The patch below does not apply to the 5.9-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
>From 3ee16db390b42b8a21f2ad2ea2518f3469c6e532 Mon Sep 17 00:00:00 2001
From: Mike Snitzer <snitzer@xxxxxxxxxx>
Date: Mon, 30 Nov 2020 10:57:43 -0500
Subject: [PATCH] dm: fix IO splitting
Commit 882ec4e609c1 ("dm table: stack 'chunk_sectors' limit to account
for target-specific splitting") caused a couple regressions:
1) Using lcm_not_zero() when stacking chunk_sectors was a bug because
chunk_sectors must reflect the most limited of all devices in the
IO stack.
2) DM targets that set max_io_len but that do _not_ provide an
.iterate_devices method no longer had there IO split properly.
And commit 5091cdec56fa ("dm: change max_io_len() to use
blk_max_size_offset()") also caused a regression where DM no longer
supported varied (per target) IO splitting. The implication being the
potential for severely reduced performance for IO stacks that use a DM
target like dm-cache to hide performance limitations of a slower
device (e.g. one that requires 4K IO splitting).
Coming full circle: Fix all these issues by discontinuing stacking
chunk_sectors up using ti->max_io_len in dm_calculate_queue_limits(),
add optional chunk_sectors override argument to blk_max_size_offset()
and update DM's max_io_len() to pass ti->max_io_len to its
blk_max_size_offset() call.
Passing in an optional chunk_sectors override to blk_max_size_offset()
allows for code reuse of block's centralized calculation for max IO
size based on provided offset and split boundary.
Fixes: 882ec4e609c1 ("dm table: stack 'chunk_sectors' limit to account for target-specific splitting")
Fixes: 5091cdec56fa ("dm: change max_io_len() to use blk_max_size_offset()")
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: John Dorminy <jdorminy@xxxxxxxxxx>
Reported-by: Bruce Johnston <bjohnsto@xxxxxxxxxx>
Reported-by: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
Reviewed-by: John Dorminy <jdorminy@xxxxxxxxxx>
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Reviewed-by: Jens Axboe <axboe@xxxxxxxxx>
diff --git a/block/blk-merge.c b/block/blk-merge.c
index bcf5e4580603..97b7c2821565 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -144,7 +144,7 @@ static struct bio *blk_bio_write_same_split(struct request_queue *q,
static inline unsigned get_max_io_size(struct request_queue *q,
struct bio *bio)
{
- unsigned sectors = blk_max_size_offset(q, bio->bi_iter.bi_sector);
+ unsigned sectors = blk_max_size_offset(q, bio->bi_iter.bi_sector, 0);
unsigned max_sectors = sectors;
unsigned pbs = queue_physical_block_size(q) >> SECTOR_SHIFT;
unsigned lbs = queue_logical_block_size(q) >> SECTOR_SHIFT;
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 2073ee8d18f4..7eeb7c4169c9 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -18,7 +18,6 @@
#include <linux/mutex.h>
#include <linux/delay.h>
#include <linux/atomic.h>
-#include <linux/lcm.h>
#include <linux/blk-mq.h>
#include <linux/mount.h>
#include <linux/dax.h>
@@ -1449,10 +1448,6 @@ int dm_calculate_queue_limits(struct dm_table *table,
zone_sectors = ti_limits.chunk_sectors;
}
- /* Stack chunk_sectors if target-specific splitting is required */
- if (ti->max_io_len)
- ti_limits.chunk_sectors = lcm_not_zero(ti->max_io_len,
- ti_limits.chunk_sectors);
/* Set I/O hints portion of queue limits */
if (ti->type->io_hints)
ti->type->io_hints(ti, &ti_limits);
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 98866e725f25..f7eb3d2964f3 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1039,15 +1039,18 @@ static sector_t max_io_len(struct dm_target *ti, sector_t sector)
sector_t max_len;
/*
- * Does the target need to split even further?
- * - q->limits.chunk_sectors reflects ti->max_io_len so
- * blk_max_size_offset() provides required splitting.
- * - blk_max_size_offset() also respects q->limits.max_sectors
+ * Does the target need to split IO even further?
+ * - varied (per target) IO splitting is a tenet of DM; this
+ * explains why stacked chunk_sectors based splitting via
+ * blk_max_size_offset() isn't possible here. So pass in
+ * ti->max_io_len to override stacked chunk_sectors.
*/
- max_len = blk_max_size_offset(ti->table->md->queue,
- target_offset);
- if (len > max_len)
- len = max_len;
+ if (ti->max_io_len) {
+ max_len = blk_max_size_offset(ti->table->md->queue,
+ target_offset, ti->max_io_len);
+ if (len > max_len)
+ len = max_len;
+ }
return len;
}
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 639cae2c158b..24ae504cf77d 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1073,11 +1073,12 @@ static inline unsigned int blk_queue_get_max_sectors(struct request_queue *q,
* file system requests.
*/
static inline unsigned int blk_max_size_offset(struct request_queue *q,
- sector_t offset)
+ sector_t offset,
+ unsigned int chunk_sectors)
{
- unsigned int chunk_sectors = q->limits.chunk_sectors;
-
- if (!chunk_sectors)
+ if (!chunk_sectors && q->limits.chunk_sectors)
+ chunk_sectors = q->limits.chunk_sectors;
+ else
return q->limits.max_sectors;
if (likely(is_power_of_2(chunk_sectors)))
@@ -1101,7 +1102,7 @@ static inline unsigned int blk_rq_get_max_sectors(struct request *rq,
req_op(rq) == REQ_OP_SECURE_ERASE)
return blk_queue_get_max_sectors(q, req_op(rq));
- return min(blk_max_size_offset(q, offset),
+ return min(blk_max_size_offset(q, offset, 0),
blk_queue_get_max_sectors(q, req_op(rq)));
}
