Currently, `scsi_debug` only supported a maximum `sector_size` of 4096
bytes. However, on systems with a `PAGE_SIZE` greater than 4KB, some
`throtl` tests (002, 003, and 007) attempt to load `scsi_debug`
with `sector_size=$PAGE_SIZE`.

This mismatch causes `scsi_debug` module loading to fail, resulting in
test failures such as:

throtl/003 (sdebug) (bps limit over IO split)                [failed]
    runtime  0.147s  ...  0.146s
    --- tests/throtl/003.out    2025-04-04 04:36:43.175999880 +0800
    +++ /root/blktests/results/nodev_sdebug/throtl/003.out.bad  2025-11-16 09:26:07.287964459 +0800
    @@ -1,4 +1,3 @@
     Running throtl/003
    -1
    -1
    -Test complete
    +modprobe: ERROR: could not insert 'scsi_debug': Invalid argument
    +Loading scsi_debug dev_size_mb=1024 sector_size=65536 failed

To address this, introduce a `fixup_sedebug_sector_size` helper function.
This function checks the requested `sector_size` for `scsi_debug`. If the
value exceeds 4096, it defaults to a supported value of 2048 to ensure
successful module loading and test execution on hosts with larger
`PAGE_SIZE`.

Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
---
 tests/throtl/rc | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/tests/throtl/rc b/tests/throtl/rc
index d1afefd..fd83fb9 100644
--- a/tests/throtl/rc
+++ b/tests/throtl/rc
@@ -41,6 +41,17 @@ _set_throtl_blkdev_type() {
 	COND_DESC="${throtl_blkdev_type}"
 }
 
+# Only 512, 1024, 2048, 4096 are supported, see drivers/scsi/scsi_debug.c
+fixup_sdebug_sector_size() {
+	local sector_size=$1
+
+	if [[ $sector_size -gt 4096 ]]; then
+		echo 2048
+	else
+		echo $sector_size
+	fi
+}
+
 # Prepare null_blk or scsi_debug device to test, based on throtl_blkdev_type.
 _configure_throtl_blkdev() {
 	local sector_size=0 memory_backed=0
@@ -76,7 +87,8 @@ _configure_throtl_blkdev() {
 		;;
 	sdebug)
 		args=(dev_size_mb=1024)
-		((sector_size)) && args+=(sector_size="${sector_size}")
+		((sector_size)) &&
+		args+=(sector_size="$(fixup_sdebug_sector_size $sector_size)")
 		if _configure_scsi_debug "${args[@]}"; then
 			THROTL_DEV=${SCSI_DEBUG_DEVICES[0]}
 			return
-- 
2.44.0