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

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Message-ID:
 <SN6PR02MB4157FB898345A1A8B88D1F4DD48A2@SN6PR02MB4157.namprd02.prod.outlook.com>
Date: Sun, 25 Aug 2024 02:57:08 +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: 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 +	 * when the primary channel is rescinded.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

>  }
> 
>  /* ysfs API to allow mmap of the ring buffers
> --
> 2.34.1
>