block: remove management of bi_remaining when restoring original bi_end_io
authorMike Snitzer <snitzer@redhat.com>
Fri, 22 May 2015 13:14:03 +0000 (09:14 -0400)
committerJens Axboe <axboe@fb.com>
Fri, 22 May 2015 14:58:55 +0000 (08:58 -0600)
commit326e1dbb57368087a36607aaebe9795b8d5453e5
treebbc17b38188d4f2d45d255f1254d63494d37e1e4
parentb04a5636a665f5529fdf69ee7e5512156196f31c
block: remove management of bi_remaining when restoring original bi_end_io

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.

Also, the bio_inc_remaining() interface has been moved local to bio.c.

Fixes: c4cf5261 ("bio: skip atomic inc/dec of ->bi_remaining for non-chains")
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
12 files changed:
block/bio-integrity.c
block/bio.c
drivers/md/bcache/io.c
drivers/md/dm-cache-target.c
drivers/md/dm-raid1.c
drivers/md/dm-snap.c
drivers/md/dm-thin.c
drivers/md/dm-verity.c
fs/btrfs/disk-io.c
fs/btrfs/volumes.c
fs/btrfs/volumes.h
include/linux/bio.h