[PATCHv2 00/10] vfio/mdev: Improve vfio/mdev core module

[Parav Pandit <parav@mellanox.com>]

As we would like to use mdev subsystem for wider use case as
discussed in [1], [2] apart from an offline discussion.
This use case is also discussed with wider forum in [4] in track
'Lightweight NIC HW functions for container offload use cases'.

This series is prep-work and improves vfio/mdev module in following ways.

Patch-1 Fixes releasing parent dev reference during error unwinding
        mdev parent registration.
Patch-2 Simplifies mdev device for unused kref.
Patch-3 Drops redundant extern prefix of exported symbols.
Patch-4 Returns right error code from vendor driver.
Patch-5 Fixes to use right sysfs remove sequence.
Patch-6 Fixes removing all child devices if one of them fails.
Patch-7 Remove unnecessary inline
Patch-8 Improve the mdev create/remove sequence to match Linux
        bus, device model
Patch-9 Avoid recreating remove file on stale device to
        eliminate call trace
Patch-10 Fix race conditions of create/remove with parent removal
This is improved version than using srcu as srcu can take
seconds to minutes.

This series is tested using
(a) mtty with VM using vfio_mdev driver for positive tests and
device removal while device in use by VM using vfio_mdev driver

(b) mlx5 core driver using RFC patches [3] and internal patches.
Internal patches are large and cannot be combined with this
prep-work patches. It will posted once prep-work completes.

[1] https://www.spinics.net/lists/netdev/msg556978.html
[2] https://lkml.org/lkml/2019/3/7/696
[3] https://lkml.org/lkml/2019/3/8/819
[4] https://netdevconf.org/0x13/session.html?workshop-hardware-offload

---
Changelog:
---
v1->v2:
 - Addressed comments from Alex
 - Rebased
 - Inserted the device checking loop in Patch-6 as original code
 - Added patch 7 to 10
 - Added fixes for race condition in create/remove with parent removal
   Patch-10 uses simplified refcount and completion, instead of srcu
   which might take seconds to minutes on busy system.
 - Added fix for device create/remove sequence to match
   Linux device, bus model
v0->v1:
 - Dropped device placement on bus sequence patch for this series
 - Addressed below comments from Alex, Kirti, Maxim.
 - Added Review-by tag for already reviewed patches.
 - Dropped incorrect patch of put_device().
 - Corrected Fixes commit tag for sysfs remove sequence fix
 - Split last 8th patch to smaller refactor and fixes patch
 - Following coding style commenting format
 - Fixed accidental delete of mutex_lock in mdev_unregister_device
 - Renamed remove helped to mdev_device_remove_common().
 - Rebased for uuid/guid change

Parav Pandit (10):
  vfio/mdev: Avoid release parent reference during error path
  vfio/mdev: Removed unused kref
  vfio/mdev: Drop redundant extern for exported symbols
  vfio/mdev: Avoid masking error code to EBUSY
  vfio/mdev: Follow correct remove sequence
  vfio/mdev: Fix aborting mdev child device removal if one fails
  vfio/mdev: Avoid inline get and put parent helpers
  vfio/mdev: Improve the create/remove sequence
  vfio/mdev: Avoid creating sysfs remove file on stale device removal
  vfio/mdev: Synchronize device create/remove with parent removal

 drivers/vfio/mdev/mdev_core.c    | 162 +++++++++++++------------------
 drivers/vfio/mdev/mdev_private.h |   9 +-
 drivers/vfio/mdev/mdev_sysfs.c   |   8 +-
 include/linux/mdev.h             |  21 ++--
 4 files changed, 89 insertions(+), 111 deletions(-)

-- 
2.19.2