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

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Date:   Tue, 24 Jan 2023 07:42:51 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Ajit Khaparde <ajit.khaparde@...adcom.com>,
        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 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?)

> ? I tried to explain this three times, maybe there's some wait during
> device_del() I'm not seeing which makes this safe :S

Nope, no intentional wait normally.  You can add one by enabling a
debugging option to find all of the places where people are doing bad
things like this by delaying the freeing of the device memory until a
few seconds later, but that's generally not something you should run in
a production kernel as it finds all sorts of nasty bugs...

thanks,

greg k-h