linux-kernel - Re: [PATCH] vmw_pvrdma: Release netdev when vmxnet3 module is removed

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Message-ID: <20180629113355.GB16153@hmswarspite.think-freely.org>
Date:   Fri, 29 Jun 2018 07:33:55 -0400
From:   Neil Horman <nhorman@...driver.com>
To:     Adit Ranadive <aditr@...are.com>
Cc:     Jason Gunthorpe <jgg@...pe.ca>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        pv-drivers <pv-drivers@...are.com>,
        Doug Ledford <dledford@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] vmw_pvrdma: Release netdev when vmxnet3 module is removed

On Thu, Jun 28, 2018 at 09:15:46PM +0000, Adit Ranadive wrote:
> On 6/28/18, 1:37 PM, "Jason Gunthorpe" <jgg@...pe.ca> wrote:
> > On Thu, Jun 28, 2018 at 03:45:26PM -0400, Neil Horman wrote:
> > > On Thu, Jun 28, 2018 at 12:59:46PM -0600, Jason Gunthorpe wrote:
> > > > On Thu, Jun 28, 2018 at 09:59:38AM -0400, Neil Horman wrote:
> > > > > On repeated module load/unload cycles, its possible for the pvrmda
> > > > > driver to encounter this crash:
> <snip>
> > > > > @@ -962,6 +982,7 @@ static int pvrdma_pci_probe(struct pci_dev *pdev,
> > > > >  	}
> > > > >  
> > > > >  	dev->netdev = pci_get_drvdata(pdev_net);
> > > > > +	dev_hold(dev->netdev);
> 
> That doesn't seem right. If the vmxnet3 driver isn't loaded at all or failed
> to create a netdev, you would be requesting a hold on a NULL netdev. What if
> you moved this to after the if(!dev->netdev) check?
> 
You're correct, I was thinking that there was a null check in dev_hold, but
there isn't, it needs to be moved after the the !dev->netdev, and released in
the error path.

> > > > >  	pci_dev_put(pdev_net);
> > > > >  	if (!dev->netdev) {
> > > > >  		dev_err(&pdev->dev, "failed to get vmxnet3 device\n");
> > > > 
> > > > I see a lot of new dev_hold's here, where are the matching
> > > > dev_puts()?
> > > > 
> > I'm not sure I'd call 2 alot, but sure, there is a new dev_hold in the
> > pvrdma_pci_probe routine, to hold a reference to the netdev that is looked up
> > there.  It is balanced by the NETDEV_UNREGISTER case in
> > pvrdma_netdevice_event_handle.  The UNREGISTER clause is also balancing the
> > NETDEV_REGISTER case of the hanlder that looks up the matching netdev should a
> > new device be registered.  Note that we will only hold a single device at a
> > time, because a given pvrdma device only recongnizes a single vmxnet3 device
> > (the one on function 0 of its own bus/device tuple).
> > 
> > I don't see how the dev_hold in pvrdma_pci_probe is undone during
> > error unwind (eg goto err_free_cq_ring)
> > 
> > And I don't see how it is put when pvrdma_pci_remove() is called.
> 
> That's right. These seem missing as well. 
> 
yup