[PATCH for-4.2 v2 01/14] block: remove management of bi_remaining when restoring original bi_end_io

[Mike Snitzer <snitzer@redhat.com>]

Commit c4cf5261 ("bio: skip atomic inc/dec of ->bi_remaining for
non-chains") regressed all existing callers that followed this pattern:
 1) saving a bio's original bi_end_io
 2) wiring up an intermediate bi_end_io
 3) restoring the original bi_end_io from intermediate bi_end_io
 4) calling bio_endio() to execute the restored original bi_end_io

The regression was due to BIO_CHAIN only ever getting set if
bio_inc_remaining() is called.  For the above pattern it isn't set until
step 3 above (step 2 would've needed to establish BIO_CHAIN).  As such
the first bio_endio(), in step 2 above, never decremented __bi_remaining
before calling the intermediate bi_end_io -- leaving __bi_remaining with
the value 1 instead of 0.  When bio_inc_remaining() occurred during step
3 it brought it to a value of 2.  When the second bio_endio() was
called, in step 4 above, it should've called the original bi_end_io but
it didn't because there was an extra reference that wasn't dropped (due
to atomic operations being optimized away since BIO_CHAIN wasn't set
upfront).

Fix this issue by removing the __bi_remaining management complexity for
all callers that use the above pattern -- bio_chain() is the only
interface that _needs_ to be concerned with __bi_remaining.  For the
above pattern callers just expect the bi_end_io they set to get called!
Remove bio_endio_nodec() and also remove all bio_inc_remaining() calls
that aren't associated with the bio_chain() interface.

changes in v2:
Care is now taken to clear the BIO_CHAIN flag once ->__bi_remaining
drops to 0.  Also, the bio_inc_remaining() interface has moved local to
bio.c.

Fixes: c4cf5261 ("bio: skip atomic inc/dec of ->bi_remaining for non-chains")
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
---
 block/bio-integrity.c        |  4 ++--
 block/bio.c                  | 35 ++++++++++++++---------------------
 drivers/md/bcache/io.c       |  2 +-
 drivers/md/dm-cache-target.c |  6 ------
 drivers/md/dm-raid1.c        |  2 --
 drivers/md/dm-snap.c         |  1 -
 drivers/md/dm-thin.c         |  9 +++------
 drivers/md/dm-verity.c       |  2 +-
 fs/btrfs/disk-io.c           |  2 +-
 fs/btrfs/volumes.c           | 16 +++++-----------
 fs/btrfs/volumes.h           |  2 --
 include/linux/bio.h          | 12 ------------
 12 files changed, 27 insertions(+), 66 deletions(-)

diff --git a/block/bio-integrity.c b/block/bio-integrity.c
index 5cbd5d9..0436c21 100644
--- a/block/bio-integrity.c
+++ b/block/bio-integrity.c
@@ -361,7 +361,7 @@ static void bio_integrity_verify_fn(struct work_struct *work)
 
 	/* Restore original bio completion handler */
 	bio->bi_end_io = bip->bip_end_io;
-	bio_endio_nodec(bio, error);
+	bio_endio(bio, error);
 }
 
 /**
@@ -388,7 +388,7 @@ void bio_integrity_endio(struct bio *bio, int error)
 	 */
 	if (error) {
 		bio->bi_end_io = bip->bip_end_io;
-		bio_endio_nodec(bio, error);
+		bio_endio(bio, error);
 
 		return;
 	}
diff --git a/block/bio.c b/block/bio.c
index c2ff8a8..259197d 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -303,6 +303,17 @@ static void bio_chain_endio(struct bio *bio, int error)
 	bio_put(bio);
 }
 
+/*
+ * Increment chain count for the bio. Make sure the CHAIN flag update
+ * is visible before the raised count.
+ */
+static inline void bio_inc_remaining(struct bio *bio)
+{
+	bio->bi_flags |= (1 << BIO_CHAIN);
+	smp_mb__before_atomic();
+	atomic_inc(&bio->__bi_remaining);
+}
+
 /**
  * bio_chain - chain bio completions
  * @bio: the target bio
@@ -1756,8 +1767,10 @@ static inline bool bio_remaining_done(struct bio *bio)
 
 	BUG_ON(atomic_read(&bio->__bi_remaining) <= 0);
 
