[PATCH 00/27] block: cleanup direct access on .bi_vcnt & .bi_io_vec

[PATCH 00/27] block: cleanup direct access on .bi_vcnt & .bi_io_vec

[Ming Lei]

Hi Guys,

It is always not a good practice to access bio->bi_vcnt and
bio->bi_io_vec from drivers directly. Also this kind of direct
access will cause trouble when converting to multipage bvecs.

The 1st patch introduces the following 4 bio helpers which can be
used inside drivers for avoiding direct access to .bi_vcnt and .bi_io_vec.

	bio_pages()
	bio_is_full()
	bio_get_base_vec()
	bio_set_vec_table()

Both bio_pages() and bio_is_full() can be easy to convert to
multipage bvecs.

For bio_get_base_vec() and bio_set_vec_table(), they are often used
during initializing a new bio or in case of single bvec bio. With the
two new helpers, it becomes quite easy to audit access to .bi_io_vec
and .bi_vcnt.

Most of the other patches use the 4 helpers to clean up most of direct
access to .bi_vcnt and .bi_io_vec from drivers, except for MD and btrfs,
which two subsystems will be done in the future. 

Also bio_add_page() is used in floppy, dm-crypt and fs/logfs to
avoiding direct access to .bi_vcnt & .bi_io_vec.

Thanks,
Ming

Ming Lei (27):
  block: bio: introduce 4 helpers for cleanup
  block: drbd: use bio_get_base_vec() to retrieve the 1st bvec
  block: drbd: remove impossible failure handling
  block: loop: use bio_get_base_vec() to retrive bvec table
  block: pktcdvd: use bio_get_base_vec() to retrive bvec table
  block: floppy: use bio_set_vec_table()
  block: floppy: use bio_add_page()
  staging: lustre: avoid to use bio->bi_vcnt directly
  target: use bio_is_full()
  bcache: debug: avoid to access .bi_io_vec directly
  bcache: io.c: use bio_set_vec_table
  bcache: journal.c: use bio_set_vec_table()
  bcache: movinggc: use bio_set_vec_table()
  bcache: writeback: use bio_set_vec_table()
  bcache: super: use bio_set_vec_table()
  bcache: super: use bio_get_base_vec
  dm: crypt: use bio_add_page()
  dm: dm-io.c: use bio_get_base_vec()
  dm: dm.c: replace 'bio->bi_vcnt == 1' with !bio_multiple_segments
  dm: dm-bufio.c: use bio_set_vec_table()
  fs: logfs: use bio_set_vec_table()
  fs: logfs: convert to bio_add_page() in sync_request()
  fs: logfs: use bio_add_page() in __bdev_writeseg()
  fs: logfs: use bio_add_page() in do_erase()
  fs: logfs: remove unnecesary check
  kernel/power/swap.c: use bio_get_base_vec()
  mm: page_io.c: use bio_get_base_vec()

 drivers/block/drbd/drbd_bitmap.c            |   4 +-
 drivers/block/drbd/drbd_receiver.c          |  14 +---
 drivers/block/floppy.c                      |   9 +--
 drivers/block/loop.c                        |   5 +-
 drivers/block/pktcdvd.c                     |   3 +-
 drivers/md/bcache/debug.c                   |  11 ++-
 drivers/md/bcache/io.c                      |   3 +-
 drivers/md/bcache/journal.c                 |   3 +-
 drivers/md/bcache/movinggc.c                |   6 +-
 drivers/md/bcache/super.c                   |  28 +++++---
 drivers/md/bcache/writeback.c               |   4 +-
 drivers/md/dm-bufio.c                       |   3 +-
 drivers/md/dm-crypt.c                       |   8 +--
 drivers/md/dm-io.c                          |   7 +-
 drivers/md/dm.c                             |   3 +-
 drivers/staging/lustre/lustre/llite/lloop.c |   9 +--
 drivers/target/target_core_pscsi.c          |   2 +-
 fs/logfs/dev_bdev.c                         | 107 +++++++++++-----------------
 include/linux/bio.h                         |  28 ++++++++
 kernel/power/swap.c                         |  10 ++-
 mm/page_io.c                                |  18 ++++-
 21 files changed, 156 insertions(+), 129 deletions(-)

-- 
1.9.1

[PATCH 10/27] bcache: debug: avoid to access .bi_io_vec directly

[Ming Lei]

Instead we use standard iterator way to do that.

