On 11/20/25 3:08 AM, Mikulas Patocka wrote:
An empty flush bio can have arbitrary bi_sector. The commit 2b1c6d7a890a
introduced a regression that device mapper would fail an empty flush bio
with -EIO if the sector pointed beyond the end of the device.
The commit introduced an optimization, that optimization would pass
flushes to __split_and_process_bio and __split_and_process_bio is not
prepared to handle empty bios. Fix this bug by passing only non-empty
flushes to __split_and_process_bio - non-empty flushes must have valid
bi_sector. Empty bios will go through __send_empty_flush, as they did
before the optimization.
This problem can be reproduced by running the lvm2 test:
make check_local T=lvconvert-thin.sh LVM_TEST_PREFER_BRD=0
Signed-off-by: Mikulas Patocka <[email protected]>
Fixes: 2b1c6d7a890a ("dm: optimize REQ_PREFLUSH with data when using the linear
target")
Reported-by: Zdenek Kabelac <[email protected]>
---
drivers/md/dm.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
Index: linux-2.6/drivers/md/dm.c
===================================================================
--- linux-2.6.orig/drivers/md/dm.c 2025-11-19 15:08:07.000000000 +0100
+++ linux-2.6/drivers/md/dm.c 2025-11-19 15:08:35.000000000 +0100
@@ -2005,7 +2005,7 @@ static void dm_split_and_process_bio(str
* linear target or multiple linear targets pointing to the same
* device), we can send the flush with data directly to it.
*/
- if (map->flush_bypasses_map) {
+ if (bio->bi_iter.bi_size && map->flush_bypasses_map) {
struct list_head *devices = dm_table_get_devices(map);
if (devices->next == devices->prev)
goto send_preflush_with_data;
Reviewed-by: Bart Van Assche <[email protected]>
