dm io: respect BIO_MAX_PAGES limit

dm-io calls bio_get_nr_vecs to get the maximum number of pages to use
for a given device.  It allocates one additional bio_vec to use
internally but failed to respect BIO_MAX_PAGES, so fix this.

This was the likely cause of:
  https://bugzilla.redhat.com/show_bug.cgi?id=173153

Cc: stable@kernel.org
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/md/dm-io.c b/drivers/md/dm-io.c
index f14813be4eff..36e2b5e46a6b 100644
--- a/drivers/md/dm-io.c
+++ b/drivers/md/dm-io.c
@@ -292,6 +292,8 @@ static void do_region(int rw, unsigned region, struct dm_io_region *where,
                                              (PAGE_SIZE >> SECTOR_SHIFT));
                 num_bvecs = 1 + min_t(int, bio_get_nr_vecs(where->bdev),
                                       num_bvecs);
+                if (unlikely(num_bvecs > BIO_MAX_PAGES))
+                        num_bvecs = BIO_MAX_PAGES;
                 bio = bio_alloc_bioset(GFP_NOIO, num_bvecs, io->client->bios);
                 bio->bi_sector = where->sector + (where->count - remaining);
                 bio->bi_bdev = where->bdev;