linux-kernel - Re: [PATCH] 9p: disconnect channel when PCI device is removed

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Message-ID: <CA+1xoqfQ0Cj5pibxN8ZTXbksezH4NqOERaiYav=D7BA+v86m3A@mail.gmail.com>
Date:	Sat, 28 Apr 2012 10:55:26 +0200
From:	Sasha Levin <levinsasha928@...il.com>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	davem@...emloft.net, ericvh@...il.com, jvrao@...ux.vnet.ibm.com,
	rusty@...tcorp.com.au, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, davej@...hat.com
Subject: Re: [PATCH] 9p: disconnect channel when PCI device is removed

On Mon, Apr 16, 2012 at 12:59 PM, Aneesh Kumar K.V
<aneesh.kumar@...ux.vnet.ibm.com> wrote:
> Sasha Levin <levinsasha928@...il.com> writes:
>
>> On Sun, Apr 15, 2012 at 2:27 PM, Aneesh Kumar K.V
>> <aneesh.kumar@...ux.vnet.ibm.com> wrote:
>>> Sasha Levin <levinsasha928@...il.com> writes:
>>>
>>>> When a virtio_9p pci device is being removed, we should close down any
>>>> active channels and free up resources, we're not supposed to BUG() if there's
>>>> still an open channel since it's a valid case when removing the PCI device.
>>>>
>>>> Otherwise, removing the PCI device with an open channel would cause the
>>>> following BUG():
>>>>
>>> ...
>>>
>>>> diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
>>>> index 3d43206..5af18d1 100644
>>>> --- a/net/9p/trans_virtio.c
>>>> +++ b/net/9p/trans_virtio.c
>>>> @@ -615,7 +615,8 @@ static void p9_virtio_remove(struct virtio_device *vdev)
>>>>  {
>>>>       struct virtio_chan *chan = vdev->priv;
>>>>
>>>> -     BUG_ON(chan->inuse);
>>>> +     if (chan->inuse)
>>>> +             p9_virtio_close(chan->client);
>>>>       vdev->config->del_vqs(vdev);
>>>>
>>>>       mutex_lock(&virtio_9p_lock);
>>>
>>> But an umount should have resulted in p9_virtio_close ? How are you
>>> removing the device ? Are you removing the device with file system
>>> mounted  ?. In that case may be we should return EBUSY ?
>>
>> I signal the underlying PCI device to remove (echo 1 >
>> /sys/devices/pci0000\:00/[...]/remove), we can't really prevent that
>> thing so we must clean up ourselves.
>
> What does that mean for the mounted file system ? What would happen to
> the pending fs operations in that case ?

I'm guessing that all of them should be canceled. virtio-pci simulates
a PCI device, if the PCI device is unplugged there's not much to do
about the filesystem or pending requests.
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