[PATCH 0/8] ublk: don't dispatch to canceled io commands

[Ming Lei <tom.leiming@gmail.com>]

Hi,

Josef reported three ways in which ublk dispatches a request to a
canceled io command, which oopses on the NULL io->cmd in
ublk_queue_cmd() [1]:

1) STOP_DEV, then START_DEV
2) partial FETCH: a task fetches some tags and exits, then another task
   fetches the rest
3) user recovery: one queue's task exits before all queues are ready

This series fixes them in a simpler way, without extra locking in the
I/O path:

- patch 1: a FETCH round which saw a cancel stays canceling until the
  server is gone (2, 3)
- patch 2-3: an io command is marked cancelable before it is published
- patch 4-6: the release resets the FETCH round, also without a disk
  and under ub->mutex; STOP_DEV holds a reference on /dev/ublkcN while
  it cancels, so no START_DEV, FETCH or new server can slip in (1)
- patch 7-8: selftest

Tested with all ublk selftests, plus KASAN and lockdep.

[1] https://lore.kernel.org/linux-block/20260928-b4-ublk-cancel-stop-v1-0-4a4360232a46@toxicpanda.com/

Thanks,
Ming

Ming Lei (8):
  ublk: keep a canceled FETCH round canceling until the server is gone
  ublk: mark the io command cancelable before publishing it
  ublk: mark the batch fetch command cancelable before linking it
  ublk: reset the FETCH round in release also without a disk
  ublk: reset the FETCH round under ub->mutex
  ublk: let STOP_DEV cancel the server's commands before its release
  selftests: ublk: move the control command helpers into ctrl.c
  selftests: ublk: add test for going live over canceled io commands

 drivers/block/ublk_drv.c                      | 206 +++-
 tools/testing/selftests/ublk/.gitignore       |   1 +
 tools/testing/selftests/ublk/Makefile         |   6 +-
 tools/testing/selftests/ublk/ctrl.c           | 268 +++++
 tools/testing/selftests/ublk/kublk.c          | 271 -----
 tools/testing/selftests/ublk/kublk.h          |  32 +
 .../testing/selftests/ublk/test_generic_18.sh |  37 +
 .../selftests/ublk/ublk_cancel_ready.c        | 984 ++++++++++++++++++
 8 files changed, 1484 insertions(+), 321 deletions(-)
 create mode 100644 tools/testing/selftests/ublk/ctrl.c
 create mode 100755 tools/testing/selftests/ublk/test_generic_18.sh
 create mode 100644 tools/testing/selftests/ublk/ublk_cancel_ready.c

-- 
2.55.0