static struct bio *clone_bio(struct bio *bio, sector_t sector,
              unsigned short idx, unsigned short bv_count,
              unsigned int len, struct bio_set *bs)
{
   struct bio *clone;

   clone = bio_alloc_bioset(GFP_NOIO, bio->bi_max_vecs, bs);
   __bio_clone(clone, bio);
   clone->bi_destructor = dm_bio_destructor;
   clone->bi_sector = sector;
   clone->bi_idx = idx;
   clone->bi_vcnt = idx + bv_count;
   clone->bi_size = to_bytes(len);
   clone->bi_flags &= ~(1 << BIO_SEG_VALID);

   return clone;
}

There is a possibility of NULL being returned from bio_alloc_bioset. 
Although unlikely, it could crash the kernel.

If required, I have attached a patch (created on linux-2.6.23.9).

--Sumit