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

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Message-ID:
 <SN6PR02MB415711F672364610BBE6861DD48B2@SN6PR02MB4157.namprd02.prod.outlook.com>
Date: Mon, 26 Aug 2024 05:40:37 +0000
From: Michael Kelley <mhklinux@...look.com>
To: Naman Jain <namjain@...ux.microsoft.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

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