-	if (atomic_dec_and_test(&bio->__bi_remaining))
+	if (atomic_dec_and_test(&bio->__bi_remaining)) {
+		clear_bit(BIO_CHAIN, &bio->bi_flags);
 		return true;
+	}
 
 	return false;
 }
@@ -1809,26 +1822,6 @@ void bio_endio(struct bio *bio, int error)
 EXPORT_SYMBOL(bio_endio);
 
 /**
- * bio_endio_nodec - end I/O on a bio, without decrementing bi_remaining
- * @bio:	bio
- * @error:	error, if any
- *
- * For code that has saved and restored bi_end_io; thing hard before using this
- * function, probably you should've cloned the entire bio.
- **/
-void bio_endio_nodec(struct bio *bio, int error)
-{
-	/*
-	 * If it's not flagged as a chain, we are not going to dec the count
-	 */
-	if (bio_flagged(bio, BIO_CHAIN))
-		bio_inc_remaining(bio);
-
-	bio_endio(bio, error);
-}
-EXPORT_SYMBOL(bio_endio_nodec);
-
-/**
  * bio_split - split a bio
  * @bio:	bio to split
  * @sectors:	number of sectors to split from the front of @bio
diff --git a/drivers/md/bcache/io.c b/drivers/md/bcache/io.c
index fa028fa..cb64e64a 100644
--- a/drivers/md/bcache/io.c
+++ b/drivers/md/bcache/io.c
@@ -55,7 +55,7 @@ static void bch_bio_submit_split_done(struct closure *cl)
 
 	s->bio->bi_end_io = s->bi_end_io;
 	s->bio->bi_private = s->bi_private;
-	bio_endio_nodec(s->bio, 0);
+	bio_endio(s->bio, 0);
 
 	closure_debug_destroy(&s->cl);
 	mempool_free(s, s->p->bio_split_hook);
diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index 705eb7b..41b2594 100644
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -86,12 +86,6 @@ static void dm_unhook_bio(struct dm_hook_info *h, struct bio *bio)
 {
 	bio->bi_end_io = h->bi_end_io;
 	bio->bi_private = h->bi_private;
-
-	/*
-	 * Must bump bi_remaining to allow bio to complete with
-	 * restored bi_end_io.
-	 */
-	bio_inc_remaining(bio);
 }
 
 /*----------------------------------------------------------------*/
diff --git a/drivers/md/dm-raid1.c b/drivers/md/dm-raid1.c
index d6a1c09..743fa9b 100644
--- a/drivers/md/dm-raid1.c
+++ b/drivers/md/dm-raid1.c
@@ -1254,8 +1254,6 @@ static int mirror_end_io(struct dm_target *ti, struct bio *bio, int error)
 			dm_bio_restore(bd, bio);
 			bio_record->details.bi_bdev = NULL;
 
-			bio_inc_remaining(bio);
-
 			queue_bio(ms, bio, rw);
 			return DM_ENDIO_INCOMPLETE;
 		}
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 8bfeae2..7c82d3c 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -1478,7 +1478,6 @@ out:
 	if (full_bio) {
 		full_bio->bi_end_io = pe->full_bio_end_io;
 		full_bio->bi_private = pe->full_bio_private;
-		bio_inc_remaining(full_bio);
 	}
 	increment_pending_exceptions_done_count();
 
diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index 342dbda..e852602c 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -793,10 +793,9 @@ static void inc_remap_and_issue_cell(struct thin_c *tc,
 
 static void process_prepared_mapping_fail(struct dm_thin_new_mapping *m)
 {
-	if (m->bio) {
+	if (m->bio)
 		m->bio->bi_end_io = m->saved_bi_end_io;
-		bio_inc_remaining(m->bio);
-	}
+
 	cell_error(m->tc->pool, m->cell);
 	list_del(&m->list);
 	mempool_free(m, m->tc->pool->mapping_pool);
@@ -810,10 +809,8 @@ static void process_prepared_mapping(struct dm_thin_new_mapping *m)
 	int r;
 
 	bio = m->bio;
-	if (bio) {
+	if (bio)
 		bio->bi_end_io = m->saved_bi_end_io;
-		bio_inc_remaining(bio);
-	}
 
 	if (m->err) {
 		cell_error(pool, m->cell);
diff --git a/drivers/md/dm-verity.c b/drivers/md/dm-verity.c
index 66616db..bb9c6a0 100644
--- a/drivers/md/dm-verity.c
+++ b/drivers/md/dm-verity.c
@@ -459,7 +459,7 @@ static void verity_finish_io(struct dm_verity_io *io, int error)
 	bio->bi_end_io = io->orig_bi_end_io;
 	bio->bi_private = io->orig_bi_private;
 
