linux-kernel - [Question] Indefinitely block in the host when remove the PF driver

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Message-ID: <c9466e2c-385d-8298-d03c-80dcfc359f52@hisilicon.com>
Date:   Fri, 30 Apr 2021 15:57:47 +0800
From:   Yicong Yang <yangyicong@...ilicon.com>
To:     Alex Williamson <alex.williamson@...hat.com>, <cohuck@...hat.com>,
        <kvm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
CC:     "Zengtao (B)" <prime.zeng@...ilicon.com>,
        Linuxarm <linuxarm@...wei.com>,
        Yicong Yang <yangyicong@...ilicon.com>
Subject: [Question] Indefinitely block in the host when remove the PF driver

When I try to remove the PF driver in the host, the process will be blocked
if the related VF of the device is added in the Qemu as an iEP.

here's what I got in the host:

[root@...alhost 0000:75:00.0]# rmmod hisi_zip
[99760.571352] vfio-pci 0000:75:00.1: Relaying device request to user (#0)
[99862.992099] vfio-pci 0000:75:00.1: Relaying device request to user (#10)
[...]

and in the Qemu:

estuary:/$ lspci -tv
-[0000:00]-+-00.0  Device 1b36:0008
           +-01.0  Device 1af4:1000
           +-02.0  Device 1af4:1009
           \-03.0  Device 19e5:a251 <----- the related VF device
estuary:/$ qemu-system-aarch64: warning: vfio 0000:75:00.1: Bus 'pcie.0' does not support hotplugging
qemu-system-aarch64: warning: vfio 0000:75:00.1: Bus 'pcie.0' does not support hotplugging
qemu-system-aarch64: warning: vfio 0000:75:00.1: Bus 'pcie.0' does not support hotplugging
qemu-system-aarch64: warning: vfio 0000:75:00.1: Bus 'pcie.0' does not support hotplugging
[...]

The rmmod process will be blocked until I kill the Qemu process. That's the only way if I
want to end the rmmod.

So my question is: is such block reasonable? If the VF devcie is occupied or doesn't
support hotplug in the Qemu, shouldn't we fail the rmmod and return something like -EBUSY
rather than make the host blocked indefinitely?

Add the VF under a pcie root port will avoid this. Is it encouraged to always
add the VF under a pcie root port rather than directly add it as an iEP?

Thanks,
Yicong