[PATCH v3 0/2] uio_hv_generic: Fix ring buffer sysfs creation path

[Naman Jain <namjain@linux.microsoft.com>]

Hi,
PFB change logs:

Changes since v2:
https://lore.kernel.org/all/20250318061558.3294-1-namjain@linux.microsoft.com/
Addressed Greg's comments:
* Split the original patch into two.
* Updated the commit message to explain the problem scenario.
* Added comments for new APIs in the kerneldoc format.
* Highlighted potential race conditions and explained why sysfs should not be created in the
  driver probe.

* Made minor changes to how the sysfs_update_group return value is handled.

Changes since v1:
https://lore.kernel.org/all/20250225052001.2225-1-namjain@linux.microsoft.com/
* Fixed race condition in setting channel->mmap_ring_buffer by
  introducing a new variable for visibility of sysfs (addressed Greg's
  comments)
* Used binary attribute fields instead of regular ones for initializing attribute_group.
* Make size of ring sysfs dynamic based on actual ring buffer's size.
* Preferred to keep mmap function in uio_hv_generic to give more control over ring's
  mmap functionality, since this is specific to uio_hv_generic driver.
* Remove spurious warning during sysfs creation in uio_hv_generic probe.
* Added comments in a couple of places.

Changes since RFC patch:
https://lore.kernel.org/all/20250214064351.8994-1-namjain@linux.microsoft.com/
* Different approach to solve the problem is proposed (credits to
  Michael Kelley).
* Core logic for sysfs creation moved out of uio_hv_generic, to VMBus
  drivers where rest of the sysfs attributes for a VMBus channel
  are defined. (addressed Greg's comments)
* Used attribute groups instead of sysfs_create* functions, and bundled
  ring attribute with other attributes for the channel sysfs.  

Error logs:

[   35.574120] ------------[ cut here ]------------
[   35.574122] WARNING: CPU: 0 PID: 10 at fs/sysfs/file.c:591 sysfs_create_bin_file+0x81/0x90
[   35.574168] Workqueue: hv_pri_chan vmbus_add_channel_work
[   35.574172] RIP: 0010:sysfs_create_bin_file+0x81/0x90
[   35.574197] Call Trace:
[   35.574199]  <TASK>
[   35.574200]  ? show_regs+0x69/0x80
[   35.574217]  ? __warn+0x8d/0x130
[   35.574220]  ? sysfs_create_bin_file+0x81/0x90
[   35.574222]  ? report_bug+0x182/0x190
[   35.574225]  ? handle_bug+0x5b/0x90
[   35.574244]  ? exc_invalid_op+0x19/0x70
[   35.574247]  ? asm_exc_invalid_op+0x1b/0x20
[   35.574252]  ? sysfs_create_bin_file+0x81/0x90
[   35.574255]  hv_uio_probe+0x1e7/0x410 [uio_hv_generic]
[   35.574271]  vmbus_probe+0x3b/0x90
[   35.574275]  really_probe+0xf4/0x3b0
[   35.574279]  __driver_probe_device+0x8a/0x170
[   35.574282]  driver_probe_device+0x23/0xc0
[   35.574285]  __device_attach_driver+0xb5/0x140
[   35.574288]  ? __pfx___device_attach_driver+0x10/0x10
[   35.574291]  bus_for_each_drv+0x86/0xe0
[   35.574294]  __device_attach+0xc1/0x200
[   35.574297]  device_initial_probe+0x13/0x20
[   35.574315]  bus_probe_device+0x99/0xa0
[   35.574318]  device_add+0x647/0x870
[   35.574320]  ? hrtimer_init+0x28/0x70
[   35.574323]  device_register+0x1b/0x30
[   35.574326]  vmbus_device_register+0x83/0x130
[   35.574328]  vmbus_add_channel_work+0x135/0x1a0
[   35.574331]  process_one_work+0x177/0x340
[   35.574348]  worker_thread+0x2b2/0x3c0
[   35.574350]  kthread+0xe3/0x1f0
[   35.574353]  ? __pfx_worker_thread+0x10/0x10
[   35.574356]  ? __pfx_kthread+0x10/0x10

Regards,
Naman

Naman Jain (2):
  uio_hv_generic: Fix sysfs creation path for ring buffer
  Drivers: hv: Make the sysfs node size for the ring buffer dynamic

 drivers/hv/hyperv_vmbus.h    |   6 ++
 drivers/hv/vmbus_drv.c       | 119 ++++++++++++++++++++++++++++++++++-
 drivers/uio/uio_hv_generic.c |  33 ++++------
 include/linux/hyperv.h       |   6 ++
 4 files changed, 143 insertions(+), 21 deletions(-)


base-commit: db8da9da41bced445077925f8a886c776a47440c
-- 
2.34.1