The limit was already incorporated to dm-crypt (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. Signed-off-by: Mikulas Patocka <[email protected]> Cc: [email protected] # v4.16+ Fixes: 8f50e358153d ("dm: limit the max bio size as BIO_MAX_PAGES * PAGE_SIZE") --- drivers/md/dm.c | 10 +--------- 1 file changed, 1 insertion(+), 9 deletions(-) Index: linux-2.6/drivers/md/dm.c =================================================================== --- linux-2.6.orig/drivers/md/dm.c 2019-03-18 10:28:50.000000000 +0100 +++ linux-2.6/drivers/md/dm.c 2019-03-21 19:49:23.000000000 +0100 @@ -1042,15 +1042,7 @@ 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; } -- dm-devel mailing list [email protected] https://www.redhat.com/mailman/listinfo/dm-devel
