[PATCH RFC 0/6] bio_split() error handling rework

[John Garry <john.g.garry@oracle.com>]

bio_split() error handling could be improved as follows:
- Instead of returning NULL for an error - which is vague - return a
  PTR_ERR, which may hint what went wrong.
- Remove BUG_ON() calls - which are generally not preferred - and instead
  WARN and pass an error code back to the caller. Many callers of
  bio_split() don't check the return code. As such, for an error we would
  be getting a crash still from an invalid pointer dereference.

Most bio_split() callers don't check the return value. However, it could
be argued the bio_split() calls should not fail. So far I have just
fixed up the md RAID code to handle these errors, as that is my interest
now.

Sending as an RFC as unsure if this is the right direction.

The motivator for this series was initial md RAID atomic write support in
https://lore.kernel.org/linux-block/21f19b4b-4b83-4ca2-a93b-0a433741fd26@oracle.com/

There I wanted to ensure that we don't split an atomic write bio, and it
made more sense to handle this in bio_split() (instead of the bio_split()
caller).

John Garry (6):
  block: Rework bio_split() return value
  block: Error an attempt to split an atomic write in bio_split()
  block: Handle bio_split() errors in bio_submit_split()
  md/raid0: Handle bio_split() errors
  md/raid1: Handle bio_split() errors
  md/raid10: Handle bio_split() errors

 block/bio.c                 | 14 ++++++++++----
 block/blk-crypto-fallback.c |  2 +-
 block/blk-merge.c           |  5 +++++
 drivers/md/raid0.c          | 10 ++++++++++
 drivers/md/raid1.c          |  8 ++++++++
 drivers/md/raid10.c         | 18 ++++++++++++++++++
 6 files changed, 52 insertions(+), 5 deletions(-)

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2.31.1