On Tue, 30 Aug 2016, Ming Lei wrote:

On Tue, Aug 30, 2016 at 5:57 AM, Mikulas Patocka [off-list ref] wrote:

quoted

On Mon, 29 Aug 2016, Ming Lei wrote:

quoted

On Sat, Aug 27, 2016 at 11:09 PM, Mikulas Patocka [off-list ref] wrote:

quoted

But this patch won't work for device mapper, blk_bio_segment_split is
called from blk_queue_split and device mapper doesn't use blk_queue_split
(it can't because it frees queue->bio_split).

We still need these two patches:
https://www.redhat.com/archives/dm-devel/2016-May/msg00211.html
https://www.redhat.com/archives/dm-devel/2016-May/msg00210.html

About the 2nd patch, it might not be good enough because in theory
a small size bio still may include big bvecs, such as, each bvec points
to 512byte buffer, so strictly speaking the bvec number should
be checked instead of bio size.

Ming Lei

This is not a problem.

I meant the following code in your 2nd patch:

+ if (unlikely(bio->bi_iter.bi_size > BIO_MAX_SIZE) &&
+    (bio->bi_rw & (REQ_FLUSH | REQ_DISCARD | REQ_WRITE)) == REQ_WRITE)
+ dm_accept_partial_bio(bio, BIO_MAX_SIZE >> SECTOR_SHIFT);

And the check on .bi_size may not work.

kcryptd_crypt_write_convert calls:
crypt_alloc_buffer(io, io->base_bio->bi_iter.bi_size)

crypt_alloc_buffer does:
unsigned int nr_iovecs = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
clone = bio_alloc_bioset(GFP_NOIO, nr_iovecs, cc->bs);

So, if io->base_bio->bi_iter.bi_size <= BIO_MAX_SIZE, then nr_iovecs will 
be less or equal than BIO_MAX_PAGES and the function bio_alloc_bioset will 
succeed.

(BTW. BIO_MAX_SIZE was removed in the current kernel, we should use 
(BIO_MAX_PAGES << PAGE_SHIFT) instead).

Mikulas