[RFC v2 00/17] bio cleanups

[Andreas Gruenbacher <agruenba@redhat.com>]

Hello,

we are not quite careful enough about setting bio->bi_status in all
places (see BACKGROUND below).  This patch queue tries to fix this by
systematically eliminating the direct assignments to bi_status sprinkled
all throughout the code.  Please comment.

The patches are currently still based on v6.18.

GIT tree:
https://git.kernel.org/pub/scm/linux/kernel/git/gfs2/linux-gfs2.git/log/?h=bio-cleanups

The first version of this patch queue is avaliable here:
https://lore.kernel.org/linux-block/20251208121020.1780402-1-agruenba@redhat.com/

With these changes, only a few direct assignments to bio->bi_status
remain, in BTRFS and in MD, and SOME OF THOSE MAY BE UNSAFE.  Could the
maintainers of those subsystems please have a look?

Once the remaining direct assignments to bi_status are gone, we may want
to think about "write protecting" bi_status to prevent unintended new
direct assignments from creeping back in.


BACKGROUND

'struct bio' objects start out with their bi_status field initialized to
BLK_STS_OK (0).  When the bio completes, that field needs to be left
unchanged in case of success, and set to a BLK_STS_* error code
otherwise.

This is important when bios are chained (bio_chain()) because then,
multiple execution contexts will race updating the same bi_status field.
When an execution context resets bi_status to BLK_STS_OK (0) during bio
completion, this could hide the error code of the adjacent bio in the
chain.

When more than a single bio fails in a chain, we know that the resulting
bi_status will not be BLK_STS_OK, but we don't know which of the status
error codes will survive.


CRYPTO FALLBACK (SATYA TANGIRALA?)

Related to chained bios but unrelated to setting bio->bi_status,
blk_crypto_fallback_encrypt_bio() in block/blk-crypto-fallback.c swaps
out bi_private and bi_end_io and reuses the same bio for downcalls, then
restores those fields in blk_crypto_fallback_decrypt_endio() before
calling bio_endio() again on the same bio.  This will at the very least
break with chained bios because it will mess up __bi_remaining.


Thanks,
Andreas

Andreas Gruenbacher (17):
  xfs: don't clobber bi_status in xfs_zone_alloc_and_submit
  bio: rename bio_chain arguments
  bio: use bio_io_error more often
  bio: add bio_set_status
  bio: use bio_set_status for BLK_STS_* status codes
  bio: do not check bio->bi_status before assigning to it
  block: consecutive blk_status_t error codes
  block: fix blk_status_to_{errno,str} inconsistency
  block: turn blk_errors array into a macro
  block: optimize blk_status <=> errno conversion
  bio: bio_set_status from non-zero errno
  bio: do not check bio->bi_status before assigning to it (part 2)
  xfs: use bio_set_status in xfs_zone_alloc_and_submit
  bio: switch to bio_set_status in submit_bio_noacct
  bio: never set bi_status to BLK_STS_OK during completion
  bio: never set bi_status to BLK_STS_OK during completion (part 2)
  bio: add bio_endio_status

 block/bio-integrity-auto.c       |   3 +-
 block/bio.c                      |  25 +++----
 block/blk-core.c                 | 123 ++++++++++++++++---------------
 block/blk-crypto-fallback.c      |  22 +++---
 block/blk-crypto-internal.h      |   2 +-
 block/blk-crypto.c               |   4 +-
 block/blk-merge.c                |   6 +-
 block/blk-mq.c                   |  10 +--
 block/fops.c                     |   6 +-
 block/t10-pi.c                   |   2 +-
 drivers/block/aoe/aoecmd.c       |   8 +-
 drivers/block/aoe/aoedev.c       |   2 +-
 drivers/block/drbd/drbd_int.h    |   3 +-
 drivers/block/drbd/drbd_req.c    |   7 +-
 drivers/block/ps3vram.c          |   3 +-
 drivers/block/zram/zram_drv.c    |   4 +-
 drivers/md/bcache/bcache.h       |   3 +-
 drivers/md/bcache/request.c      |   8 +-
 drivers/md/dm-cache-target.c     |   9 ++-
 drivers/md/dm-ebs-target.c       |   2 +-
 drivers/md/dm-flakey.c           |   2 +-
 drivers/md/dm-integrity.c        |  34 ++++-----
 drivers/md/dm-mpath.c            |   6 +-
 drivers/md/dm-pcache/dm_pcache.c |   3 +-
 drivers/md/dm-raid1.c            |   7 +-
 drivers/md/dm-thin.c             |   7 +-
 drivers/md/dm-vdo/data-vio.c     |   3 +-
 drivers/md/dm-verity-target.c    |   2 +-
 drivers/md/dm-writecache.c       |   7 +-
 drivers/md/dm-zoned-target.c     |   3 +-
 drivers/md/dm.c                  |   4 +-
 drivers/md/md.c                  |   8 +-
 drivers/md/raid1-10.c            |   3 +-
 drivers/md/raid1.c               |   2 +-
 drivers/md/raid10.c              |  20 +++--
 drivers/md/raid5.c               |   4 +-
 drivers/nvdimm/btt.c             |   4 +-
 drivers/nvdimm/pmem.c            |   4 +-
 fs/btrfs/bio.c                   |   8 +-
 fs/btrfs/direct-io.c             |   2 +-
 fs/btrfs/raid56.c                |   6 +-
 fs/crypto/bio.c                  |   2 +-
 fs/erofs/fileio.c                |   4 +-
 fs/erofs/fscache.c               |   8 +-
 fs/f2fs/data.c                   |   6 +-
 fs/f2fs/segment.c                |   3 +-
 fs/iomap/ioend.c                 |   3 +-
 fs/verity/verify.c               |   2 +-
 fs/xfs/xfs_aops.c                |   3 +-
 fs/xfs/xfs_zone_alloc.c          |   4 +-
 include/linux/bio.h              |  28 ++++++-
 include/linux/blk_types.h        |   2 +-
 include/linux/blkdev.h           |  18 ++++-
 53 files changed, 236 insertions(+), 238 deletions(-)

-- 
2.52.0