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dm: fix failure when empty flush's bi_sector points beyond the device end 

An empty flush bio can have arbitrary bi_sector. The commit 2b1c6d7a89
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 <mpatocka@redhat.com>
Fixes: 2b1c6d7a89 ("dm: optimize REQ_PREFLUSH with data when using the linear target")
Reported-by: Zdenek Kabelac <zkabelac@redhat.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
This commit is contained in:
Mikulas Patocka 2025-11-20 12:08:47 +01:00
parent a6ee8422b4
commit a612d24e85
1 changed files with 1 additions and 1 deletions
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2
drivers/md/dm.c
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@ -2005,7 +2005,7 @@ static void dm_split_and_process_bio(struct mapped_device *md,
* 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;