[PATCHv6 0/3] vfio/mdev: Improve vfio/mdev core module

[Parav Pandit]

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 Improves the mdev create/remove sequence to match Linux
bus, device model
Patch-2 Avoid recreating remove file on stale device to eliminate
call trace
Patch-3 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:
---
v5->v6:
 - Fixed mdev leak on fail to acquire semaphore
 - Corrected access to accessed
 - Avoided using ret and directly checking try_lock result
v4->v5:
 - Addressed comments from Alex Williamson
 - Added comment around mdev_device_remove_common()
 - Added lockdep assert to catch any missing lock
 - Corrected 'system' to 'sequence' in 2nd patch commit log
 - Refactored mdev_device_remove_cb() to remove unused parent
 - Added Cornelia's Reviewed-by signature to already reviewed patches 1, 2.
v3->v4:
 - Addressed comments from Cornelia for unbalanced mutex_unlock
 - Correct typo of subsquent to subsequent in patch-1 commit log
 - Instead of using refcount and completion, using rwsem to synchronize
   between mdev creation/deletion and parent unregistration
v2->v3:
 - Addressed comment from Cornelia
 - Corrected several errors in commit log, updated commit log
 - Dropped already merged 7 patches
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 (3):
  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    | 135 +++++++++++++++----------------
 drivers/vfio/mdev/mdev_private.h |   4 +-
 drivers/vfio/mdev/mdev_sysfs.c   |   6 +-
 3 files changed, 68 insertions(+), 77 deletions(-)

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2.19.2