netdev - Re: [PATCH net-next v8 1/8] bnxt_en: Add auxiliary driver support

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Date:   Tue, 24 Jan 2023 08:38:25 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Ajit Khaparde <ajit.khaparde@...adcom.com>
Cc:     Jakub Kicinski <kuba@...nel.org>, andrew.gospodarek@...adcom.com,
        davem@...emloft.net, edumazet@...gle.com, jgg@...pe.ca,
        leon@...nel.org, linux-kernel@...r.kernel.org,
        linux-rdma@...r.kernel.org, michael.chan@...adcom.com,
        netdev@...r.kernel.org, pabeni@...hat.com,
        selvin.xavier@...adcom.com, Leon Romanovsky <leonro@...dia.com>
Subject: Re: [PATCH net-next v8 1/8] bnxt_en: Add auxiliary driver support

On Mon, Jan 23, 2023 at 11:07:07PM -0800, Ajit Khaparde wrote:
> On Mon, Jan 23, 2023 at 10:42 PM Greg Kroah-Hartman
> <gregkh@...uxfoundation.org> wrote:
> >
> > On Mon, Jan 23, 2023 at 10:33:05PM -0800, Jakub Kicinski wrote:
> > > On Thu, 19 Jan 2023 22:05:28 -0800 Ajit Khaparde wrote:
> > > > @@ -13212,6 +13214,7 @@ static void bnxt_remove_one(struct pci_dev *pdev)
> > > >     kfree(bp->rss_indir_tbl);
> > > >     bp->rss_indir_tbl = NULL;
> > > >     bnxt_free_port_stats(bp);
> > > > +   bnxt_aux_priv_free(bp);
> > > >     free_netdev(dev);
> > >
> > > You're still freeing the memory in which struct device sits regardless
> > > of its reference count.
> > >
> > > Greg, is it legal to call:
> > >
> > >       auxiliary_device_delete(adev);  // AKA device_del(&auxdev->dev);
> > >       auxiliary_device_uninit(adev);  // AKA put_device(&auxdev->dev);
> > >       free(adev);                     // frees struct device
> >
> > Ick, the aux device release callback should be doing the freeing of the
> > memory, you shouldn't ever have to free it "manually" like this.  To do
> > so would be a problem (i.e. the release callback would then free it
> > again, right?)
> Yikes!
> Thanks for the refresher.
> 
> >
> > > ? I tried to explain this three times, maybe there's some wait during
> > > device_del() I'm not seeing which makes this safe :S
> Apologies.
> I thought since the driver was allocating the memory, it had to free it.

Yes, you do, in the release function that will be called when the device
reference count is dropped to 0.

thanks,

greg k-h