linux-kernel - Re: [PATCH 2/2] Drivers: hv: vmbus: Fix rescind handling in uio_hv

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Message-ID: <b179947f-a37f-41ff-8893-84e9eea42462@linux.microsoft.com>
Date: Mon, 26 Aug 2024 11:14:04 +0530
From: Naman Jain <namjain@...ux.microsoft.com>
To: Michael Kelley <mhklinux@...look.com>,
 "K . Y . Srinivasan" <kys@...rosoft.com>,
 Haiyang Zhang <haiyangz@...rosoft.com>, Wei Liu <wei.liu@...nel.org>,
 Dexuan Cui <decui@...rosoft.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Stephen Hemminger <stephen@...workplumber.org>
Cc: "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 Saurabh Sengar <ssengar@...ux.microsoft.com>
Subject: Re: [PATCH 2/2] Drivers: hv: vmbus: Fix rescind handling in
 uio_hv_generic



On 8/26/2024 11:10 AM, Michael Kelley wrote:
> From: Naman Jain <namjain@...ux.microsoft.com> Sent: Sunday, August 25, 2024 10:32 PM
>>
>> On 8/25/2024 8:27 AM, Michael Kelley wrote:
>>> From: Naman Jain <namjain@...ux.microsoft.com> Sent: Thursday, August 22, 2024 4:09 AM
>>>>
>>>> Rescind offer handling relies on rescind callbacks for some of the
>>>> resources cleanup, if they are registered. It does not unregister
>>>> vmbus device for the primary channel closure, when callback is
>>>> registered.
>>>> Add logic to unregister vmbus for the primary channel in rescind callback
>>>> to ensure channel removal and relid release, and to ensure rescind flag
>>>> is false when driver probe happens again.
>>>>
>>>> Fixes: ca3cda6fcf1e ("uio_hv_generic: add rescind support")
>>>> Signed-off-by: Naman Jain <namjain@...ux.microsoft.com>
>>>> ---
>>>>    drivers/hv/vmbus_drv.c       | 1 +
>>>>    drivers/uio/uio_hv_generic.c | 7 +++++++
>>>>    2 files changed, 8 insertions(+)
>>>>
>>>> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
>>>> index c857dc3975be..4bae382a3eb4 100644
>>>> --- a/drivers/hv/vmbus_drv.c
>>>> +++ b/drivers/hv/vmbus_drv.c
>>>> @@ -1952,6 +1952,7 @@ void vmbus_device_unregister(struct hv_device *device_obj)
>>>>    	 */
>>>>    	device_unregister(&device_obj->device);
>>>>    }
>>>> +EXPORT_SYMBOL_GPL(vmbus_device_unregister);
>>>>
>>>>    #ifdef CONFIG_ACPI
>>>>    /*
>>>> diff --git a/drivers/uio/uio_hv_generic.c b/drivers/uio/uio_hv_generic.c
>>>> index c99890c16d29..ea26c0b460d6 100644
>>>> --- a/drivers/uio/uio_hv_generic.c
>>>> +++ b/drivers/uio/uio_hv_generic.c
>>>> @@ -121,6 +121,13 @@ static void hv_uio_rescind(struct vmbus_channel *channel)
>>>>
>>>>    	/* Wake up reader */
>>>>    	uio_event_notify(&pdata->info);
>>>> +
>>>> +	/*
>>>> +	 * With rescind callback registered, rescind path will not unregister the device
>>>> +	 * when the primary channel is rescinded. Without it, next onoffer msg does not come.
>>>> +	 */
>>>> +	if (!channel->primary_channel)
>>>> +		vmbus_device_unregister(channel->device_obj);
>>>
>>> When the rescind callback is *not* set, vmbus_onoffer_rescind() makes the
>>> call to vmbus_device_unregister(). But it does so bracketed with get_device()/
>>> put_device(). Your code here does not do the bracketing. Is there a reason for
>>> the difference? Frankly, I'm not sure why vmbus_onoffer_rescind() does the
>>> bracketing, and I can't definitively say if it is really needed. So I guess I'm
>>> just asking if you know. :-)
>>>
>>> Michael
>>
>> IMHO, we have already NULL checked channel->device_obj and other couple
>> of things to make sure we are safe to clean this up. At other places as
>> well, I don't see the use of put and get device. So I think its not
>> required. I am open to suggestions.
>>
>> Regards,
>> Naman
> 
> OK. I'm good with what you've said, and don't have any further suggestions.
> Go with what your patch already has. :-)
> 
> Michael

Thank you Michael. I'll wait for some time before posting v2, if there 
are any more review comments.

Regards,
Naman