[PATCH v4 0/2] uio_hv_generic: Fix ring buffer sysfs creation path

Naman Jain
2025-04-10T06:08:59Z

Hi,
This patch series aims to address the sysfs creation issue for the ring
buffer by reorganizing the code. Additionally, it updates the ring sysfs
size to accurately reflect the actual ring buffer size, rather than a
fixed static value.

PFB change logs:

Changes since v3:
https://lore.kernel.org/all/20250328052745.1417-1-namjain@linux.microsoft.com/
* Addressed Michael's comments regarding handling of return value of
sysfs_update_group in uio_hv_generic.

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 | 39 +++++-------
include/linux/hyperv.h | 6 ++
4 files changed, 147 insertions(+), 23 deletions(-)

base-commit: 0af2f6be1b4281385b618cb86ad946eded089ac8
--
2.43.0