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
---
 drivers/md/bcache/debug.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/md/bcache/debug.c b/drivers/md/bcache/debug.c
index 8b1f1d5..d1ad49d 100644
--- a/drivers/md/bcache/debug.c
+++ b/drivers/md/bcache/debug.c
@@ -106,8 +106,8 @@ void bch_data_verify(struct cached_dev *dc, struct bio *bio)
 {
 	char name[BDEVNAME_SIZE];
 	struct bio *check;
-	struct bio_vec bv, *bv2;
-	struct bvec_iter iter;
+	struct bio_vec bv, cbv, *bv2;
+	struct bvec_iter iter, citer = { 0 };
 	int i;
 
 	check = bio_clone(bio, GFP_NOIO);
@@ -119,9 +119,13 @@ void bch_data_verify(struct cached_dev *dc, struct bio *bio)
 
 	submit_bio_wait(READ_SYNC, check);
 
+	citer.bi_size = UINT_MAX;
 	bio_for_each_segment(bv, bio, iter) {
 		void *p1 = kmap_atomic(bv.bv_page);
-		void *p2 = page_address(check->bi_io_vec[iter.bi_idx].bv_page);
+		void *p2;
+
+		cbv = bio_iter_iovec(check, citer);
+		p2 = page_address(cbv.bv_page);
 
 		cache_set_err_on(memcmp(p1 + bv.bv_offset,
 					p2 + bv.bv_offset,
@@ -132,6 +136,7 @@ void bch_data_verify(struct cached_dev *dc, struct bio *bio)
 				 (uint64_t) bio->bi_iter.bi_sector);
 
 		kunmap_atomic(p1);
+		bio_advance_iter(check, &citer, bv.bv_len);
 	}
 
 	bio_for_each_segment_all(bv2, check, i)
-- 
1.9.1

[PATCH 11/27] bcache: io.c: use bio_set_vec_table

[Ming Lei]

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
---
 drivers/md/bcache/io.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/md/bcache/io.c b/drivers/md/bcache/io.c
index 86a0bb8..1c48462 100644
--- a/drivers/md/bcache/io.c
+++ b/drivers/md/bcache/io.c
@@ -26,8 +26,7 @@ struct bio *bch_bbio_alloc(struct cache_set *c)
 
 	bio_init(bio);
 	bio->bi_flags		|= BIO_POOL_NONE << BIO_POOL_OFFSET;
-	bio->bi_max_vecs	 = bucket_pages(c);
-	bio->bi_io_vec		 = bio->bi_inline_vecs;
+	bio_set_vec_table(bio, bio->bi_inline_vecs, bucket_pages(c));
 
 	return bio;
 }
-- 
1.9.1

[PATCH 12/27] bcache: journal.c: use bio_set_vec_table()

[Ming Lei]

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
---
 drivers/md/bcache/journal.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/md/bcache/journal.c b/drivers/md/bcache/journal.c
index 29eba72..bf8924f 100644
--- a/drivers/md/bcache/journal.c
+++ b/drivers/md/bcache/journal.c
@@ -453,8 +453,7 @@ static void do_journal_discard(struct cache *ca)
 						ca->sb.d[ja->discard_idx]);
 		bio->bi_bdev		= ca->bdev;
 		bio->bi_rw		= REQ_WRITE|REQ_DISCARD;
-		bio->bi_max_vecs	= 1;
-		bio->bi_io_vec		= bio->bi_inline_vecs;
+		bio_set_vec_table(bio, bio->bi_inline_vecs, 1);
 		bio->bi_iter.bi_size	= bucket_bytes(ca);
 		bio->bi_end_io		= journal_discard_endio;
 
-- 
1.9.1

[PATCH 13/27] bcache: movinggc: use bio_set_vec_table()

[Ming Lei]

