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Subject[PATCH 5.0 111/117] dm: revert 8f50e358153d ("dm: limit the max bio size as BIO_MAX_PAGES * PAGE_SIZE")
From: Mikulas Patocka <>

commit 75ae193626de3238ca5fb895868ec91c94e63b1b upstream.

The limit was already incorporated to dm-crypt with commit 4e870e948fba
("dm crypt: fix error with too large bios"), so we don't need to apply
it globally to all targets. The quantity BIO_MAX_PAGES * PAGE_SIZE is
wrong anyway because the variable ti->max_io_len it is supposed to be in
the units of 512-byte sectors not in bytes.

Reduction of the limit to 1048576 sectors could even cause data
corruption in rare cases - suppose that we have a dm-striped device with
stripe size 768MiB. The target will call dm_set_target_max_io_len with
the value 1572864. The buggy code would reduce it to 1048576. Now, the
dm-core will errorneously split the bios on 1048576-sector boundary
insetad of 1572864-sector boundary and pass these stripe-crossing bios
to the striped target.

Cc: # v4.16+
Fixes: 8f50e358153d ("dm: limit the max bio size as BIO_MAX_PAGES * PAGE_SIZE")
Signed-off-by: Mikulas Patocka <>
Acked-by: Ming Lei <>
Signed-off-by: Mike Snitzer <>
Signed-off-by: Greg Kroah-Hartman <>

drivers/md/dm.c | 10 +---------
1 file changed, 1 insertion(+), 9 deletions(-)

--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1060,15 +1060,7 @@ int dm_set_target_max_io_len(struct dm_t
return -EINVAL;

- /*
- * BIO based queue uses its own splitting. When multipage bvecs
- * is switched on, size of the incoming bio may be too big to
- * be handled in some targets, such as crypt.
- *
- * When these targets are ready for the big bio, we can remove
- * the limit.
- */
- ti->max_io_len = min_t(uint32_t, len, BIO_MAX_PAGES * PAGE_SIZE);
+ ti->max_io_len = (uint32_t) len;

return 0;

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