
+	if (mddev->pers)
+		goto unlock;
+
+	err = mddev_set_logical_block_size(mddev, lbs);
+
+unlock:
+	mddev_unlock(mddev);
+	return err ?: len;
+}
+
+static struct md_sysfs_entry md_logical_block_size =
+__ATTR(logical_block_size, S_IRUGO|S_IWUSR, lbs_show, lbs_store);
 
 static struct attribute *md_default_attrs[] = {
 	&md_level.attr,
@@ -5662,6 +5725,7 @@ static struct attribute *md_redundancy_attrs[] = {
 	&md_scan_mode.attr,
 	&md_last_scan_mode.attr,
 	&md_mismatches.attr,
+	&md_logical_block_size.attr,
 	&md_sync_min.attr,
 	&md_sync_max.attr,
 	&md_sync_speed.attr,
@@ -5760,6 +5824,7 @@ int mddev_stack_rdev_limits(struct mddev *mddev, struct queue_limits *lim,
 		unsigned int flags)
 {
 	struct md_rdev *rdev;
+	unsigned int lbs = mddev->logical_block_size;
 
 	rdev_for_each(rdev, mddev) {
 		queue_limits_stack_bdev(lim, rdev->bdev, rdev->data_offset,
@@ -5768,6 +5833,14 @@ int mddev_stack_rdev_limits(struct mddev *mddev, struct queue_limits *lim,
 		    !queue_limits_stack_integrity_bdev(lim, rdev->bdev))
 			return -EINVAL;
 	}
+	if (lbs) {
+		if (lbs != queue_logical_block_size(mddev->gendisk->queue))
+			pr_warn("%s: logical_block_size is changed, before: %u, now: %u\n",
+			mdname(mddev), lbs,
+			queue_logical_block_size(mddev->gendisk->queue));
+	} else {
+		mddev->logical_block_size = queue_logical_block_size(mddev->gendisk->queue);
+	}
 
 	return 0;
 }
@@ -6377,6 +6450,7 @@ static void md_clean(struct mddev *mddev)
 	mddev->chunk_sectors = 0;
 	mddev->ctime = mddev->utime = 0;
 	mddev->layout = 0;
+	mddev->logical_block_size = 0;
 	mddev->max_disks = 0;
 	mddev->events = 0;
 	mddev->can_decrease_events = 0;
diff --git a/drivers/md/raid0.c b/drivers/md/raid0.c
index 70bcc3cdf2cd..83e330e30fc2 100644
--- a/drivers/md/raid0.c
+++ b/drivers/md/raid0.c
@@ -382,6 +382,7 @@ static int raid0_set_limits(struct mddev *mddev)
 	md_init_stacking_limits(&lim);
 	lim.max_hw_sectors = mddev->chunk_sectors;
 	lim.max_write_zeroes_sectors = mddev->chunk_sectors;
+	lim.logical_block_size = mddev->logical_block_size;
 	lim.io_min = mddev->chunk_sectors << 9;
 	lim.io_opt = lim.io_min * mddev->raid_disks;
 	lim.features |= BLK_FEAT_ATOMIC_WRITES;
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 10ea3af40991..5d8a718af9b0 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -3217,6 +3217,7 @@ static int raid1_set_limits(struct mddev *mddev)
 
 	md_init_stacking_limits(&lim);
 	lim.max_write_zeroes_sectors = 0;
+	lim.logical_block_size = mddev->logical_block_size;
 	lim.features |= BLK_FEAT_ATOMIC_WRITES;
 	err = mddev_stack_rdev_limits(mddev, &lim, MDDEV_STACK_INTEGRITY);
 	if (err)
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 15b9ae5bf84d..085188f85785 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -4016,6 +4016,7 @@ static int raid10_set_queue_limits(struct mddev *mddev)
 
 	md_init_stacking_limits(&lim);
 	lim.max_write_zeroes_sectors = 0;
+	lim.logical_block_size = mddev->logical_block_size;
 	lim.io_min = mddev->chunk_sectors << 9;
 	lim.io_opt = lim.io_min * raid10_nr_stripes(conf);
 	lim.features |= BLK_FEAT_ATOMIC_WRITES;
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 5c79429acc64..b11e0ae25c2f 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -7736,6 +7736,7 @@ static int raid5_set_limits(struct mddev *mddev)
 	stripe = roundup_pow_of_two(data_disks * (mddev->chunk_sectors << 9));
 
 	md_init_stacking_limits(&lim);
+	lim.logical_block_size = mddev->logical_block_size;
 	lim.io_min = mddev->chunk_sectors << 9;
 	lim.io_opt = lim.io_min * (conf->raid_disks - conf->max_degraded);
 	lim.features |= BLK_FEAT_RAID_PARTIAL_STRIPES_EXPENSIVE;
-- 
2.39.2

[PATCH 3/4] md: prevent adding disks with larger logical_block_size to active arrays

[linan666]

From: Li Nan <linan122@huawei.com>

When adding a disk to a md array, avoid updating the array's
logical_block_size to match the new disk. This prevents accidental
partition table loss that renders the array unusable.

