Re: [PATCH v4 1/2] uio_hv_generic: Fix sysfs creation path for ring buffer

Naman Jain
2025-04-15T15:54:23Z

On 4/15/2025 8:40 PM, Greg Kroah-Hartman wrote:
> On Thu, Apr 10, 2025 at 11:38:46AM +0530, Naman Jain wrote:
>> On regular bootup, devices get registered to VMBus first, so when
>> uio_hv_generic driver for a particular device type is probed,
>> the device is already initialized and added, so sysfs creation in
>> uio_hv_generic probe works fine. However, when device is removed
>> and brought back, the channel rescinds and device again gets
>> registered to VMBus. However this time, the uio_hv_generic driver is
>> already registered to probe for that device and in this case sysfs
>> creation is tried before the device's kobject gets initialized
>> completely.
>>
>> Fix this by moving the core logic of sysfs creation for ring buffer,
>> from uio_hv_generic to HyperV's VMBus driver, where rest of the sysfs
>> attributes for the channels are defined. While doing that, make use
>> of attribute groups and macros, instead of creating sysfs directly,
>> to ensure better error handling and code flow.
>>
>> Problem path:
>> vmbus_process_offer (new offer comes for the VMBus device)
>> vmbus_add_channel_work
>> vmbus_device_register
>> |-> device_register
>> | |...
>> | |-> hv_uio_probe
>> | |...
>> | |-> sysfs_create_bin_file (leads to a warning as
>> | primary channel's kobject, which is used to
>> | create sysfs is not yet initialized)
>> |-> kset_create_and_add
>> |-> vmbus_add_channel_kobj (initialization of primary channel's
>> kobject happens later)
>>
>> Above code flow is sequential and the warning is always reproducible in
>> this path.
>>
>> Fixes: 9ab877a6ccf8 ("uio_hv_generic: make ring buffer attribute for primary channel")
>> Cc: stable@kernel.org
>> Suggested-by: Saurabh Sengar <ssengar@linux.microsoft.com>
>> Suggested-by: Michael Kelley <mhklinux@outlook.com>
>> Signed-off-by: Naman Jain <namjain@linux.microsoft.com>
>> ---
>> drivers/hv/hyperv_vmbus.h | 6 ++
>> drivers/hv/vmbus_drv.c | 110 ++++++++++++++++++++++++++++++++++-
>> drivers/uio/uio_hv_generic.c | 39 ++++++-------
>> include/linux/hyperv.h | 6 ++
>> 4 files changed, 138 insertions(+), 23 deletions(-)
>
> Always run checkpatch on a patch before submitting it for review :(
>

Hi Greg,
I verified again and I could not see checkpatch warnings with patch 1,2.
There was a warning regarding length of characters for link to previous
versions in the cover letter but I ignored it.

I tried on latest linux-next tip with this series fetched from lore
using b4. I'm sorry, if I am missing something, but can you please try
again.

Thanks,
Naman