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 <mpatocka@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # 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;
}
--
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