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

[Greg Kroah-Hartman]

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@xxxxxxxxxx
> Suggested-by: Saurabh Sengar <ssengar@xxxxxxxxxxxxxxxxxxx>
> Suggested-by: Michael Kelley <mhklinux@xxxxxxxxxxx>
> Signed-off-by: Naman Jain <namjain@xxxxxxxxxxxxxxxxxxx>
> ---
>  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 :(