linux-kernel - Re: [PATCH v1 2/2] hamradio: defer 6pack kfree after unregister

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Message-ID: <20211110180612.2f2eb760@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Wed, 10 Nov 2021 18:06:12 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Lin Ma <linma@....edu.cn>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, jirislaby@...nel.org,
        gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/2] hamradio: defer 6pack kfree after
 unregister_netdev

On Wed, 10 Nov 2021 18:05:25 -0800 Jakub Kicinski wrote:
> > diff --git a/drivers/net/hamradio/6pack.c b/drivers/net/hamradio/6pack.c
> > index 49f10053a794..bfdf89e54752 100644
> > --- a/drivers/net/hamradio/6pack.c
> > +++ b/drivers/net/hamradio/6pack.c
> > @@ -672,11 +672,13 @@ static void sixpack_close(struct tty_struct *tty)
> >  	del_timer_sync(&sp->tx_t);
> >  	del_timer_sync(&sp->resync_t);
> >  
> > -	/* Free all 6pack frame buffers. */
> > +	unregister_netdev(sp->dev);
> > +
> > +	/* Free all 6pack frame buffers after unreg. */
> >  	kfree(sp->rbuff);
> >  	kfree(sp->xbuff);
> >  
> > -	unregister_netdev(sp->dev);
> > +	free_netdev(sp->dev);  
> 
> You should mention in the commit message why you think it's safe to add
> free_netdev() which wasn't here before...
> 
> This driver seems to be setting:
> 
> 	dev->needs_free_netdev	= true;
> 
> so unregister_netdev() will free the netdev automatically.
> 
> That said I don't see a reason why this driver needs the automatic
> cleanup.
> 
> You can either remove that setting and then you can call free_netdev()
> like you do, or you need to move the cleanup to dev->priv_destructor.

Looks like this go applied already, please send a follow up fix.