dm: remove nr_iovecs parameter from alloc_tio()

alloc_tio() uses bio_alloc_bioset() to allocate a clone-bio for a bio.
alloc_tio() takes the number of bvecs to allocate for the clone-bio.
However, with v3.14's immutable biovec changes DM now uses
__bio_clone_fast() and no longer needs to allocate bvecs.

In practice, the 'nr_iovecs' passed to alloc_tio() is always effectively
0.  __clone_and_map_simple_bio() looked like it was passing non-zero
nr_iovecs, but its value was always within the range of inline bvecs and
no allocation actually happened.  If allocation happened, the BUG_ON() in
__bio_clone_fast() would've triggered.

Remove the nr_iovecs parameter from alloc_tio() to prevent possible
future bio_alloc_bioset() mis-use of a new bioset interface that will no
longer allow bvecs to be allocated.

Also fix extra whitespace before the __bio_clone_fast() call in
__clone_and_map_simple_bio().

Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

1 files changed, 5 insertions, 10 deletions

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 32b958dbc499..0b9de07d585b 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1249,13 +1249,13 @@ static void clone_bio(struct dm_target_io *tio, struct bio *bio,
 }
 
 static struct dm_target_io *alloc_tio(struct clone_info *ci,
-                                      struct dm_target *ti, int nr_iovecs,
+                                      struct dm_target *ti,
                                       unsigned target_bio_nr)
 {
         struct dm_target_io *tio;
         struct bio *clone;
 
-        clone = bio_alloc_bioset(GFP_NOIO, nr_iovecs, ci->md->bs);
+        clone = bio_alloc_bioset(GFP_NOIO, 0, ci->md->bs);
         tio = container_of(clone, struct dm_target_io, clone);
 
         tio->io = ci->io;
@@ -1269,17 +1269,12 @@ static void __clone_and_map_simple_bio(struct clone_info *ci,
                                        struct dm_target *ti,
                                        unsigned target_bio_nr, unsigned *len)
 {
-        struct dm_target_io *tio = alloc_tio(ci, ti, ci->bio->bi_max_vecs, target_bio_nr);
+        struct dm_target_io *tio = alloc_tio(ci, ti, target_bio_nr);
         struct bio *clone = &tio->clone;
 
         tio->len_ptr = len;
 
-        /*
-         * Discard requests require the bio's inline iovecs be initialized.
-         * ci->bio->bi_max_vecs is BIO_INLINE_VECS anyway, for both flush
-         * and discard, so no need for concern about wasted bvec allocations.
-         */
-         __bio_clone_fast(clone, ci->bio);
+        __bio_clone_fast(clone, ci->bio);
         if (len)
                 bio_setup_sector(clone, ci->sector, *len);
 
@@ -1322,7 +1317,7 @@ static void __clone_and_map_data_bio(struct clone_info *ci, struct dm_target *ti
                 num_target_bios = ti->num_write_bios(ti, bio);
 
         for (target_bio_nr = 0; target_bio_nr < num_target_bios; target_bio_nr++) {
-                tio = alloc_tio(ci, ti, 0, target_bio_nr);
+                tio = alloc_tio(ci, ti, target_bio_nr);
                 tio->len_ptr = len;
                 clone_bio(tio, bio, sector, *len);
                 __map_bio(tio);