-	bio_endio_nodec(bio, error);
+	bio_endio(bio, error);
 }
 
 static void verity_work(struct work_struct *w)
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 2ef9a4b..fbdbee4 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1745,7 +1745,7 @@ static void end_workqueue_fn(struct btrfs_work *work)
 	bio->bi_private = end_io_wq->private;
 	bio->bi_end_io = end_io_wq->end_io;
 	kmem_cache_free(btrfs_end_io_wq_cache, end_io_wq);
-	bio_endio_nodec(bio, error);
+	bio_endio(bio, error);
 }
 
 static int cleaner_kthread(void *arg)
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 8e8d1d1..dac77d4 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -5585,10 +5585,10 @@ int btrfs_rmap_block(struct btrfs_mapping_tree *map_tree,
 
 static inline void btrfs_end_bbio(struct btrfs_bio *bbio, struct bio *bio, int err)
 {
-	if (likely(bbio->flags & BTRFS_BIO_ORIG_BIO_SUBMITTED))
-		bio_endio_nodec(bio, err);
-	else
-		bio_endio(bio, err);
+	bio->bi_private = bbio->private;
+	bio->bi_end_io = bbio->end_io;
+	bio_endio(bio, err);
+
 	btrfs_put_bbio(bbio);
 }
 
@@ -5632,8 +5632,6 @@ static void btrfs_end_bio(struct bio *bio, int err)
 			bio = bbio->orig_bio;
 		}
 
-		bio->bi_private = bbio->private;
-		bio->bi_end_io = bbio->end_io;
 		btrfs_io_bio(bio)->mirror_num = bbio->mirror_num;
 		/* only send an error to the higher layers if it is
 		 * beyond the tolerance of the btrfs bio
@@ -5815,8 +5813,6 @@ static void bbio_error(struct btrfs_bio *bbio, struct bio *bio, u64 logical)
 		/* Shoud be the original bio. */
 		WARN_ON(bio != bbio->orig_bio);
 
-		bio->bi_private = bbio->private;
-		bio->bi_end_io = bbio->end_io;
 		btrfs_io_bio(bio)->mirror_num = bbio->mirror_num;
 		bio->bi_iter.bi_sector = logical >> 9;
 
@@ -5897,10 +5893,8 @@ int btrfs_map_bio(struct btrfs_root *root, int rw, struct bio *bio,
 		if (dev_nr < total_devs - 1) {
 			bio = btrfs_bio_clone(first_bio, GFP_NOFS);
 			BUG_ON(!bio); /* -ENOMEM */
-		} else {
+		} else
 			bio = first_bio;
-			bbio->flags |= BTRFS_BIO_ORIG_BIO_SUBMITTED;
-		}
 
 		submit_stripe_bio(root, bbio, bio,
 				  bbio->stripes[dev_nr].physical, dev_nr, rw,
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index ebc3133..cedae03 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -292,8 +292,6 @@ struct btrfs_bio_stripe {
 struct btrfs_bio;
 typedef void (btrfs_bio_end_io_t) (struct btrfs_bio *bio, int err);
 
-#define BTRFS_BIO_ORIG_BIO_SUBMITTED	(1 << 0)
-
 struct btrfs_bio {
 	atomic_t refs;
 	atomic_t stripes_pending;
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 7486ea1..f0291cf 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -427,7 +427,6 @@ static inline struct bio *bio_clone_kmalloc(struct bio *bio, gfp_t gfp_mask)
 }
 
 extern void bio_endio(struct bio *, int);
-extern void bio_endio_nodec(struct bio *, int);
 struct request_queue;
 extern int bio_phys_segments(struct request_queue *, struct bio *);
 
@@ -659,17 +658,6 @@ static inline struct bio *bio_list_get(struct bio_list *bl)
 }
 
 /*
- * Increment chain count for the bio. Make sure the CHAIN flag update
- * is visible before the raised count.
- */
-static inline void bio_inc_remaining(struct bio *bio)
-{
-	bio->bi_flags |= (1 << BIO_CHAIN);
-	smp_mb__before_atomic();
-	atomic_inc(&bio->__bi_remaining);
-}
-
-/*
  * bio_set is used to allow other portions of the IO system to
  * allocate their own private memory pools for bio and iovec structures.
  * These memory pools in turn all allocate from the bio_slab
-- 
2.3.2 (Apple Git-55)