dm-writecache doesn't work in pmem mode - mkfs.ext4 and the following
fsck.ext4 fail with data corruption reported.
The commit 7dd76d1feec7 ("dm: improve bio splitting and associated IO
accounting") introduced a latent bug in dm_accept_partial_bio - it set
tio->io->sectors = n_sectors;. This is incorrect, according to the
diagram in the source code at dm_accept_partial_bio, it should be the
size of regions 1+2, not the region 2 alone.
The latent bug become real bug with the commit 8b211aaccb91 ("dm: add two
stage requeue mechanism").
dm-writecache in pmem mode is the only target that actually advances bio
with bio_advance and then calls dm_accept_partial_bio (so, the region 1
is non-empty). All the other targets call dm_accept_partial_bio with
region 1 empty, so bug went unnoticed for so long.
Signed-off-by: Mikulas Patocka <[email protected]>
Assisted-by: Claude:claude-opus-5
Cc: [email protected]
Fixes: 8b211aaccb91 ("dm: add two stage requeue mechanism")
---
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
+++ linux-2.6/drivers/md/dm.c
@@ -1350,7 +1350,7 @@ void dm_accept_partial_bio(struct bio *b
* for accounting but it is being reduced so update accordingly.
*/
dm_io_set_flag(io, DM_IO_WAS_SPLIT);
- io->sectors = n_sectors;
+ io->sectors = *tio->len_ptr;
io->sector_offset = bio_sectors(io->orig_bio);
}
EXPORT_SYMBOL_GPL(dm_accept_partial_bio);