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
---
 drivers/md/bcache/movinggc.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/md/bcache/movinggc.c b/drivers/md/bcache/movinggc.c
index b929fc9..dbe5af2 100644
--- a/drivers/md/bcache/movinggc.c
+++ b/drivers/md/bcache/movinggc.c
@@ -85,10 +85,10 @@ static void moving_init(struct moving_io *io)
 	bio_set_prio(bio, IOPRIO_PRIO_VALUE(IOPRIO_CLASS_IDLE, 0));
 
 	bio->bi_iter.bi_size	= KEY_SIZE(&io->w->key) << 9;
-	bio->bi_max_vecs	= DIV_ROUND_UP(KEY_SIZE(&io->w->key),
-					       PAGE_SECTORS);
 	bio->bi_private		= &io->cl;
-	bio->bi_io_vec		= bio->bi_inline_vecs;
+	bio_set_vec_table(bio, bio->bi_inline_vecs,
+			  DIV_ROUND_UP(KEY_SIZE(&io->w->key),
+			  PAGE_SECTORS));
 	bch_bio_map(bio, NULL);
 }
 
-- 
1.9.1

[PATCH 14/27] bcache: writeback: use bio_set_vec_table()

[Ming Lei]

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
---
 drivers/md/bcache/writeback.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
index b9346cd..49a8f8a 100644
--- a/drivers/md/bcache/writeback.c
+++ b/drivers/md/bcache/writeback.c
@@ -112,9 +112,9 @@ static void dirty_init(struct keybuf_key *w)
 		bio_set_prio(bio, IOPRIO_PRIO_VALUE(IOPRIO_CLASS_IDLE, 0));
 
 	bio->bi_iter.bi_size	= KEY_SIZE(&w->key) << 9;
-	bio->bi_max_vecs	= DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS);
 	bio->bi_private		= w;
-	bio->bi_io_vec		= bio->bi_inline_vecs;
+	bio_set_vec_table(bio, bio->bi_inline_vecs,
+			  DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS));
 	bch_bio_map(bio, NULL);
 }
 
-- 
1.9.1

Re: [PATCH 11/27] bcache: io.c: use bio_set_vec_table

[Christoph Hellwig]

On Tue, Apr 05, 2016 at 07:56:56PM +0800, Ming Lei wrote:
> diff --git a/drivers/md/bcache/io.c b/drivers/md/bcache/io.c
> index 86a0bb8..1c48462 100644
> --- a/drivers/md/bcache/io.c
> +++ b/drivers/md/bcache/io.c
> @@ -26,8 +26,7 @@ struct bio *bch_bbio_alloc(struct cache_set *c)
>  
>  	bio_init(bio);
>  	bio->bi_flags		|= BIO_POOL_NONE << BIO_POOL_OFFSET;
> -	bio->bi_max_vecs	 = bucket_pages(c);
> -	bio->bi_io_vec		 = bio->bi_inline_vecs;
> +	bio_set_vec_table(bio, bio->bi_inline_vecs, bucket_pages(c));

All this bcache code needs to move away from bio_init on a bio
embedded in a driver private structure toward properly using
bio_alloc / bio_alloc_bioset.  That will also fix the crash
with bcache over md that Shaohua reported, so I'd suggest to fast
track this part of the series.

Re: [PATCH 11/27] bcache: io.c: use bio_set_vec_table

[Ming Lei]

On Tue, Apr 5, 2016 at 8:49 PM, Christoph Hellwig <hch@infradead.org> wrote:
> On Tue, Apr 05, 2016 at 07:56:56PM +0800, Ming Lei wrote:
>> diff --git a/drivers/md/bcache/io.c b/drivers/md/bcache/io.c
>> index 86a0bb8..1c48462 100644
>> --- a/drivers/md/bcache/io.c
>> +++ b/drivers/md/bcache/io.c
>> @@ -26,8 +26,7 @@ struct bio *bch_bbio_alloc(struct cache_set *c)
>>
>>       bio_init(bio);
>>       bio->bi_flags           |= BIO_POOL_NONE << BIO_POOL_OFFSET;
>> -     bio->bi_max_vecs         = bucket_pages(c);
>> -     bio->bi_io_vec           = bio->bi_inline_vecs;
>> +     bio_set_vec_table(bio, bio->bi_inline_vecs, bucket_pages(c));
>
> All this bcache code needs to move away from bio_init on a bio
> embedded in a driver private structure toward properly using
> bio_alloc / bio_alloc_bioset.  That will also fix the crash
> with bcache over md that Shaohua reported, so I'd suggest to fast
> track this part of the series.