The later patch will introduce a way to configure the array's
logical_block_size.

Signed-off-by: Li Nan <linan122@huawei.com>
---
 drivers/md/md.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index cf3d8ff807a7..48c35b6fb52e 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -5854,6 +5854,13 @@ int mddev_stack_new_rdev(struct mddev *mddev, struct md_rdev *rdev)
 	if (mddev_is_dm(mddev))
 		return 0;
 
+	if (queue_logical_block_size(rdev->bdev->bd_disk->queue) >
+	    queue_logical_block_size(mddev->gendisk->queue)) {
+		pr_err("%s: incompatible logical_block_size, can not add\n",
+		       mdname(mddev));
+		return -EINVAL;
+	}
+
 	lim = queue_limits_start_update(mddev->gendisk->queue);
 	queue_limits_stack_bdev(&lim, rdev->bdev, rdev->data_offset,
 				mddev->gendisk->disk_name);
-- 
2.39.2

[PATCH 4/4] md: Fix the return value of mddev_stack_new_rdev

[linan666]

From: Li Nan <linan122@huawei.com>

In mddev_stack_new_rdev(), if the integrity profile check fails, it
returns -ENXIO, which means "No such device or address". This is
inaccurate and can mislead users. Change it to return -EINVAL.

Fixes: c6e56cf6b2e7 ("block: move integrity information into queue_limits")
Signed-off-by: Li Nan <linan122@huawei.com>
---
 drivers/md/md.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 48c35b6fb52e..e974280b38bb 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -5869,7 +5869,7 @@ int mddev_stack_new_rdev(struct mddev *mddev, struct md_rdev *rdev)
 		pr_err("%s: incompatible integrity profile for %pg\n",
 		       mdname(mddev), rdev->bdev);
 		queue_limits_cancel_update(mddev->gendisk->queue);
-		return -ENXIO;
+		return -EINVAL;
 	}
 
 	return queue_limits_commit_update(mddev->gendisk->queue, &lim);
-- 
2.39.2

Re: [PATCH 1/4] block: factor out a helper to set logical/physical block size

[Bart Van Assche]

On 3/4/25 4:19 AM, linan666@huaweicloud.com wrote:
> +EXPORT_SYMBOL(blk_set_block_size);

This function is exported without documenting what the requirements are
for calling this function? Yikes.

Is my understanding correct that it is only safe to apply changes made 
with blk_set_block_size() by calling
queue_limits_commit_update_frozen()?

Thanks,

Bart.

Re: [PATCH 1/4] block: factor out a helper to set logical/physical block size

[Li Nan]

Hi, Bart:

Apologies for the delayed response.

在 2025/3/4 22:32, Bart Van Assche 写道:
> On 3/4/25 4:19 AM, linan666@huaweicloud.com wrote:
>> +EXPORT_SYMBOL(blk_set_block_size);
> 
> This function is exported without documenting what the requirements are
> for calling this function? Yikes.
> 

Thank you for your reply, I'll add more
documentation in the next version.


> Is my understanding correct that it is only safe to apply changes made with 
> blk_set_block_size() by calling
> queue_limits_commit_update_frozen()?
> 

Exported func blk_set_block_size() is only used in RAID, with expected
usage similar to queue_limits_stack_bdev(): callers must ensure no pending
IO and use queue_limits_start_update/queue_limits_commit_update to prevent
concurrent modifications.

> Thanks,
> 
> Bart.
> 
> 
> .

-- 
Thanks,
Nan

Re: [PATCH 1/4] block: factor out a helper to set logical/physical block size

[Christoph Hellwig]

On Tue, Mar 04, 2025 at 08:19:15PM +0800, linan666@huaweicloud.com wrote:
> +extern int blk_set_block_size(struct queue_limits *t, unsigned int logical_block_size,

No need for the extern.

> +int blk_set_block_size(struct queue_limits *t, unsigned int logical_block_size,
> +		     unsigned int physical_block_size)


As Bart said this really needs documentation, both in the commit message
and the code.  It appears to be a subset of the queue limits stacking,
but I have no idea why that is needed, and the set_ name also confers
the wrong implications to me gіven the stacking logic.

> +{
> +	int ret = 0;

ret is always 0 or -1, so using a bool would be better.

> +	t->max_sectors = blk_round_down_sectors(t->max_sectors, t->logical_block_size);
> +	t->max_hw_sectors = blk_round_down_sectors(t->max_hw_sectors, t->logical_block_size);
> +	t->max_dev_sectors = blk_round_down_sectors(t->max_dev_sectors, t->logical_block_size);

Please avoid the overly long lines.

> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(blk_set_block_size);

At best this should be a EXPORT_SYMBOL_GPL.