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

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Message-ID: <30593f68-05c6-407f-8b26-9e1f331cd33c@linux.microsoft.com>
Date: Tue, 15 Apr 2025 21:51:43 +0530
From: Naman Jain <namjain@...ux.microsoft.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: "K . Y . Srinivasan" <kys@...rosoft.com>,
 Haiyang Zhang <haiyangz@...rosoft.com>, Wei Liu <wei.liu@...nel.org>,
 Dexuan Cui <decui@...rosoft.com>,
 Stephen Hemminger <stephen@...workplumber.org>,
 linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
 stable@...nel.org, Saurabh Sengar <ssengar@...ux.microsoft.com>,
 Michael Kelley <mhklinux@...look.com>
Subject: Re: [PATCH v4 1/2] uio_hv_generic: Fix sysfs creation path for ring
 buffer



On 4/15/2025 9:44 PM, Greg Kroah-Hartman wrote:
> On Tue, Apr 15, 2025 at 09:24:16PM +0530, Naman Jain wrote:
>>
>>
>> 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@...nel.org
>>>> Suggested-by: Saurabh Sengar <ssengar@...ux.microsoft.com>
>>>> Suggested-by: Michael Kelley <mhklinux@...look.com>
>>>> Signed-off-by: Naman Jain <namjain@...ux.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.
> 
> I've pointed out the first thing that I noticed, thanks.
> 

I'll correct it and send the series again shortly. Thanks for catching
this.

Regards,
Naman