block: Generic bio chaining

This adds a generic mechanism for chaining bio completions. This is
going to be used for a bio_split() replacement, and it turns out to be
very useful in a fair amount of driver code - a fair number of drivers
were implementing this in their own roundabout ways, often painfully.

Note that this means it's no longer to call bio_endio() more than once
on the same bio! This can cause problems for drivers that save/restore
bi_end_io. Arguably they shouldn't be saving/restoring bi_end_io at all
- in all but the simplest cases they'd be better off just cloning the
bio, and immutable biovecs is making bio cloning cheaper. But for now,
we add a bio_endio_nodec() for these cases.

Signed-off-by: Kent Overstreet <kmo@daterainc.com>
Cc: Jens Axboe <axboe@kernel.dk>

1 files changed, 1 insertions, 1 deletions

diff --git a/drivers/md/bcache/io.c b/drivers/md/bcache/io.c
index 0f0ab659914d..522f95778443 100644
--- a/drivers/md/bcache/io.c
+++ b/drivers/md/bcache/io.c
@@ -133,7 +133,7 @@ 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(s->bio, 0);
+        bio_endio_nodec(s->bio, 0);
 
         closure_debug_destroy(&s->cl);
         mempool_free(s, s->p->bio_split_hook);