linux-kernel - RE: [Patch v2 1/2] PCI: hv: Fix a race condition when removing the device

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Date:   Fri, 23 Apr 2021 18:32:24 +0000
From:   Long Li <longli@...rosoft.com>
To:     Dexuan Cui <decui@...rosoft.com>,
        "longli@...uxonhyperv.com" <longli@...uxonhyperv.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [Patch v2 1/2] PCI: hv: Fix a race condition when removing the
 device

> Subject: RE: [Patch v2 1/2] PCI: hv: Fix a race condition when removing the
> device
> 
> > From: longli@...uxonhyperv.com <longli@...uxonhyperv.com>
> > Sent: Wednesday, April 21, 2021 10:46 PM ...
> > diff --git a/drivers/pci/controller/pci-hyperv.c
> > b/drivers/pci/controller/pci-hyperv.c
> > index 27a17a1e4a7c..fc948a2ed703 100644
> > --- a/drivers/pci/controller/pci-hyperv.c
> > +++ b/drivers/pci/controller/pci-hyperv.c
> > @@ -444,7 +444,6 @@ enum hv_pcibus_state {
> >  	hv_pcibus_probed,
> >  	hv_pcibus_installed,
> >  	hv_pcibus_removing,
> > -	hv_pcibus_removed,
> >  	hv_pcibus_maximum
> >  };
> >
> > @@ -3305,13 +3304,22 @@ static int hv_pci_remove(struct hv_device
> > *hdev)
> >
> >  	hbus = hv_get_drvdata(hdev);
> >  	if (hbus->state == hv_pcibus_installed) {
> > +		tasklet_disable(&hdev->channel->callback_event);
> > +		hbus->state = hv_pcibus_removing;
> > +		tasklet_enable(&hdev->channel->callback_event);
> > +		destroy_workqueue(hbus->wq);
> 
> If we test "rmmod pci-hyperv", I suspect the warning will be printed:
> hv_pci_remove() -> hv_pci_bus_exit() -> hv_pci_start_relations_work():

In most case, it will not print anything. 

It will print something if there is a PCI_BUS_RELATION work pending at the time of remove. The same goes to PCI_EJECT. In those cases, the message is valuable to troubleshooting.

> 
>         if (hbus->state == hv_pcibus_removing) {
>                 dev_info(&hbus->hdev->device,
>                          "PCI VMBus BUS_RELATIONS: ignored\n");
>                 return -ENOENT;
>         }
> 
> Ideally we'd like to avoid the warning in the driver unloading case.
> 
> BTW, can you please add "hbus->wq = NULL;" after the line
> "destroy_workqueue(hbus->wq);"? In case some other function could still
> try to use hbus->wq by accident in the future, the error would be easier to
> be understood.

I will send v3 to add =NULL.