I suggest to keep this usage for the following reasons:

- bio can be embedded into one biger instance, which is often allocated
dynamically, so one extra allocation for bio can be avoided.

- we should support arbitrary bio size by this way, at least bio_add_page()
supports this usage.  Also code gets lots of simplication with arbitrary bio
size support, such as prio_io(): bcache

BTW, the root cause for bcache crash still isn't clear now because
blk_bio_segment_split() should split big bio into proper size with
all queue's limits. Maybe the max segment limit isn't figured out correctly.

Thanks,
Ming Lei

Re: [PATCH 11/27] bcache: io.c: use bio_set_vec_table

[Christoph Hellwig]

On Tue, Apr 05, 2016 at 11:24:30PM +0800, Ming Lei wrote:
> - bio can be embedded into one biger instance, which is often allocated
> dynamically, so one extra allocation for bio can be avoided.

We can also do this the other way around with the bios front_pad,
which avoid the caller poking into bio details.

> - we should support arbitrary bio size by this way, at least bio_add_page()
> supports this usage.  Also code gets lots of simplication with arbitrary bio
> size support, such as prio_io(): bcache

There is no reason for not supporting huge bios in the core bio code,
in fact using bio_kmalloc you can already allocate huges bios
dynamically right now.  Except that you can't really use it, because the
layers below don't expect that.  Bios based drivers expect to be able to
call bio_clone and friends called on bios passed to them, and might
also make assumptions about the max number of bios segments for now.

> BTW, the root cause for bcache crash still isn't clear now because
> blk_bio_segment_split() should split big bio into proper size with
> all queue's limits. Maybe the max segment limit isn't figured out correctly.

The root cause is pretty simple:  The queue limits matter for request
based drivers, which are the only ones getting bios > BIO_MAX_PAGES
except for the buggy bcache use case.  You'll need to either adjust the
limit for all bio based drivers to or get rid of that one magic caller
not playing by the rules.

Re: [PATCH 11/27] bcache: io.c: use bio_set_vec_table

[Kent Overstreet]

On Tue, Apr 05, 2016 at 05:49:02AM -0700, Christoph Hellwig wrote:
> On Tue, Apr 05, 2016 at 07:56:56PM +0800, Ming Lei wrote:
> > diff --git a/drivers/md/bcache/io.c b/drivers/md/bcache/io.c
> > index 86a0bb8..1c48462 100644
> > --- a/drivers/md/bcache/io.c
> > +++ b/drivers/md/bcache/io.c
> > @@ -26,8 +26,7 @@ struct bio *bch_bbio_alloc(struct cache_set *c)
> >  
> >  	bio_init(bio);
> >  	bio->bi_flags		|= BIO_POOL_NONE << BIO_POOL_OFFSET;
> > -	bio->bi_max_vecs	 = bucket_pages(c);
> > -	bio->bi_io_vec		 = bio->bi_inline_vecs;
> > +	bio_set_vec_table(bio, bio->bi_inline_vecs, bucket_pages(c));
> 
> All this bcache code needs to move away from bio_init on a bio
> embedded in a driver private structure toward properly using
> bio_alloc / bio_alloc_bioset.  That will also fix the crash
> with bcache over md that Shaohua reported, so I'd suggest to fast
> track this part of the series.

Why?

bio_init() is a publicly exported function, it's always been one and bcache is
ot the only driver to use it directly.

bios with > BIO_MAX_PAGES bvecs is a separate issue; I would argue that the bug
is in md's queue_limits; it uses blk_set_stacking_limits() which sets
max_segments = USHRT_MAX, which is wrong if it's going to clone the biovec.